CDC50B

CDC50B (PF3D7_1133300) is a P4-ATPase beta-subunit/chaperone that functions within the guanylyl cyclase alpha (GCα) membrane signaling platform of Plasmodium blood and sexual stages (PMID:35862778, PMID:37327340). In P. falciparum asexual blood stages, CDC50B is expressed and binds GCα directly, and this interaction supports optimal cGMP synthesis to set the rate of merozoite egress, although CDC50B is dispensable for intraerythrocytic maturation (PMID:35862778). This association with GCα is conserved across life-cycle stages in P. berghei, where CDC50B is recovered with GCα from both gametocytes and schizonts but is excluded from UGO-containing immunoprecipitates, placing it in a distinct sub-complex of the platform (PMID:37327340). Consistent with a lipid-flippase cofactor role, the P. chabaudi orthologue co-purifies with the P4-ATPase PcATP2 as a complex whose ATPase activity is stimulated by phosphatidylserine or phosphatidylethanolamine and further enhanced by phosphatidylinositol 4-phosphate (PMID:33372863). Beyond these findings, the structural basis of CDC50B–partner recognition and its precise contribution to cGMP signaling remain uncharacterized in the available corpus.

1. 2021 High

   Whether a Plasmodium CDC50B-containing complex possesses lipid-transport enzymatic activity was unknown; reconstituting the orthologue with a P4-ATPase established it as a functional lipid-flippase cofactor.

   Evidence recombinant expression, co-purification, and in vitro ATPase assays of the PcATP2/PcCdc50B complex in P. chabaudi

   PMID:33372863

   Open questions at the time

   • Direct lipid translocation (flipping) was inferred from ATPase stimulation rather than measured directly
   • Whether the P. falciparum CDC50B pairs with the same or a different P4-ATPase in vivo is not established
   • No structural model of the CDC50B/P4-ATPase interface
2. 2022 High

   The in vivo binding partner and blood-stage role of CDC50B were undefined; tagging, conditional disruption, and Co-IP identified GCα as a direct partner and linked CDC50B to the timing of merozoite egress via cGMP synthesis.

   Evidence gene tagging, conditional gene disruption, and co-immunoprecipitation in P. falciparum asexual blood stages

   PMID:35862778

   Open questions at the time

   • How CDC50B binding to GCα mechanistically enhances cGMP output is not defined
   • CDC50B is not essential, leaving its non-redundant contribution unclear
   • Whether its flippase activity is functionally coupled to GCα regulation is not tested
3. 2023 Medium

   Whether the CDC50B–GCα association extends beyond asexual stages and how it is organized within the larger signaling platform were open; affinity purification across stages showed conservation and defined CDC50B as part of a sub-complex distinct from UGO.

   Evidence cross-linking affinity purification/mass spectrometry from P. berghei gametocytes and schizonts

   PMID:37327340

   Open questions at the time

   • The functional consequence of CDC50B exclusion from the UGO sub-complex is unknown
   • Stoichiometry and architecture of the GCα platform are not resolved
   • No functional (loss-of-function) test of CDC50B was performed in P. berghei

• It remains unknown how CDC50B's lipid-flippase cofactor activity is mechanistically integrated with its role in the GCα platform to control cGMP synthesis and egress timing.
• No structure of CDC50B or its complexes
• Direct link between flippase activity and cGMP regulation untested
• Membrane lipid environment required for GCα activation not defined