{"gene":"TG_259530","gene_symbol":"","run_date":"2026-09-08T12:58:25","timeline":{"discoveries":[{"year":1997,"finding":"The T. gondii GPI glycolipid antigen bears a unique Glcα1-4GalNAc side branch on the conserved mannosyl core (structure: (ethanolamine-PO4)-Man-Man-(Glcα1-4GalNAcβ1-4)Man-GlcN-inositol-PO4-lipid), and only GPIs bearing this Glc-GalNAc side branch are immunogenic in humans; GPIs with GalNAc alone (without the terminal glucose) are not immunogenic.","method":"Exoglycosidase treatments, high pH anion-exchange chromatography, gel filtration, lectin affinity chromatography, 2D 1H-NMR, FAB-MS, methylation linkage analysis, and monoclonal antibody characterization","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal structural chemistry methods (NMR, FAB-MS, methylation analysis) plus immunological validation, single rigorous study with comprehensive characterization","pmids":["9102470"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2001,"finding":"The GPI anchor of SAG1 (P30) exists in two glycoforms: one with GalNAcβ1,4 on the first mannose, and one with an additional terminal Glcα1,4 linked to GalNAc. Core GalNAc modification of the anchor takes place prior to transfer of the GPI to the protein, as inferred by comparison with free GPI precursor structures.","method":"Isolation of GPI anchor peptides from [3H]glucosamine-labeled purified P30, gel filtration, HPEIC, exoglycosidase treatment, MALDI-TOF-MS, FAB-MS, methylation linkage analysis, aminopropyl-HPLC","journal":"Molecular and biochemical parasitology","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal structural methods (MS, exoglycosidase, methylation analysis) on purified anchor; detailed structural characterization","pmids":["11522346"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2003,"finding":"T. gondii encodes a functional UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase (ppGalNAc-T1), a type II membrane protein with GT1, Gal/GalNAc-T, and ricin lectin-like domains, that catalyzes transfer of GalNAc to Ser/Thr residues in polypeptides — the initial step of mucin-type O-glycosylation. When expressed in Drosophila S2 cells, purified recombinant protein exhibits transferase activity in vitro.","method":"cDNA library screening with degenerate PCR, stable expression in Drosophila S2 cells, in vitro transferase activity assay, Northern blot, genomic/cDNA sequence comparison","journal":"Molecular and biochemical parasitology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic activity demonstrated with recombinant protein, domain analysis by mutagenesis-inference, single lab but multiple methods","pmids":["14511808"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2004,"finding":"T. gondii encodes a family of five ppGalNAc-T isoforms (T1–T5). Three (T1, T2, T3) were fully cloned from a cDNA library, and two (T4, T5) were identified from genome sequence. All are type II membrane proteins with conserved GT1, Gal/GalNAc-T, and ricin lectin-like domains, establishing that mucin-type O-glycosylation in T. gondii is carried out by a multi-member enzyme family.","method":"cDNA library screening, genome sequence analysis, sequence alignment and domain characterization, exon structure determination","journal":"International journal for parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — gene family identification by cloning and bioinformatics; no in vitro activity demonstrated for all isoforms in this study","pmids":["15003492"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2004,"finding":"T. gondii ppGalNAc-T3 is a functional 'follow-up' (glycopeptide) O-glycosyltransferase: when expressed in Drosophila S2 cells, it transfers GalNAc to glycopeptide acceptors but NOT to 'naked' (unglycosylated) peptide acceptors, distinguishing it functionally from initiating transferases. Its mRNA is expressed equivalently in tachyzoites and bradyzoites.","method":"cDNA cloning, stable expression in Drosophila S2 cells, in vitro glycosyltransferase activity assay with peptide vs. glycopeptide acceptors, RT-PCR for stage expression","journal":"Archives of biochemistry and biophysics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic activity with substrate specificity comparison (glycopeptide vs. peptide), recombinant protein assay, single lab","pmids":["15158673"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2006,"finding":"In T. gondii grown in human cells, the GalNAc-containing GPI (without terminal Glc) is predominantly used to anchor surface proteins, while the Glcα1,4GalNAc-containing GPI is found exclusively as free glycolipid (GIPL) on the parasite cell surface, enriched in lipid microdomains associated with proteins involved in motility and host cell invasion.","method":"Metabolic labeling, phase partitioning, serology with human sera, lipid microdomain fractionation, proteomic association","journal":"The international journal of biochemistry & cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical fractionation with serological and structural validation; single lab","pmids":["16822699"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2006,"finding":"In the T. gondii GPI biosynthetic pathway, early GPI intermediates (GlcN-PI and GlcNAc-PI) are predominantly localized in the cytoplasmic leaflet of the ER membrane. More highly mannosylated and Glc-GalNAc-modified GPI intermediates are also preferentially in the cytoplasmic leaflet of the ER.","method":"Hypotonic permeabilization of T. gondii tachyzoites, metabolic labeling with UDP-[3H]GlcNAc, GDP-[3H]mannose, or UDP-[3H]glucose, PI-PLC treatment to assess membrane topology, electron microscopy, protease protection assays","journal":"Eukaryotic cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct topological probing with PI-PLC in permeabilized parasites, multiple labeling substrates, single lab","pmids":["16896225"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2007,"finding":"In the T. gondii GPI biosynthetic pathway, inositol acylation (acyl-CoA-dependent) occurs before mannosylation and is inhibited by PMSF. Inositol deacylation of the fully mannosylated GPI intermediate (also inhibited by PMSF and DFP) must precede addition of the GalNAc side chain to the first mannose. The