DLC8a

TgDLC8a is a dynein light chain of Toxoplasma gondii that localizes specifically to the conoid at the parasite's apical end and functions in the apical secretory machinery required for host cell invasion (PMID:23233536, PMID:31206964). Unlike its orthologs in Eimeria, Plasmodium, or humans, conoid targeting is a unique feature of TgDLC8a (PMID:23233536). The protein forms a homodimer through β-strand swapping, in which each monomer's β strand pairs with the antiparallel β' strand of the opposing monomer to create two identical binding grooves suited for multitarget recognition, a structural arrangement distinct from the PfDLC8 homodimer (PMID:23233536). Phosphorylation at S88 controls this behavior: the phosphomimetic S88E mutation renders the protein monomeric and cytosolic, and its overexpression inhibits parasite growth, establishing that the dimeric, conoid-localized form is required for replication (PMID:23233536). Conditional depletion of DLC8a perturbs microneme exocytosis and disrupts apical docking of rhoptry organelles, and this dual defect produces a severe block in host cell invasion, with DLC8a acting at a step in the exocytosis cascade distinct from CEN2 (PMID:31206964).

1. 2012 Medium

   Establishing where TgDLC8a acts, its conoid localization at the apical end distinguished it from orthologs and pointed to a role specific to the T. gondii invasion apparatus.

   Evidence Subcellular localization imaging/fractionation and comparative analysis against Eimeria, Plasmodium, and human orthologs

   PMID:23233536

   Open questions at the time

   • Does not identify binding partners at the conoid
   • Mechanism of conoid targeting unknown
2. 2012 High

   The crystal structure resolved how TgDLC8a assembles, showing a β-strand-swapped homodimer with two identical grooves adapted for multitarget recognition and distinct from PfDLC8.

   Evidence Crystal structure determination and structural comparison

   PMID:23233536

   Open questions at the time

   • Cargo/target ligands occupying the binding grooves not identified
   • In vivo relevance of multitarget recognition untested
3. 2012 High

   Phosphorylation at S88 was shown to be a switch controlling oligomeric state and localization, and the dimeric conoid-bound form was shown to be required for replication.

   Evidence S88E phosphomimetic mutagenesis with in-parasite localization plus dominant-negative overexpression growth assay in human fibroblasts

   PMID:23233536

   Open questions at the time

   • Kinase responsible for S88 phosphorylation not identified
   • Whether S88 phosphorylation is regulated during the lytic cycle unknown
4. 2019 High

   Conditional depletion defined the cellular function, showing DLC8a is required for microneme exocytosis and apical rhoptry docking, and that loss produces a severe invasion defect at a step distinct from CEN2.

   Evidence Conditional knockdown with microneme secretion assays, rhoptry docking imaging, invasion assays, and epistatic comparison to CEN2

   PMID:31206964

   Open questions at the time

   • Molecular link between DLC8a and the secretory/docking machinery not defined
   • Direct binding partners mediating these functions unknown

• The direct cargo/partner ligands engaged by the two binding grooves, and the kinase that phosphorylates S88 to regulate dimer disassembly, remain unidentified.
• No identified binding partners at the conoid
• S88 kinase unknown
• Mechanistic connection between dimer state and secretion/docking undefined