Abstract

The anaphase-promoting complex (APC) is an unusually large E3 ubiquitin ligase that controls defined cell cycle transitions such as the metaphase to anaphase transition and the exit from mitosis. Its activity and substrate specificity are regulated in a cell cycle-dependent manner by co-activator subunits, inhibitory protein complexes and reversible protein phosphorylation. To understand the molecular basis of APC function we have undertaken a structural analysis of different functional states of the complex through a combination of X-ray crystallography and single particle electron microscopy. Generation of a recombinant over-expression system that allowed reconstitution of the intact complex facilitated identification of individual APC subunits within the EM-derived molecular envelope, leading to the generation of pseudo-atomic models. I will describe our experimental approaches and how the resultant structures provide insights into APC architecture and mechanisms.