sn-2 position of the diacylglycerol lipid moiety in both free GPIs and GPI-anchored proteins contains almost exclusively a C18:1 acyl chain.","method":"In vitro GPI biosynthesis assays with radiolabeled substrates, use of serine protease inhibitors (PMSF, DFP) as pathway probes, structural characterization of GPI intermediates and products","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — biochemical pathway dissection with pharmacological probes and radiolabeled intermediates; establishes ordering of GalNAc addition in biosynthetic pathway","pmids":["17804418"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2017,"finding":"ppGalNAc-T2 and ppGalNAc-T3 are the two isoforms responsible for O-GalNAc glycosylation of the cyst wall mucin-like glycoprotein CST1 in T. gondii, acting in a hierarchical manner: T2 performs the initial glycosylation of the mucin-like domain's threonine-rich tandem repeats, while T3 fills in subsequent neighboring acceptor sites. This glycosylation is required for CST1 to confer structural rigidity on brain cysts. Deletion of T2 or T3 produces glycosylation defects on multiple cyst wall glycoproteins.","method":"Individual CRISPR/Cas9 deletion of all five ppGalNAc-T isoforms, glycan analysis of cyst walls, cyst wall rigidity assays, mutagenesis-based assignment of hierarchical glycosylation, immunofluorescence","journal":"mBio","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean individual knockouts of all five isoforms with multiple orthogonal readouts (glycomics, structural rigidity, immunofluorescence); hierarchical mechanism established in intact organism","pmids":["28074022"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2018,"finding":"By coupling CRISPR/Cas9 gene editing with MS-based glycomics, T. gondii ppGalNAc-T activity was shown to be required for Tn-antigen (GalNAc-Ser/Thr) and a novel HexNAc-GalNAc mucin-type O-glycan. The study also identified and characterized an O-glycosylation pathway yielding novel nuclear O-Fuc-type and cell-surface Glc-Fuc-type O-glycans from separate glycosyltransferases, with the latter being important for in vitro growth.","method":"Double-CRISPR/Cas9 gene replacement of 17 glycogenes, MS-based glycomics, fibroblast infection growth assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic genetic disruption combined with MS glycomics; multiple glycogenes and glycan products mapped; in vitro growth phenotypes; replicated across multiple targets","pmids":["30463938"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2018,"finding":"SRS13, a novel mucin-domain-containing SRS protein, is O-GalNAc glycosylated by ppGalNAc-T2 and T3, localizes to the cyst wall in bradyzoites, but is dispensable for normal cyst wall formation.","method":"Glycoepitope-specific antibody identification, immunofluorescence localization, genetic characterization, stage-specific expression analysis","journal":"Parasitology research","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — localization and O-GalNAc glycosylation by T2/T3 established by antibody and expression data; dispensability by knockout; single lab","pmids":["29911257"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2024,"finding":"X-ray crystal structures of T. gondii ppGalNAc-T3 (TxgGalNAc-T3) reveal multiple features strictly conserved among apicomplexan homologues including a unique second metal ion that is coupled to substrate binding and enzymatic activity in vitro. This second metal is required for cyst wall O-glycosylation in T. gondii. The enzyme's structure diverges from host homologues, suggesting potential as a therapeutic target.","method":"X-ray crystallography, in vitro enzymatic activity assays with mutagenesis of metal-binding residues, cyst wall O-glycosylation assessment in T. gondii","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus mutagenesis of active site residues plus in vitro activity and in vivo cyst wall glycosylation validation; multiple orthogonal methods in single rigorous study","pmids":["38710711"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2024,"finding":"Two glycosyltransferases responsible for building the GPI Glcα1,4GalNAcβ1 sidechain were identified: PIGJ adds the first GalNAc to the sidechain. Deletion of PIGJ abolishes the sidechain, increases parasite virulence, enhances scavenger receptor CD36 binding, and elevates galectin-3 binding to GIPLs, while antibody recognition of GPI-anchored SAGs and complement binding remain intact. Deletion of the second glycosyltransferase (adds Glc to GalNAc) leaves GalNAc-only sidechain with negligible effect on disease outcome.","method":"CRISPR/Cas9 deletion of PIGJ and second glycosyltransferase, serology, mass spectrometry for GPI structure confirmation, mouse virulence assays (WT and galectin-3 KO mice), CD36 binding assays, complement binding assays, brain cyst quantification","journal":"mBio","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic knockouts with structural MS confirmation, multiple in vitro and in vivo functional readouts, galectin-3 KO epistasis experiment, single lab but multiple orthogonal methods","pmids":["39302131"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"In Toxoplasma gondii, GalNAc modifications occur in two distinct contexts: (1) GPI anchor biosynthesis, where PIGJ adds a GalNAcβ1-4 residue to the first mannose of the GPI core after inositol deacylation, and a second glycosyltransferase subsequently adds a terminal Glcα1-4 to generate the immunogenic Glc-GalNAc sidechain that modulates host-parasite interactions including CD36 and galectin-3 binding; and (2) mucin-type O-glycosylation of cyst wall proteins, initiated by ppGalNAc-T2 (which performs initial GalNAc transfer to Ser/Thr on unmodified peptide) and extended by ppGalNAc-T3 (a follow-up glycopeptide transferase with a unique second catalytic metal ion visible in crystal structures), whose hierarchical glycosylation of CST1 and other cyst wall glycoproteins is required for structural rigidity of T. gondii brain cysts."