DHHC3

DHHC3 (PF3D7_1121000) is a palmitoyl transferase that mediates gliding motility and mosquito-to-vertebrate transmission across the Plasmodium life cycle, characterized largely through its P. berghei ortholog (PMID:27084458). It localizes to the inner membrane complex (IMC) of ookinetes (PMID:27084458), the structure underlying motility in invasive stages. Genetic deletion in P. berghei severely impairs gliding motility in both ookinetes and sporozoites, renders ookinetes poorly infectious to mosquitoes, and leaves sporozoites non-infectious to mice; genetic complementation fully restores virulence, establishing DHHC3 as a causal mediator of these phenotypes (PMID:27084458). DHHC3 shares partial functional redundancy with the related palmitoyl transferase DHHC9, as a DHHC3/DHHC9 double knockout produces an enhanced phenotype relative to either single knockout (PMID:27084458). Beyond its IMC localization, motility requirement, and functional overlap with DHHC9, the specific protein substrates palmitoylated by DHHC3 have not been defined in the available corpus.

1. 2016 Medium

   Establishing where a candidate palmitoyl transferase acts was the first step: DHHC3 was shown to occupy the inner membrane complex of ookinetes, placing it at the motility apparatus.

   Evidence Gene tagging and fluorescence co-localization with an IMC marker in P. berghei ookinetes

   PMID:27084458

   Open questions at the time

   • Localization shown in ookinetes but not resolved across all invasive stages
   • No identification of which IMC proteins DHHC3 associates with or palmitoylates
2. 2016 High

   Whether DHHC3 is functionally required was answered by deletion: loss abolishes gliding motility and blocks transmission at two life-cycle transitions, with complementation confirming causality.

   Evidence Gene knockout with gliding motility assay, mosquito and mouse infectivity assays, and genetic complementation in P. berghei

   PMID:27084458

   Open questions at the time

   • The palmitoylation substrates whose modification drives motility are not identified
   • Mechanistic link between palmitoyl transferase activity and IMC/motor function not established
   • Direct demonstration of enzymatic activity for the P. berghei ortholog not shown
3. 2016 Medium

   Genetic epistasis addressed whether DHHC3 acts alone: a DHHC3/DHHC9 double knockout exceeds either single knockout, revealing partial functional overlap between the two palmitoyl transferases.

   Evidence Double gene deletion with phenotypic comparison to single knockouts in P. berghei

   PMID:27084458

   Open questions at the time

   • Shared substrates between DHHC3 and DHHC9 not defined
   • Degree and molecular basis of the redundancy not characterized
4. 2016 Low

   In a parallel P. falciparum survey of the DHHC family, PfDHHC3 (PF3D7_1121000) localization was characterized within a set where multiple DHHC enzymes palmitoylate the same substrate in vitro, hinting at redundancy, though substrate assignments specific to PfDHHC3 were not resolved.

   Evidence In vitro palmitoyl-transferase assays, endogenous tagging localization, and knockout studies across the PfDHHC family in P. falciparum

   PMID:27060339

   Open questions at the time

   • The abstract treats the DHHC family broadly and does not isolate which findings apply specifically to PF3D7_1121000
   • No substrate uniquely assigned to PfDHHC3
   • Enzymatic activity of PfDHHC3 not individually demonstrated

• The direct palmitoylation substrates of DHHC3 and the molecular pathway connecting its enzymatic activity to gliding motility remain unidentified.
• No DHHC3-specific substrate identified
• No structural or biochemical model of DHHC3 activity in Plasmodium
• Mechanism of DHHC3/DHHC9 redundancy at the substrate level unknown