Affinage · Toxoplasma gondii

TGME49_257680

myosin light chain MLC1 · UniProt A0A125YYD4

Annotated
2026-09-08
17 papers in source corpus 15 papers cited in narrative 15 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TgMLC1 is a regulatory light chain of the Toxoplasma gondii class XIV myosin TgMyoA and a core component of the glideosome, the pellicle-anchored actomyosin motor that powers gliding motility, substrate attachment, and host cell invasion (PMID:11980712, PMID:15123738). It clamps around the helical MyoA neck (IQ-motif region, residues 775–818) with a bilobed architecture and ~10 nM affinity, and its prebinding cooperatively enhances recruitment of the essential light chain ELC1 to the same neck, supporting a staged lever-arm assembly (PMID:28972141). Within the assembled motor, MLC1 together with ELC1 stabilizes the lever arm to enable fast actin sliding, with the two light chains more than doubling actin gliding speed relative to MyoA alone (PMID:25231988). The MLC1-MyoA complex assembles into a four-protein glideosome with GAP45 and the IMC-anchored integral membrane glycoprotein GAP50, GAP45 bridging the soluble MyoA-MLC1 module to the inner membrane complex (PMID:15123738, PMID:20951968). MLC1 is palmitoylated on N-terminal cysteines C8 and C11, a modification required for MLC1-GAP45 binding but largely dispensable for gliding (PMID:34011689), and covalent modification of C58 by the small-molecule inhibitor tachypleginA-2 reduces motor activity (PMID:24892871, PMID:20084115). Conditional depletion of MLC1 halves motor speed and impairs but does not abolish gliding and invasion, with a specific requirement for substrate attachment under flow rather than for movement initiation per se (PMID:24632839, PMID:28100223).

Mechanistic history

Synthesis pass · year-by-year structured walk · 14 steps
  1. 2002 High

    Establishing that TgMLC1 is a bona fide myosin light chain answered whether Toxoplasma possesses a defined fast motor complex, showing MyoA-MLC1 is a single-headed, plus-end-directed motor with measurable mechanics.

    Evidence In vitro motility assay and microneedle-laser trap on purified motor complex

    PMID:11980712

    Open questions at the time
    • Did not resolve MLC1's structural mode of binding to MyoA
    • Role of additional light chains not yet defined
  2. 2004 High

    Defining the glideosome as a four-protein IMC-localized complex answered how the soluble motor is physically coupled to the parasite pellicle, identifying GAP50 as the membrane anchor and a spatially staged assembly.

    Evidence Reciprocal co-immunoprecipitation, subcellular fractionation, and IF/EM localization

    PMID:15123738

    Open questions at the time
    • Molecular triggers controlling assembly stages not defined
    • MLC1's individual contribution to anchoring not isolated
  3. 2009 Medium

    Linking MLC1 to the vesicular GTPase Rab11A extended its role beyond force generation, connecting the motor to IMC maturation and membrane delivery during daughter cell formation.

    Evidence Co-immunoprecipitation, conditional dominant-negative expression, live imaging

    PMID:19165333

    Open questions at the time
    • Direct vs. indirect nature of MLC1-Rab11A association not resolved
    • Single-lab Co-IP association
  4. 2010 High

    Mapping GAP45 as the recruiter of the MLC1-MyoA module to the IMC clarified how the motor is targeted and how pellicle integrity is preserved during invasion.

    Evidence Conditional knockdown, reciprocal Co-IP, and complementation assays

    PMID:20951968

    Open questions at the time
    • Exact MLC1 residues contacting GAP45 not defined here
    • Distinction between structural anchoring and force transduction unresolved
  5. 2010 High

    Demonstrating that a small-molecule-induced PTM on MLC1 (Val46-Arg59 region) lowers motor activity showed that MLC1 covalent modification can directly modulate class XIV myosin mechanics.

    Evidence In vitro motility assay on complexes from treated parasites, peptide mass mapping

    PMID:20084115

    Open questions at the time
    • Precise modified residue not pinpointed in this study
    • Physiological equivalent of the induced PTM unknown
  6. 2011 Medium

    Identifying Ca2+-dependent phosphorylation of multiple MLC1 residues addressed whether calcium signaling regulates the motor, correlating these marks with invasion-associated motor activity.

    Evidence SILAC quantitative LC-MS/MS and 32P labeling in Ca2+-stimulated tachyzoites

    PMID:21980283

    Open questions at the time
    • Link to activity is correlative
    • Kinase(s) responsible not identified
  7. 2014 High

    Reconstituting the motor from heterologous subunits established that MLC1 and ELC1 together stabilize the lever arm for fast motility and that the TgUNC co-chaperone is needed for functional assembly.