},"narrative":{"mechanistic_narrative":"GalNAc modifications in Toxoplasma gondii occur in two mechanistically distinct glycosylation programs that shape host-parasite interactions and cyst biology [PMID:9102470, PMID:28074022]. In GPI anchor biosynthesis, the parasite generates a characteristic Glcα1-4GalNAcβ1-4 side branch on the mannosyl core, and only GPIs bearing the terminal glucose on GalNAc are immunogenic in humans [PMID:9102470]; this core GalNAc modification is added to the free GPI precursor before transfer to protein [PMID:11522346], following an ordered pathway in which inositol deacylation of the fully mannosylated intermediate must precede GalNAc side-chain addition [PMID:17804418]. The two enzymes that build this side chain are PIGJ, which transfers the first GalNAc, and a second glycosyltransferase, which caps it with glucose; loss of PIGJ abolishes the side chain, increases virulence, and enhances CD36 and galectin-3 binding of parasite GIPLs, whereas removal of only the terminal glucose leaves a GalNAc-only side chain with negligible effect on disease [PMID:39302131]. The two GPI glycoforms are partitioned functionally: the GalNAc-only anchor predominantly attaches surface proteins, while the Glc-GalNAc form persists as free glycolipid in surface lipid microdomains [PMID:16822699]. Separately, mucin-type O-glycosylation is initiated by transfer of GalNAc to Ser/Thr residues by a family of five polypeptide N-acetylgalactosaminyltransferases (ppGalNAc-T1 to T5) [PMID:14511808, PMID:15003492]. ppGalNAc-T2 performs initial glycosylation of the threonine-rich tandem repeats of the cyst wall glycoprotein CST1, and the glycopeptide-specific follow-up transferase ppGalNAc-T3 fills in neighboring acceptor sites; this hierarchical O-glycosylation is required for the structural rigidity of brain cysts [PMID:15158673, PMID:28074022]. Crystal structures of ppGalNAc-T3 reveal a unique second catalytic metal ion coupled to substrate binding that is required for cyst wall O-glycosylation and distinguishes the enzyme from host homologues [PMID:38710711].","teleology":[{"year":1997,"claim":"Defining the structure of the immunogenic T. gondii GPI established that a Glcα1-4GalNAc side branch on the mannosyl core, not GalNAc alone, is the determinant of human immunogenicity.","evidence":"Exoglycosidase treatment, NMR, FAB-MS, methylation linkage analysis, and monoclonal antibody characterization of purified GPI glycolipid","pmids":["9102470"],"confidence":"High","gaps":["The enzymes building the side chain were not yet identified","Functional consequences of the side branch for host interaction unaddressed"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2001,"claim":"Showing that the SAG1 anchor exists as GalNAc-only and Glc-GalNAc glycoforms and that core GalNAc is added before protein transfer placed the modification within the free GPI precursor pathway.","evidence":"Structural analysis of GPI anchor peptides from radiolabeled purified P30 by MS, exoglycosidase, and methylation analysis","pmids":["11522346"],"confidence":"High","gaps":["The transferases responsible were not identified","Whether the two glycoforms have distinct fates was unresolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2003,"claim":"Cloning and functional expression of ppGalNAc-T1 established that T. gondii initiates mucin-type O-glycosylation by transferring GalNAc to Ser/Thr, a program distinct from GPI GalNAc modification.","evidence":"cDNA cloning, expression in Drosophila S2 cells, and in vitro transferase activity assay","pmids":["14511808"],"confidence":"High","gaps":["Physiological substrates in vivo not identified","Only one isoform functionally characterized"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2004,"claim":"Identifying a five-member ppGalNAc-T family and demonstrating that T3 acts only on glycopeptide (not naked peptide) acceptors defined an initiating-versus-follow-up division of labor in O-glycosylation.","evidence":"cDNA and genomic cloning of five isoforms; in vitro activity of T3 on peptide versus glycopeptide acceptors expressed in S2 cells; stage-specific RT-PCR","pmids":["15003492","15158673"],"confidence":"High","gaps":["In vivo substrates and biological role of the family not defined","Enzymatic activity not demonstrated for all five isoforms"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2006,"claim":"Membrane topology and glycoform partitioning studies established where GPI intermediates are assembled and that the two GalNAc glycoforms are functionally segregated between protein anchoring and free surface glycolipid.","evidence":"PI-PLC topology assays in permeabilized parasites; metabolic labeling with phase partitioning and lipid microdomain fractionation","pmids":["16896225","16822699"],"confidence":"Medium","gaps":["Molecular basis for glycoform sorting unknown","Enzymes adding side-chain sugars not identified"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2007,"claim":"Dissecting the biosynthetic ordering showed inositol deacylation of the mannosylated intermediate must precede GalNAc side-chain addition, fixing GalNAc modification at a defined step of GPI assembly.","evidence":"In vitro GPI biosynthesis with radiolabeled substrates and serine protease inhibitors as pathway probes","pmids":["17804418"],"confidence":"High","gaps":["The GalNAc transferase for the GPI side chain was not yet identified","Regulation of the deacylation step unknown"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2017,"claim":"CRISPR deletion of all five isoforms established that ppGalNAc-T2 and T3 hierarchically O-glycosylate CST1 and are required for brain cyst structural rigidity, tying O-glycosylation to a defined biological function.","evidence":"Individual CRISPR/Cas9 knockouts of all five isoforms, cyst wall glycan analysis, rigidity assays, and immunofluorescence","pmids":["28074022"],"confidence":"High","gaps":["Full set of glycosylated cyst wall targets not enumerated","Structural basis of T3 glycopeptide specificity unresolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2018,"claim":"Systematic glycogene disruption with MS glycomics defined the ppGalNAc-T-dependent Tn and HexNAc-GalNAc O-glycans and mapped additional O-Fuc/Glc-Fuc pathways, and identified further mucin-domain substrates such as SRS13.","evidence":"Double-CRISPR/Cas9 gene replacement of multiple glycogenes with MS glycomics and fibroblast growth