MLC2

MLC2 is a coccidian-specific myosin light chain of Toxoplasma gondii that functions as a regulatory subunit of a plasma-membrane-anchored motor complex (PMID:21143563). It associates with myosin D (MyoD) through its calmodulin-like domain, forming a MyoD-MLC2 motor complex, and is targeted to the parasite plasma membrane by its N-terminal extension (PMID:21143563). Beyond this association and membrane-anchoring role, the enzymatic mechanism and functional consequences of the complex have not been characterized in the available corpus.

1. 2011 Medium

   Establishing whether an unassigned calmodulin-like protein partners with a specific myosin defined MLC2 as the light chain of a discrete MyoD motor complex at the parasite plasma membrane.

   Evidence subcellular localization, protein-protein association, and molecular modeling in T. gondii

   PMID:21143563

   Open questions at the time

   • the compact complex architecture rests on modeling, not an experimentally solved structure
   • the functional role of the MyoD-MLC2 complex in parasite biology (e.g. motility, invasion) was not tested
2. 2011 Low

   Comparative genomics addressed how phylogenetically widespread this light chain is, showing MLC2 is restricted to coccidians and absent from other apicomplexans such as Plasmodium.

   Evidence bioinformatic survey of calmodulin-like proteins across Apicomplexa combined with experimental localization

   PMID:21143563

   Open questions at the time

   • coccidian restriction is a sequence-based inference; no functional experiment tests the mechanistic consequence of this lineage restriction
3. 2011 Low

   To explain how MLC2 reaches the plasma membrane, sequence/modeling analysis identified palmitoylation of its N-terminal extension as the likely membrane anchor.

   Evidence sequence analysis and molecular modeling predicting palmitoylation sites in T. gondii

   PMID:21143563

   Open questions at the time

   • palmitoylation is inferred from prediction; direct biochemical demonstration of lipid modification was not reported
   • the palmitoyltransferase and whether the modification is required for membrane targeting are unknown

• The catalytic/mechanical output of the MyoD-MLC2 complex and its role in parasite motility, invasion, or replication remain undefined.
• no genetic knockout or knockdown phenotype
• no direct demonstration of palmitoylation or its functional requirement
• no experimentally solved complex structure