PLC5

PLC5 (PF3D7_0627200, also detected as PfELC) is an essential light chain of the Plasmodium glideosome motor, the acto-myosin machinery that powers parasite motility and host-cell invasion (PMID:28978649, PMID:28893907). It co-purifies with the class XIV myosin PfMyoA as a second light chain and binds the MyoA neck region adjacent to the MTIP-binding site; this association is hierarchical, requiring MTIP to be bound to the MyoA heavy chain first, whereas MTIP itself binds independently of PLC5 (PMID:28978649, PMID:28893907). Functionally, co-assembly of PfMyoA with both PLC5 and MTIP maximizes MyoA-driven actin filament motility speed relative to MyoA with MTIP alone, consistent with PLC5 stabilizing and extending the myosin lever arm (PMID:28978649, PMID:28893907). In segmenting merozoites the protein co-localizes with MyoA and MTIP at the parasite periphery, placing it within the glideosome at the inner membrane complex (PMID:28893907). Beyond its role as a neck-binding light chain that tunes motor output, no further mechanistic detail for PLC5 has been characterized in the available corpus.

1. 2017 High

   Establishing that PfMyoA carries a second light chain beyond MTIP addressed whether the glideosome motor is a two-light-chain machine and defined the assembly order of its components.

   Evidence Affinity co-purification of PLC5 with PfMyoA from parasite lysates plus recombinant co-expression and in vitro binding assays (baculovirus/Sf9)

   PMID:28893907 PMID:28978649

   Open questions at the time

   • The structural basis of the MTIP-dependent binding hierarchy is not resolved
   • Whether PLC5 loss is tolerated in vivo (essentiality by genetic knockout) is not tested in these experiments
2. 2017 High

   Defining the neck-binding site and measuring motility with and without PLC5 answered how the second light chain contributes to motor function, showing it enhances actin gliding speed as expected for a lever-arm extension.

   Evidence In vitro actin gliding motility assays with recombinant PfMyoA co-expressed with MTIP and/or PLC5

   PMID:28893907 PMID:28978649

   Open questions at the time

   • The quantitative contribution of PLC5 to force output (not just speed) is not measured
   • A high-resolution structure of the PLC5–neck interface is absent from the corpus
3. 2017 Medium

   Localizing PLC5 to the parasite periphery in merozoites confirmed that the biochemically defined light chain physically resides within the glideosome at the inner membrane complex rather than elsewhere.

   Evidence Fluorescence immunolocalization across P. berghei life cycle stages

   PMID:28893907

   Open questions at the time

   • Localization was assessed in P. berghei; peripheral distribution in P. falciparum stages is not directly shown here
   • Dynamics of PLC5 recruitment during invasion are not resolved

• How PLC5 mechanically stiffens or extends the MyoA lever arm, and whether its function is genetically essential for invasion in vivo, remain unresolved.
• No high-resolution structure of the MyoA–MTIP–PLC5 assembly in the corpus
• No genetic knockout/conditional depletion establishing PLC5 essentiality for parasite motility or invasion
• Regulation of PLC5 assembly or its role outside the merozoite stage is uncharacterized