assays; glycoepitope antibody and localization for SRS13","pmids":["30463938","29911257"],"confidence":"High","gaps":["Individual acceptor-site contributions of each isoform not fully resolved","SRS13 dispensable, so its functional role remains unclear"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2024,"claim":"Structural determination of ppGalNAc-T3 and genetic identification of the GPI side-chain transferases resolved the catalytic machinery and host-interaction consequences of both GalNAc programs.","evidence":"X-ray crystallography with active-site mutagenesis and in vivo cyst glycosylation for T3; CRISPR deletion of PIGJ and the terminal glucose transferase with MS, virulence, CD36, galectin-3 and complement binding assays","pmids":["38710711","39302131"],"confidence":"High","gaps":["The identity of the terminal glucose transferase enzyme was defined only by phenotype in this corpus","Mechanism by which the side chain restrains virulence via CD36/galectin-3 not fully resolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"How the two GalNAc glycoforms of the GPI anchor are sorted between protein anchoring and free surface glycolipid, and the full contribution of individual ppGalNAc-T isoforms to specific in vivo substrates, remain open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Molecular sorting machinery for GPI glycoforms unknown","Isoform-specific acceptor-site rules in vivo incompletely defined"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":["CST1 (CYST WALL MUCIN-LIKE GLYCOPROTEIN, O-GALNAC SUBSTRATE OF PPGALNAC-T2/T3)","SRS13 (MUCIN-DOMAIN SRS PROTEIN, O-GALNAC SUBSTRATE OF PPGALNAC-T2/T3)","SAG1/P30 (GPI-ANCHORED SURFACE PROTEIN BEARING CORE GALNAC GLYCOFORMS)","CD36 (HOST SCAVENGER RECEPTOR BOUND BY GIPLS, MODULATED BY PIGJ SIDE CHAIN)","GALECTIN-3 (HOST LECTIN BINDING GIPLS, MODULATED BY PIGJ SIDE CHAIN)"],"other_free_text":["GalNAc modification operates in two distinct T. gondii pathways: GPI anchor Glcα1-4GalNAcβ1-4 side-chain biosynthesis (PIGJ plus a terminal glucose transferase) and mucin-type O-glycosylation (ppGalNAc-T family).","Only GPIs bearing the terminal Glc on GalNAc are immunogenic; PIGJ deletion abolishing the side chain increases virulence and enhances CD36 and galectin-3 binding.","Core GalNAc is added to the free GPI precursor after inositol deacylation and before transfer to protein.","ppGalNAc-T2 initiates and ppGalNAc-T3 follows up hierarchical O-glycosylation of cyst wall glycoproteins, required for brain cyst structural rigidity.","ppGalNAc-T3 possesses a unique second catalytic metal ion coupled to substrate binding and required for cyst wall O-glycosylation, diverging from host homologues."]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"9102470","id":"PMC_9102470","title":"Molecular structure of the \"low molecular weight antigen\" of Toxoplasma gondii: a glucose alpha 1-4 N-acetylgalactosamine makes free glycosyl-phosphatidylinositols highly immunogenic.","date":"1997","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/9102470","citation_count":70,"is_preprint":false},{"pmid":"24096907","id":"PMC_24096907","title":"Strategies to discover the structural components of cyst and oocyst walls.","date":"2013","source":"Eukaryotic cell","url":"https://pubmed.ncbi.nlm.nih.gov/24096907","citation_count":64,"is_preprint":false},{"pmid":"28074022","id":"PMC_28074022","title":"Making Home Sweet and Sturdy: Toxoplasma gondii ppGalNAc-Ts Glycosylate in Hierarchical Order and Confer Cyst Wall Rigidity.","date":"2017","source":"mBio","url":"https://pubmed.ncbi.nlm.nih.gov/28074022","citation_count":52,"is_preprint":false},{"pmid":"30463938","id":"PMC_30463938","title":"CRISPR/Cas9 and glycomics tools for Toxoplasma glycobiology.","date":"2018","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/30463938","citation_count":48,"is_preprint":false},{"pmid":"14500524","id":"PMC_14500524","title":"Expression of Cpgp40/15 in Toxoplasma gondii: a surrogate system for the study of Cryptosporidium glycoprotein antigens.","date":"2003","source":"Infection and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/14500524","citation_count":41,"is_preprint":false},{"pmid":"14511808","id":"PMC_14511808","title":"cDNA cloning and expression of UDP-N-acetyl-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase T1 from Toxoplasma gondii.","date":"2003","source":"Molecular and biochemical parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/14511808","citation_count":35,"is_preprint":false},{"pmid":"23015739","id":"PMC_23015739","title":"β-1,3-glucan, which can be targeted by drugs, forms a trabecular scaffold in the oocyst walls of Toxoplasma and Eimeria.","date":"2012","source":"mBio","url":"https://pubmed.ncbi.nlm.nih.gov/23015739","citation_count":34,"is_preprint":false},{"pmid":"15003492","id":"PMC_15003492","title":"O-glycosylation in Toxoplasma gondii: identification and analysis of a family of UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases.","date":"2004","source":"International journal for parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/15003492","citation_count":33,"is_preprint":false},{"pmid":"11522346","id":"PMC_11522346","title":"Two glycoforms are present in the GPI-membrane anchor of the surface antigen 1 (P30) of Toxoplasma gondii.","date":"2001","source":"Molecular and biochemical parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/11522346","citation_count":25,"is_preprint":false},{"pmid":"16822699","id":"PMC_16822699","title":"Toxoplasma gondii grown in human cells uses GalNAc-containing glycosylphosphatidylinositol precursors to anchor surface antigens while the immunogenic Glc-GalNAc-containing precursors remain free at the parasite cell surface.","date":"2006","source":"The international journal of biochemistry & cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/16822699","citation_count":20,"is_preprint":false},{"pmid":"15158673","id":"PMC_15158673","title":"Functional characterization of a novel Toxoplasma gondii glycosyltransferase: UDP-N-acetyl-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase-T3.","date":"2004","source":"Archives of biochemistry and biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/15158673","citation_count":18,"is_preprint":false},{"pmid":"29911257","id":"PMC_29911257","title":"Characterization of a SRS13: a new cyst wall mucin-like domain containing protein.","date":"2018","source":"Parasitology research","url":"https://pubmed.ncbi.nlm.nih.gov/29911257","citation_count":12,"is_preprint":false},{"pmid":"17804418","id":"PMC_17804418","title":"The role of inositol acylation and inositol deacylation in the Toxoplasma gondii glycosylphosphatidylinositol biosynthetic pathway.