    Evidence Baculovirus/Sf9 expression, in vitro actin gliding assay with defined light chain combinations

    PMID:25231988

    Open questions at the time
    • Structural basis of the ELC1-MLC1 cooperativity not resolved here
    • In vivo relevance of the speed increment not tested
  8. 2014 Medium

    Conditional depletion showed MLC1 is important but not strictly essential, defining a quantitative rather than absolute requirement for gliding and invasion.

    Evidence Tet-regulatable conditional knockout with gliding and invasion assays

    PMID:24632839

    Open questions at the time
    • Residual motility source not defined
    • Single-lab phenotype
  9. 2014 Medium

    Testing all mapped phospho-mutants established that MLC1 phosphorylation is dispensable for glideosome assembly and motility, dissociating the Ca2+-dependent marks from essential motor function.

    Evidence Site-directed phospho-mimetic/phospho-null allelic replacement with motility and Co-IP readouts

    PMID:24779470

    Open questions at the time
    • Negative result; subtle or combinatorial phospho-roles not excluded
    • Does not address non-motility phenotypes
  10. 2014 High

    Identifying MLC1 C58 as the covalent target of tachypleginA-2 pinpointed a functionally relevant, druggable residue whose modification impairs motility.

    Evidence Click chemistry, MS adduct mapping, C58S knock-in, 3D motility assay

    PMID:24892871

    Open questions at the time
    • Structural mechanism by which C58 modification impairs the lever arm not resolved
    • Single-lab
  11. 2015 Medium

    Placing MLC1 at one of two adjacent IQ light chain sites and modeling a Ca2+-promoted ELC-MLC1 interface addressed how the light chains cooperate to stabilize the lever arm, with interface mutations degrading gliding.

    Evidence Molecular dynamics simulation, interface mutagenesis, gliding assay, conditional knockdown

    PMID:26374117

    Open questions at the time
    • Interface is simulation-inferred, not directly resolved
    • Direct Ca2+-binding role not experimentally confirmed
  12. 2017 High

    The 1.85 A crystal structure of MLC1 on the MyoA neck resolved its bilobed clamping architecture, quantified ~10 nM binding, and showed MLC1 prebinding boosts ELC1 affinity 8-fold, providing the structural basis for staged cooperative assembly.

    Evidence X-ray crystallography, HDX-MS, and isothermal titration calorimetry

    PMID:28972141

    Open questions at the time
    • Full-length assembled motor structure with ELC1/2 not captured
    • Conformational changes during force generation not visualized
  13. 2017 Medium

    Conditional depletion under flow revealed MLC1 is specifically required for substrate attachment, not for initiating 3D movement, refining its functional role within the actomyosin system.

    Evidence mlc1 conditional KO with 3D motility and collagen-substrate attachment assays under flow

    PMID:28100223

    Open questions at the time
    • Molecular link between the motor and adhesin traction not defined
    • Single-lab
  14. 2021 High

    Mapping palmitoylation to C8/C11 and showing it is required for MLC1-GAP45 binding yet dispensable for gliding challenged the assumption that the MLC1-GAP45 link is essential for force transduction.

    Evidence C8/C11 mutagenesis, palmitoylation and Co-IP assays, motility assays

    PMID:34011689

    Open questions at the time
    • How the motor remains functional without the GAP45 link not resolved
    • Alternative anchoring route not identified

Open questions

Synthesis pass · forward-looking unresolved questions
  • How MLC1-dependent lever-arm mechanics are physically coupled to surface adhesins to produce substrate traction, and how the motor stays functional when its GAP45 anchoring is lost, remain unresolved.
  • No structure of the fully assembled, membrane-anchored glideosome
  • Mechanism connecting motor force to attachment not defined
  • Kinase and functional consequence of Ca2+-dependent phosphorylation unresolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
RAB11ATGELC1 (ESSENTIAL LIGHT CHAIN)TGELC2TGGAP40TGGAP45TGGAP50TGMYOA (MYOSIN A HEAVY CHAIN, IQ-MOTIF NECK, ~10 NM)TGUNC (CO-CHAPERONE REQUIRED FOR ASSEMBLY)
Complex memberships
Glideosome motor complex (MyoA-MLC1-GAP45-GAP50, with GAP40)MyoA-MLC1-ELC1 tripartite motor module

