BCC4

BCC4 is a component of the Toxoplasma gondii basal complex, the ring-shaped structure at the basal end of the assembling daughter cytoskeleton, where it functions in cell division (PMID:35941170). BCC4 partners with MORN1 to form a 'rubber band' complex that sequesters the basal end of the budding daughter cytoskeleton, an interaction essential for successful division (PMID:35941170). Within the basal complex, BCC4 belongs to one of four architecturally distinct subcomplexes whose composition shifts dynamically in correlation with changing basal complex function during daughter budding (PMID:35941170). Beyond its assignment to a MORN1-associated subcomplex and its requirement for cell division, no further mechanistic detail—molecular activity, structural basis of the interaction, or regulatory inputs—has been characterized in the available corpus.

1. 2022 Medium

   It was unknown which proteins organize the basal end of the daughter cytoskeleton during Toxoplasma division; identifying that BCC4 and MORN1 form an essential 'rubber band' complex established a defined molecular module underlying basal complex constriction.

   Evidence Reciprocal proximity-based biotinylation (BioID) proteome mapping with disruption of component expression and cell division readouts in T. gondii

   PMID:35941170

   Open questions at the time

   • The direct biochemical nature of the BCC4-MORN1 interaction is not resolved by proximity labeling
   • No structural model of the 'rubber band' complex
   • The molecular activity of BCC4 itself is undefined
2. 2022 Medium

   It was unclear whether the basal complex is a single static assembly; placing BCC4 in one of four architecturally distinct, dynamically composed subcomplexes established that the basal complex is functionally compartmentalized and remodeled during budding.

   Evidence Reciprocal proximity-based biotinylation proteomics and spatiotemporal disruption experiments in T. gondii

   PMID:35941170

   Open questions at the time

   • The trigger and regulation of the compositional changes are not defined
   • The specific contribution of the BCC4-containing subcomplex to particular division steps is not isolated

• The molecular activity of BCC4, the structural basis of its interaction with MORN1, and the signals driving basal complex subcomplex remodeling remain unknown.
• No enzymatic or structural function assigned to BCC4
• Mechanism of subcomplex dynamic regulation uncharacterized
• No cross-strain or cross-species characterization in the corpus