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17804418","citation_count":12,"is_preprint":false},{"pmid":"38710711","id":"PMC_38710711","title":"A Toxoplasma gondii O-glycosyltransferase that modulates bradyzoite cyst wall rigidity is distinct from host homologues.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/38710711","citation_count":8,"is_preprint":false},{"pmid":"38623843","id":"PMC_38623843","title":"Molecular regulation of NLRP3 inflammasome activation during parasitic infection.","date":"2024","source":"Bioscience reports","url":"https://pubmed.ncbi.nlm.nih.gov/38623843","citation_count":7,"is_preprint":false},{"pmid":"16896225","id":"PMC_16896225","title":"Membrane topology and transient acylation of Toxoplasma gondii glycosylphosphatidylinositols.","date":"2006","source":"Eukaryotic cell","url":"https://pubmed.ncbi.nlm.nih.gov/16896225","citation_count":6,"is_preprint":false},{"pmid":"39302131","id":"PMC_39302131","title":"The GPI sidechain of Toxoplasma gondii inhibits parasite pathogenesis.","date":"2024","source":"mBio","url":"https://pubmed.ncbi.nlm.nih.gov/39302131","citation_count":4,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12283,"output_tokens":4384,"usd":0.051305,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10652,"output_tokens":4678,"usd":0.085105,"stage2_stop_reason":"end_turn"},"total_usd":0.13641,"stage1_batch_id":"msgbatch_01TEPNZ4MCzJ7xtsNwosiDRk","stage2_batch_id":"msgbatch_01FQShM7n1sfCr4pWTDShmki","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"The T. gondii GPI glycolipid antigen bears a unique Glcα1-4GalNAc side branch on the conserved mannosyl core (structure: (ethanolamine-PO4)-Man-Man-(Glcα1-4GalNAcβ1-4)Man-GlcN-inositol-PO4-lipid), and only GPIs bearing this Glc-GalNAc side branch are immunogenic in humans; GPIs with GalNAc alone (without the terminal glucose) are not immunogenic.\",\n      \"method\": \"Exoglycosidase treatments, high pH anion-exchange chromatography, gel filtration, lectin affinity chromatography, 2D 1H-NMR, FAB-MS, methylation linkage analysis, and monoclonal antibody characterization\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal structural chemistry methods (NMR, FAB-MS, methylation analysis) plus immunological validation, single rigorous study with comprehensive characterization\",\n      \"pmids\": [\"9102470\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The GPI anchor of SAG1 (P30) exists in two glycoforms: one with GalNAcβ1,4 on the first mannose, and one with an additional terminal Glcα1,4 linked to GalNAc. Core GalNAc modification of the anchor takes place prior to transfer of the GPI to the protein, as inferred by comparison with free GPI precursor structures.\",\n      \"method\": \"Isolation of GPI anchor peptides from [3H]glucosamine-labeled purified P30, gel filtration, HPEIC, exoglycosidase treatment, MALDI-TOF-MS, FAB-MS, methylation linkage analysis, aminopropyl-HPLC\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal structural methods (MS, exoglycosidase, methylation analysis) on purified anchor; detailed structural characterization\",\n      \"pmids\": [\"11522346\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"T. gondii encodes a functional UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase (ppGalNAc-T1), a type II membrane protein with GT1, Gal/GalNAc-T, and ricin lectin-like domains, that catalyzes transfer of GalNAc to Ser/Thr residues in polypeptides — the initial step of mucin-type O-glycosylation. When expressed in Drosophila S2 cells, purified recombinant protein exhibits transferase activity in vitro.\",\n      \"method\": \"cDNA library screening with degenerate PCR, stable expression in Drosophila S2 cells, in vitro transferase activity assay, Northern blot, genomic/cDNA sequence comparison\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic activity demonstrated with recombinant protein, domain analysis by mutagenesis-inference, single lab but multiple methods\",\n      \"pmids\": [\"14511808\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"T. gondii encodes a family of five ppGalNAc-T isoforms (T1–T5). Three (T1, T2, T3) were fully cloned from a cDNA library, and two (T4, T5) were identified from genome sequence. All are type II membrane proteins with conserved GT1, Gal/GalNAc-T, and ricin lectin-like domains, establishing that mucin-type O-glycosylation in T. gondii is carried out by a multi-member enzyme family.\",\n      \"method\": \"cDNA library screening, genome sequence analysis, sequence alignment and domain characterization, exon structure determination\",\n      \"journal\": \"International journal for parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — gene family identification by cloning and bioinformatics; no in vitro activity demonstrated for all isoforms in this study\",\n      \"pmids\": [\"15003492\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"T. gondii ppGalNAc-T3 is a functional 'follow-up' (glycopeptide) O-glycosyltransferase: when expressed in Drosophila S2 cells, it transfers GalNAc to glycopeptide acceptors but NOT to 'naked' (unglycosylated) peptide acceptors, distinguishing it functionally from initiating transferases. Its mRNA is expressed equivalently in tachyzoites and bradyzoites.\",\n      \"method\": \"cDNA cloning, stable expression in Drosophila S2 cells, in vitro glycosyltransferase activity assay with peptide vs. glycopeptide acceptors, RT-PCR for stage expression\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic activity with substrate specificity comparison (glycopeptide vs. peptide), recombinant protein assay, single lab\",\n      \"pmids\": [\"15158673\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In T. gondii grown in human cells, the GalNAc-containing GPI (without terminal Glc) is predominantly used to anchor surface proteins, while the Glcα1,4GalNAc-containing GPI is found exclusively as free glycolipid (GIPL) on the parasite cell surface, enriched in lipid microdomains associated with proteins involved in motility and host cell invasion.