Evidence

Reading pass · 15 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2002 TgMLC1 is a novel myosin light chain that binds TgMyoA; the TgMyoA-TgMLC1 motor complex is a fast, single-headed, plus-end-directed motor moving in unitary steps of 5.3 nm at 5.2 µm/s toward the plus end of actin filaments, as established by microneedle-laser trap and sliding velocity assays. In vitro motility assay, microneedle-laser trap, biochemical characterization of purified motor complex The EMBO journal High 11980712
2004 TgMLC1 is a component of a four-protein complex with TgMyoA, TgGAP45, and TgGAP50 that localizes to the inner membrane complex (IMC); this complex is anchored to the IMC via TgGAP50, an integral membrane glycoprotein; assembly occurs in two stages and is spatially controlled. Co-immunoprecipitation, subcellular fractionation, localization by immunofluorescence/electron microscopy The Journal of cell biology High 15123738
2008 GAP45 phosphorylation at Ser163 and Ser167 controls the final assembly step of the myosin XIV motor complex: phospho-mimetic (Glu) mutations at these sites prevent association of the MyoA-MLC1-GAP45 soluble complex with membrane-anchored GAP50, while phospho-null (Ala) mutations do not affect complex assembly. Mass spectrometry identification of phosphorylation sites, site-directed mutagenesis (phospho-mimetic and phospho-null), co-immunoprecipitation Eukaryotic cell High 19047362
2009 TgMLC1 (MTIP) associates with Rab11A, a vesicular trafficking GTPase involved in IMC maturation and plasma membrane delivery during daughter cell formation; this interaction links the glideosome motor to Rab11A-mediated vesicular traffic required for completion of cytokinesis. Co-immunoprecipitation, conditional dominant-negative expression, live imaging PLoS pathogens Medium 19165333
2010 TgMLC1 is a component of the glideosome with GAP40, GAP45, GAP50, and MyoA; GAP45 C-terminal region recruits MLC1-MyoA to the IMC, while GAP45 N-terminal acylation and coiled-coil domain preserves pellicle integrity during invasion. Conditional knockdown, co-immunoprecipitation, complementation assays, immunofluorescence Cell host & microbe High 20951968
2010 Treatment with a small-molecule inhibitor induces a post-translational modification of TgMLC1 mapped to the peptide Val46-Arg59; myosin motor complexes containing modified TgMLC1 show significantly decreased in vitro motor activity, demonstrating that PTMs on TgMLC1 can modulate Class XIV myosin mechanical activity. In vitro motility assay with motor complexes from treated vs. control parasites, peptide mass mapping, 2D gel electrophoresis PLoS pathogens High 20084115
2011 SILAC-based quantitative phosphoproteomics identified calcium-dependent phosphorylation of multiple residues on MLC1 in live tachyzoites upon Ca²⁺-mobilizing drug stimulation; phosphorylation of these sites correlates with invasion motor activity. SILAC quantitative LC-MS/MS, ³²P labeling, 2D gel electrophoresis PLoS pathogens Medium 21980283
2014 TgMLC1 (as regulatory light chain) complexed with TgMyoA heavy chain moves actin at ~1.5 µm/s in an in vitro motility assay; addition of the essential light chain TgELC1 to the complex more than doubles actin sliding speed to ~3.4 µm/s, indicating MLC1 and ELC1 together stabilize the lever arm for fast motility. Co-expression with the T. gondii-specific co-chaperone TgUNC is required for functional motor assembly. Baculovirus/Sf9 heterologous expression, in vitro actin gliding assay, co-chaperone co-expression The Journal of biological chemistry High 25231988
2014 Conditional knockdown of MLC1 results in parasites with significantly reduced gliding motility and host cell invasion efficiency, but mutant parasites are not completely blocked and remain invasive, indicating MLC1 is important but not strictly essential for motility. Conditional knockout (Tet-regulatable), gliding motility assay, invasion assay PloS one Medium 24632839
2014 Phospho-mimetic and phospho-null mutations at all mapped TgMLC1 phosphorylation sites do not impact glideosome assembly or parasite motility, indicating TgMLC1 phosphorylation is not critical for glideosome function. Site-directed mutagenesis of phosphorylation sites, allelic replacement, motility assays, co-immunoprecipitation Cellular microbiology Medium 24779470
2014 TgMLC1 is identified as a direct and covalent target of the small-molecule inhibitor tachypleginA-2; the compound forms a covalent adduct (225.118 Da) on C58 of TgMLC1; the C58S knock-in mutation renders parasites less sensitive to the compound in motility assays, establishing C58 as the functionally relevant binding site. Click chemistry labeling, mass spectrometry adduct mapping, site-directed mutagenesis (C58S knock-in), 3D motility assay PloS one High 24892871
2015 MLC1 occupies one of two adjacent light chain binding sites on the MyoA neck (IQ motifs); molecular simulations indicate Ca²⁺ promotes intermolecular contacts between ELC1/ELC2 and the adjacent MLC1 to stabilize the lever arm; point mutations predicted to ablate ELC-MLC1 interface interactions reduce gliding quality, displacement, and speed. Molecular dynamics simulation, site-directed mutagenesis, gliding motility assay, conditional knockdown mBio Medium 26374117
2017 Crystal structure of MLC1 at 1.85 Å resolution in complex with the MyoA neck peptide reveals a bilobed architecture with MLC1 clamping around the helical MyoA peptide (residues 775–818); isothermal titration calorimetry measured a stable ~10 nM Kd for MLC1–MyoA peptide binding; prebinding of MLC1 to the MyoA neck enhances ELC1 affinity for the neck 8-fold, supporting a cooperative staged assembly model. X-ray crystallography (1.85 Å), hydrogen-deuterium exchange mass spectrometry, isothermal titration calorimetry The Journal of biological chemistry High 28972141
2017 Conditional knockdown of MLC1 results in parasites that can still initiate 3D movement at wildtype speeds but are virtually unable to attach to collagen-coated substrates under flow conditions, demonstrating that MLC1 (and the actomyosin system) is specifically required for substrate attachment rather than solely for force generation during motility. Conditional knockout (mlc1 cKO), 3D motility assay, substrate attachment assay under flow conditions BMC biology Medium 28100223
2021 TgMLC1 is palmitoylated on two N-terminal cysteine residues, C8 and C11; mutations blocking palmitoylation completely abrogate binding of TgMLC1 to TgGAP45, yet these palmitoylation-deficient mutant parasites show little impact on gliding motility, challenging the model that MLC1-GAP45 interaction is essential for force transduction. Site-directed mutagenesis (C8/C11 mutations), palmitoylation assay, co-immunoprecipitation, motility assays mSphere High 34011689

