The anaphase-promoting complex (APC/C) is a large multi-subunit complex (~1.2 MDa) that functions to regulate cell cycle transitions, specifically the metaphase to anaphase transition in mitosis (when duplicated sister chromatid pairs are separated), the exit from mitosis and maintenance of G1. The APC/C regulates these processes by targeting specific cell cycle proteins (for example cyclins and securin) for proteolysis by the ubiquitin-proteosome system (UPS). The role of the APC/C is to recognise substrates through degrons (D box and KEN box) and assemble a poly-ubiquitin chain of defined linkage onto its substrates. The poly-ubiquitin chain functions as a signal for recognition by the proteasome.

The APC/C is regulated by the mitotic checkpoint that ensures that chromosome segregation is coordinated with the correct attachment of chromosomes to the mitotic spindle. Failure of the mitotic checkpoint causes chromosome mis-segregation and aneuploidy. Other regulatory mechanisms, including activation by co-activator subunits and protein phosphorylation, also determine APC/C activity and substrate specificity.

Atomic model of the anaphase-promoting complex/cyclosome (APC/C) determined using cryo-EM.

The aims of our research are to understand the molecular mechanisms underlying the assembly of this large complex, its capacity to recognize and ubiquitinate proteins in a cell cycle-coordinated manner, and the structural basis for its control by the spindle assembly checkpoint.

To pursue these aims we use a combination of protein crystallography and single particle electron cryo-microscopy of defined reconstituted complexes.