\",\n      \"method\": \"Metabolic labeling, phase partitioning, serology with human sera, lipid microdomain fractionation, proteomic association\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical fractionation with serological and structural validation; single lab\",\n      \"pmids\": [\"16822699\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In the T. gondii GPI biosynthetic pathway, early GPI intermediates (GlcN-PI and GlcNAc-PI) are predominantly localized in the cytoplasmic leaflet of the ER membrane. More highly mannosylated and Glc-GalNAc-modified GPI intermediates are also preferentially in the cytoplasmic leaflet of the ER.\",\n      \"method\": \"Hypotonic permeabilization of T. gondii tachyzoites, metabolic labeling with UDP-[3H]GlcNAc, GDP-[3H]mannose, or UDP-[3H]glucose, PI-PLC treatment to assess membrane topology, electron microscopy, protease protection assays\",\n      \"journal\": \"Eukaryotic cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct topological probing with PI-PLC in permeabilized parasites, multiple labeling substrates, single lab\",\n      \"pmids\": [\"16896225\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In the T. gondii GPI biosynthetic pathway, inositol acylation (acyl-CoA-dependent) occurs before mannosylation and is inhibited by PMSF. Inositol deacylation of the fully mannosylated GPI intermediate (also inhibited by PMSF and DFP) must precede addition of the GalNAc side chain to the first mannose. The sn-2 position of the diacylglycerol lipid moiety in both free GPIs and GPI-anchored proteins contains almost exclusively a C18:1 acyl chain.\",\n      \"method\": \"In vitro GPI biosynthesis assays with radiolabeled substrates, use of serine protease inhibitors (PMSF, DFP) as pathway probes, structural characterization of GPI intermediates and products\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — biochemical pathway dissection with pharmacological probes and radiolabeled intermediates; establishes ordering of GalNAc addition in biosynthetic pathway\",\n      \"pmids\": [\"17804418\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ppGalNAc-T2 and ppGalNAc-T3 are the two isoforms responsible for O-GalNAc glycosylation of the cyst wall mucin-like glycoprotein CST1 in T. gondii, acting in a hierarchical manner: T2 performs the initial glycosylation of the mucin-like domain's threonine-rich tandem repeats, while T3 fills in subsequent neighboring acceptor sites. This glycosylation is required for CST1 to confer structural rigidity on brain cysts. Deletion of T2 or T3 produces glycosylation defects on multiple cyst wall glycoproteins.\",\n      \"method\": \"Individual CRISPR/Cas9 deletion of all five ppGalNAc-T isoforms, glycan analysis of cyst walls, cyst wall rigidity assays, mutagenesis-based assignment of hierarchical glycosylation, immunofluorescence\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean individual knockouts of all five isoforms with multiple orthogonal readouts (glycomics, structural rigidity, immunofluorescence); hierarchical mechanism established in intact organism\",\n      \"pmids\": [\"28074022\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"By coupling CRISPR/Cas9 gene editing with MS-based glycomics, T. gondii ppGalNAc-T activity was shown to be required for Tn-antigen (GalNAc-Ser/Thr) and a novel HexNAc-GalNAc mucin-type O-glycan. The study also identified and characterized an O-glycosylation pathway yielding novel nuclear O-Fuc-type and cell-surface Glc-Fuc-type O-glycans from separate glycosyltransferases, with the latter being important for in vitro growth.\",\n      \"method\": \"Double-CRISPR/Cas9 gene replacement of 17 glycogenes, MS-based glycomics, fibroblast infection growth assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic genetic disruption combined with MS glycomics; multiple glycogenes and glycan products mapped; in vitro growth phenotypes; replicated across multiple targets\",\n      \"pmids\": [\"30463938\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SRS13, a novel mucin-domain-containing SRS protein, is O-GalNAc glycosylated by ppGalNAc-T2 and T3, localizes to the cyst wall in bradyzoites, but is dispensable for normal cyst wall formation.\",\n      \"method\": \"Glycoepitope-specific antibody identification, immunofluorescence localization, genetic characterization, stage-specific expression analysis\",\n      \"journal\": \"Parasitology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — localization and O-GalNAc glycosylation by T2/T3 established by antibody and expression data; dispensability by knockout; single lab\",\n      \"pmids\": [\"29911257\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"X-ray crystal structures of T. gondii ppGalNAc-T3 (TxgGalNAc-T3) reveal multiple features strictly conserved among apicomplexan homologues including a unique second metal ion that is coupled to substrate binding and enzymatic activity in vitro. This second metal is required for cyst wall O-glycosylation in T. gondii. The enzyme's structure diverges from host homologues, suggesting potential as a therapeutic target.\",\n      \"method\": \"X-ray crystallography, in vitro enzymatic activity assays with mutagenesis of metal-binding residues, cyst wall O-glycosylation assessment in T. gondii\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus mutagenesis of active site residues plus in vitro activity and in vivo cyst wall glycosylation validation; multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"38710711\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Two glycosyltransferases responsible for building the GPI Glcα1,4GalNAcβ1 sidechain were identified: PIGJ adds the first GalNAc to the sidechain. Deletion of PIGJ abolishes the sidechain, increases parasite virulence, enhances scavenger receptor CD36 binding, and elevates galectin-3 binding to GIPLs, while antibody recognition of GPI-anchored SAGs and complement binding remain intact. Deletion of the second glycosyltransferase (adds Glc to GalNAc) leaves GalNAc-only sidechain with negligible effect on disease outcome.