Source papers

Stage 0 corpus · 17 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2010 Functional dissection of the apicomplexan glideosome molecular architecture. Cell host & microbe 234 20951968
2004 Identification of the membrane receptor of a class XIV myosin in Toxoplasma gondii. The Journal of cell biology 214 15123738
2002 Toxoplasma gondii myosin A and its light chain: a fast, single-headed, plus-end-directed motor. The EMBO journal 197 11980712
2009 Rab11A-controlled assembly of the inner membrane complex is required for completion of apicomplexan cytokinesis. PLoS pathogens 95 19165333
2014 The toxoplasma Acto-MyoA motor complex is important but not essential for gliding motility and host cell invasion. PloS one 91 24632839
2017 Surface attachment, promoted by the actomyosin system of Toxoplasma gondii is important for efficient gliding motility and invasion. BMC biology 81 28100223
2011 Quantitative in vivo analyses reveal calcium-dependent phosphorylation sites and identifies a novel component of the Toxoplasma invasion motor complex. PLoS pathogens 73 21980283
2008 GAP45 phosphorylation controls assembly of the Toxoplasma myosin XIV complex. Eukaryotic cell 65 19047362
2015 Two Essential Light Chains Regulate the MyoA Lever Arm To Promote Toxoplasma Gliding Motility. mBio 40 26374117
2010 A small-molecule inhibitor of T. gondii motility induces the posttranslational modification of myosin light chain-1 and inhibits myosin motor activity. PLoS pathogens 39 20084115
2014 A Toxoplasma gondii class XIV myosin, expressed in Sf9 cells with a parasite co-chaperone, requires two light chains for fast motility. The Journal of biological chemistry 36 25231988
2011 Unusual anchor of a motor complex (MyoD-MLC2) to the plasma membrane of Toxoplasma gondii. Traffic (Copenhagen, Denmark) 28 21143563
2014 Assessment of phosphorylation in Toxoplasma glideosome assembly and function. Cellular microbiology 25 24779470
2017 Dissecting the molecular assembly of the Toxoplasma gondii MyoA motility complex. The Journal of biological chemistry 16 28972141
2014 Identification of T. gondii myosin light chain-1 as a direct target of TachypleginA-2, a small-molecule inhibitor of parasite motility and invasion. PloS one 16 24892871
2021 Blocking Palmitoylation of Toxoplasma gondii Myosin Light Chain 1 Disrupts Glideosome Composition but Has Little Impact on Parasite Motility. mSphere 11 34011689
2016 [Research Advances on Gliding-associated Proteins of Toxoplasma gondii]. Zhongguo ji sheng chong xue yu ji sheng chong bing za zhi = Chinese journal of parasitology & parasitic diseases 0 30130043