GPR180

GPR180 (PF3D7_1213500) is a plasma-membrane protein that acts as a stage-specific regulator of gametogenesis and mosquito transmission in Plasmodium, characterized entirely through its P. berghei ortholog PbGPR180 (PMID:35404079). It localizes to the plasma membrane of female gametes and ookinetes (PMID:35404079), and its deletion leaves asexual blood-stage growth intact while impairing gamete formation and reducing transmission to mosquitoes (PMID:35404079). Mechanistically, GPR180 functions upstream of the cGMP–PKG–Ca2+ signaling axis: loss of the gene lowers intracellular cGMP and delays and dampens cytosolic Ca2+ mobilization during gametocyte activation (PMID:35404079). In activated gametocytes the protein physically associates with transmembrane transporter proteins and the small GTPase Rab6 (PMID:35404079). Cross-species allele replacement with the P. vivax ortholog fully restores sexual development, establishing functional conservation of GPR180 across Plasmodium species (PMID:35404079). Beyond these findings, the biochemical activity by which GPR180 modulates cGMP levels has not been characterized in the available corpus.

1. 2022 Medium

   Establishing where GPR180 acts required knowing its subcellular home; localization to the plasma membrane of female gametes and ookinetes placed the protein at the parasite surface during sexual stages.

   Evidence Subcellular localization by immunofluorescence/live imaging of PbGPR180 in P. berghei

   PMID:35404079

   Open questions at the time

   • No orthogonal localization validation or membrane-topology mapping described
   • Localization in asexual stages and male gametes not resolved
2. 2022 Medium

   Whether GPR180 has an essential or stage-restricted role was unknown; a clean knockout showed asexual growth is unaffected but gamete formation and mosquito transmission are impaired, defining a sexual-stage-specific function.

   Evidence Genetic knockout of pbgpr180 in P. berghei with gamete formation and mosquito feeding assays

   PMID:35404079

   Open questions at the time

   • Does not distinguish male versus female gametocyte contributions
   • Molecular step within gametogenesis that fails is not defined
3. 2022 Medium

   To place GPR180 in a signaling pathway, the consequences of its loss on second messengers were measured; reduced cGMP and delayed/diminished Ca2+ mobilization positioned GPR180 upstream of the cGMP–PKG–Ca2+ cascade that drives gametocyte activation.

   Evidence cGMP quantification, Ca2+ mobilization measurement, and transcriptome analysis in knockout gametocytes of P. berghei

   PMID:35404079

   Open questions at the time

   • The direct biochemical activity linking GPR180 to cGMP production is not identified
   • Whether the effect on cGMP is direct or secondary to another defect is unresolved
4. 2022 Low

   Identifying binding partners was needed to hint at molecular function; co-immunoprecipitation revealed association with transmembrane transporters and the small GTPase Rab6 in activated gametocytes.

   Evidence Co-immunoprecipitation/pulldown in activated P. berghei gametocytes

   PMID:35404079

   Open questions at the time

   • Single interaction method without reciprocal validation described only in abstract
   • Functional significance of the Rab6 and transporter associations untested
   • Direct versus indirect nature of interactions unknown
5. 2022 Medium

   Whether GPR180 function is conserved across species was tested by cross-species complementation; the P. vivax ortholog fully rescued P. berghei sexual development, demonstrating functional conservation.

   Evidence Allele replacement of pbgpr180 with pvgpr180 in P. berghei

   PMID:35404079

   Open questions at the time

   • Conservation in the human parasite P. falciparum not directly demonstrated
   • Does not identify conserved functional residues or domains

• The molecular mechanism by which GPR180 modulates cGMP and how its transporter/Rab6 associations relate to signaling remain unknown, as does direct validation in P. falciparum.
• No enzymatic or receptor activity assigned to GPR180
• No structural model or topology
• No direct functional data on PF3D7_1213500 itself