\",\n      \"method\": \"CRISPR/Cas9 deletion of PIGJ and second glycosyltransferase, serology, mass spectrometry for GPI structure confirmation, mouse virulence assays (WT and galectin-3 KO mice), CD36 binding assays, complement binding assays, brain cyst quantification\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic knockouts with structural MS confirmation, multiple in vitro and in vivo functional readouts, galectin-3 KO epistasis experiment, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"39302131\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"In Toxoplasma gondii, GalNAc modifications occur in two distinct contexts: (1) GPI anchor biosynthesis, where PIGJ adds a GalNAcβ1-4 residue to the first mannose of the GPI core after inositol deacylation, and a second glycosyltransferase subsequently adds a terminal Glcα1-4 to generate the immunogenic Glc-GalNAc sidechain that modulates host-parasite interactions including CD36 and galectin-3 binding; and (2) mucin-type O-glycosylation of cyst wall proteins, initiated by ppGalNAc-T2 (which performs initial GalNAc transfer to Ser/Thr on unmodified peptide) and extended by ppGalNAc-T3 (a follow-up glycopeptide transferase with a unique second catalytic metal ion visible in crystal structures), whose hierarchical glycosylation of CST1 and other cyst wall glycoproteins is required for structural rigidity of T. gondii brain cysts.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GalNAc modifications in Toxoplasma gondii occur in two mechanistically distinct glycosylation programs that shape host-parasite interactions and cyst biology [#0, #8]. In GPI anchor biosynthesis, the parasite generates a characteristic Glcα1-4GalNAcβ1-4 side branch on the mannosyl core, and only GPIs bearing the terminal glucose on GalNAc are immunogenic in humans [#0]; this core GalNAc modification is added to the free GPI precursor before transfer to protein [#1], following an ordered pathway in which inositol deacylation of the fully mannosylated intermediate must precede GalNAc side-chain addition [#7]. The two enzymes that build this side chain are PIGJ, which transfers the first GalNAc, and a second glycosyltransferase, which caps it with glucose; loss of PIGJ abolishes the side chain, increases virulence, and enhances CD36 and galectin-3 binding of parasite GIPLs, whereas removal of only the terminal glucose leaves a GalNAc-only side chain with negligible effect on disease [#12]. The two GPI glycoforms are partitioned functionally: the GalNAc-only anchor predominantly attaches surface proteins, while the Glc-GalNAc form persists as free glycolipid in surface lipid microdomains [#5]. Separately, mucin-type O-glycosylation is initiated by transfer of GalNAc to Ser/Thr residues by a family of five polypeptide N-acetylgalactosaminyltransferases (ppGalNAc-T1 to T5) [#2, #3]. ppGalNAc-T2 performs initial glycosylation of the threonine-rich tandem repeats of the cyst wall glycoprotein CST1, and the glycopeptide-specific follow-up transferase ppGalNAc-T3 fills in neighboring acceptor sites; this hierarchical O-glycosylation is required for the structural rigidity of brain cysts [#4, #8]. Crystal structures of ppGalNAc-T3 reveal a unique second catalytic metal ion coupled to substrate binding that is required for cyst wall O-glycosylation and distinguishes the enzyme from host homologues [#11].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Defining the structure of the immunogenic T. gondii GPI established that a Glcα1-4GalNAc side branch on the mannosyl core, not GalNAc alone, is the determinant of human immunogenicity.\",\n      \"evidence\": \"Exoglycosidase treatment, NMR, FAB-MS, methylation linkage analysis, and monoclonal antibody characterization of purified GPI glycolipid\",\n      \"pmids\": [\"9102470\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The enzymes building the side chain were not yet identified\", \"Functional consequences of the side branch for host interaction unaddressed\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Showing that the SAG1 anchor exists as GalNAc-only and Glc-GalNAc glycoforms and that core GalNAc is added before protein transfer placed the modification within the free GPI precursor pathway.\",\n      \"evidence\": \"Structural analysis of GPI anchor peptides from radiolabeled purified P30 by MS, exoglycosidase, and methylation analysis\",\n      \"pmids\": [\"11522346\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The transferases responsible were not identified\", \"Whether the two glycoforms have distinct fates was unresolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Cloning and functional expression of ppGalNAc-T1 established that T. gondii initiates mucin-type O-glycosylation by transferring GalNAc to Ser/Thr, a program distinct from GPI GalNAc modification.\",\n      \"evidence\": \"cDNA cloning, expression in Drosophila S2 cells, and in vitro transferase activity assay\",\n      \"pmids\": [\"14511808\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological substrates in vivo not identified\", \"Only one isoform functionally characterized\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identifying a five-member ppGalNAc-T family and demonstrating that T3 acts only on glycopeptide (not naked peptide) acceptors defined an initiating-versus-follow-up division of labor in O-glycosylation.\",\n      \"evidence\": \"cDNA and genomic cloning of five isoforms; in vitro activity of T3 on peptide versus glycopeptide acceptors expressed in S2 cells; stage-specific RT-PCR\",\n      \"pmids\": [\"15003492\", \"15158673\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo substrates and biological role of the family not defined\", \"Enzymatic activity not demonstrated for all five isoforms\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Membrane topology and glycoform partitioning studies established where GPI intermediates are assembled and that the two GalNAc glycoforms are functionally segregated between protein anchoring and free surface glycolipid.