CRK5

TgCrk5 is a CDK-related kinase implicated in the regulation of chromosome replication and mitotic progression in Toxoplasma gondii tachyzoites (PMID:28830940). It localizes to the centrocone, the apicomplexan-specific spindle compartment of the nuclear envelope, during early S phase and displays a dynamic, cell cycle-regulated expression pattern that places it spatially at a key site of cell cycle control (PMID:28830940). At this location it forms a stable complex with ECR1, a 52-kDa protein bearing divergent RING and TRAF-Sina-like zinc-binding domains, with which it shares cell cycle expression dynamics and co-localization (PMID:28830940).

1. 2017 Medium

   Establishing where in the cell cycle machinery TgCrk5 acts, immunofluorescence placed it at the centrocone during early S phase, identifying it as a candidate regulator situated at the apicomplexan mitotic spindle compartment.

   Evidence Immunofluorescence microscopy with cell cycle staging in tachyzoites

   PMID:28830940

   Open questions at the time

   • Kinase activity and substrates at the centrocone not identified
   • Functional consequence of centrocone localization untested
   • Mechanism of recruitment to the centrocone unknown
2. 2017 Medium

   To identify TgCrk5's regulatory partners, co-IP/proteomics and colocalization revealed a stable complex with ECR1, linking the kinase to a putative E3 ligase and a mechanism controlling chromosome replication and mitosis.

   Evidence Co-immunoprecipitation/proteomics, immunofluorescence colocalization, and cell cycle expression analysis in T. gondii

   PMID:28830940

   Open questions at the time

   • ECR1 E3 ligase activity and its relationship to TgCrk5 phosphorylation not demonstrated
   • No reciprocal validation of the interaction reported
   • Whether TgCrk5 phosphorylates ECR1 or vice versa unknown