PF3D7_0111000

Plasmodium kinesin-8B (PF3D7_0111000) is a microtubule-based motor whose function is dedicated to male gamete development during the parasite's sexual stage (PMID:31409625, PMID:31634979). It is expressed specifically during male gametogenesis and localizes dynamically to cytoplasmic basal bodies and the assembling axoneme, and notably does not co-localize with nuclear kinetochores, distinguishing it from mitotic spindle motors (PMID:31409625, PMID:31634979). At the basal body it co-localizes with the outer centriolar MTOC component SAS4 rather than with kinetochore machinery (PMID:35550346). Functionally, its motor domain is bifunctional: reconstituted P. berghei and P. falciparum motor domains drive both ATP-dependent microtubule gliding and ATP-dependent microtubule depolymerisation, and cryo-EM reveals Plasmodium-distinct residues at the microtubule interface together with a non-canonical neck-linker mechanism that does not dock upon ATP-analogue binding yet is required for both activities (PMID:36384964). Genetic ablation in P. berghei leaves intranuclear mitosis and the three rounds of genome replication intact but specifically disrupts 9+2 axoneme assembly and flagellum formation—cytoplasmic microtubules assemble as doublets and elongate but fail to organize into a proper axoneme—blocking microgamete assembly and completely abolishing transmission to the mosquito (PMID:31409625, PMID:31634979).

1. 2019 High

   Establishing where kinesin-8B acts settled whether it functions in mitosis or in a distinct cytoplasmic process, revealing a role in axoneme rather than spindle biology.

   Evidence Live-cell imaging of GFP-tagged kinesin-8B with knockout and electron microscopy in P. berghei

   PMID:31409625 PMID:31634979

   Open questions at the time

   • Does not resolve which axonemal microtubule populations the motor physically engages
   • Recruitment mechanism to the basal body not defined
2. 2019 High

   Loss-of-function defined the essential cellular requirement for kinesin-8B, showing it is specifically required for 9+2 axoneme/flagellum formation and thus for transmission.

   Evidence Gene knockout (ΔPbkin8B), ultrastructural EM, and mosquito transmission assays in P. berghei

   PMID:31409625 PMID:31634979

   Open questions at the time

   • Does not explain mechanistically why doublet microtubules elongate but fail to form the 9+2 pattern
   • Whether the phenotype is conserved in P. falciparum not directly tested in vivo
3. 2022 High

   Biochemical and structural reconstitution answered what the motor actually does at the molecular level, defining it as a bifunctional gliding/depolymerising motor with a non-canonical neck-linker mechanism.

   Evidence In vitro microtubule gliding and depolymerisation assays, cryo-EM of microtubule-bound motor domains, and neck-linker mutagenesis for both P. berghei and P. falciparum motor domains

   PMID:36384964

   Open questions at the time

   • How gliding versus depolymerisation activity is deployed during axoneme assembly in vivo is unresolved
   • Functional impact of the Plasmodium-distinct interface residues in living gametocytes not tested
4. 2022 Medium

   Co-localization with a basal body marker refined the subcellular assignment, placing kinesin-8B at the cytoplasmic outer centriolar MTOC rather than the nuclear MTOC.

   Evidence Fluorescence co-localization of kinesin-8B with SAS4 (and exclusion from NDC80/kinetochore), with SAS4 gene deletion and EM in P. berghei

   PMID:35550346

   Open questions at the time

   • Kinesin-8B served as a reference marker and was not functionally interrogated in this study
   • Direct physical interaction between kinesin-8B and SAS4 not demonstrated

• How kinesin-8B is recruited to the basal body and how its dual gliding/depolymerase activities are spatiotemporally coordinated to build the 9+2 axoneme in vivo remains unresolved.
• No identified recruitment factor or direct binding partner for kinesin-8B
• In vivo relevance of depolymerisation versus gliding activity to axoneme patterning not established