\",\n      \"evidence\": \"PI-PLC topology assays in permeabilized parasites; metabolic labeling with phase partitioning and lipid microdomain fractionation\",\n      \"pmids\": [\"16896225\", \"16822699\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis for glycoform sorting unknown\", \"Enzymes adding side-chain sugars not identified\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Dissecting the biosynthetic ordering showed inositol deacylation of the mannosylated intermediate must precede GalNAc side-chain addition, fixing GalNAc modification at a defined step of GPI assembly.\",\n      \"evidence\": \"In vitro GPI biosynthesis with radiolabeled substrates and serine protease inhibitors as pathway probes\",\n      \"pmids\": [\"17804418\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The GalNAc transferase for the GPI side chain was not yet identified\", \"Regulation of the deacylation step unknown\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"CRISPR deletion of all five isoforms established that ppGalNAc-T2 and T3 hierarchically O-glycosylate CST1 and are required for brain cyst structural rigidity, tying O-glycosylation to a defined biological function.\",\n      \"evidence\": \"Individual CRISPR/Cas9 knockouts of all five isoforms, cyst wall glycan analysis, rigidity assays, and immunofluorescence\",\n      \"pmids\": [\"28074022\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full set of glycosylated cyst wall targets not enumerated\", \"Structural basis of T3 glycopeptide specificity unresolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Systematic glycogene disruption with MS glycomics defined the ppGalNAc-T-dependent Tn and HexNAc-GalNAc O-glycans and mapped additional O-Fuc/Glc-Fuc pathways, and identified further mucin-domain substrates such as SRS13.\",\n      \"evidence\": \"Double-CRISPR/Cas9 gene replacement of multiple glycogenes with MS glycomics and fibroblast growth assays; glycoepitope antibody and localization for SRS13\",\n      \"pmids\": [\"30463938\", \"29911257\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Individual acceptor-site contributions of each isoform not fully resolved\", \"SRS13 dispensable, so its functional role remains unclear\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Structural determination of ppGalNAc-T3 and genetic identification of the GPI side-chain transferases resolved the catalytic machinery and host-interaction consequences of both GalNAc programs.\",\n      \"evidence\": \"X-ray crystallography with active-site mutagenesis and in vivo cyst glycosylation for T3; CRISPR deletion of PIGJ and the terminal glucose transferase with MS, virulence, CD36, galectin-3 and complement binding assays\",\n      \"pmids\": [\"38710711\", \"39302131\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The identity of the terminal glucose transferase enzyme was defined only by phenotype in this corpus\", \"Mechanism by which the side chain restrains virulence via CD36/galectin-3 not fully resolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the two GalNAc glycoforms of the GPI anchor are sorted between protein anchoring and free surface glycolipid, and the full contribution of individual ppGalNAc-T isoforms to specific in vivo substrates, remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular sorting machinery for GPI glycoforms unknown\", \"Isoform-specific acceptor-site rules in vivo incompletely defined\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0004653\", \"supporting_discovery_ids\": [2, 3, 4, 8, 11], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0016758\", \"supporting_discovery_ids\": [4, 11, 12], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0046872\", \"supporting_discovery_ids\": [11], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005789\", \"supporting_discovery_ids\": [6, 7], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0009986\", \"supporting_discovery_ids\": [5], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0045121\", \"supporting_discovery_ids\": [5], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0006506\", \"supporting_discovery_ids\": [0, 1, 5, 6, 7, 12], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0006493\", \"supporting_discovery_ids\": [2, 3, 4, 8, 9, 10], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CST1 (cyst wall mucin-like glycoprotein, O-GalNAc substrate of ppGalNAc-T2/T3)\",\n      \"SRS13 (mucin-domain SRS protein, O-GalNAc substrate of ppGalNAc-T2/T3)\",\n      \"SAG1/P30 (GPI-anchored surface protein bearing core GalNAc glycoforms)\",\n      \"CD36 (host scavenger receptor bound by GIPLs, modulated by PIGJ side chain)\",\n      \"galectin-3 (host lectin binding GIPLs, modulated by PIGJ side chain)\"\n    ],\n    \"other_free_text\": [\n      \"GalNAc modification operates in two distinct T. gondii pathways: GPI anchor Glcα1-4GalNAcβ1-4 side-chain biosynthesis (PIGJ plus a terminal glucose transferase) and mucin-type O-glycosylation (ppGalNAc-T family).\",\n      \"Only GPIs bearing the terminal Glc on GalNAc are immunogenic; PIGJ deletion abolishing the side chain increases virulence and enhances CD36 and galectin-3 binding.\",\n      \"Core GalNAc is added to the free GPI precursor after inositol deacylation and before transfer to protein.\",\n      \"ppGalNAc-T2 initiates and ppGalNAc-T3 follows up hierarchical O-glycosylation of cyst wall glycoproteins, required for brain cyst structural rigidity.\",\n      \"ppGalNAc-T3 possesses a unique second catalytic metal ion coupled to substrate binding and required for cyst wall O-glycosylation, diverging from host homologues.\"\n    ]\n  },\n  \"strain_conflicts\": []\n}","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_259530","name":null,"product":"GalNac","uniprot_acc":"A0A125YXQ0","chromosome":"TGME49_chrVIIb","start_pos":2782826},{"strain":"GT1","gene_id":"TGGT1_259530","name":null,"product":"GalNac","uniprot_acc":null,"chromosome":"TGGT1_chrVIIb","start_pos":2759031},{"strain":"RH88","gene_id":"TGRH88_070610","name":null,"product":"GalNac","uniprot_acc":null,"chromosome":"CM023089","start_pos":2804746},{"strain":"VEG","gene_id":"TGVEG_259530","name":null,"product":"GalNac","uniprot_acc":"B6KBG3","chromosome":"TGVEG_chrVIIb","start_pos":2802250}]}