Coactivator functions in a stoichiometric complex with anaphase-promoting complex/cyclosome to mediate substrate recognition.
The anaphase-promoting complex/cyclosome (APC/C) is a multisubunit E3 ligase required for ubiquitin-dependent proteolysis of cell-cycle-regulatory proteins, including mitotic cyclins and securin/Pds1. Regulation of APC/C activity and substrate recognition, mediated by the coactivators Cdc20 and Cdh1, is fundamental to cell-cycle control. However, the precise mechanism by which coactivators stimulate APC/C ubiquitylation activity and the nature of the substrate-binding sites on the activated APC/C are not understood. Here, we show that the optimal interaction of substrate with APC/C is dependent specifically on the simultaneous association of coactivator. This is consistent with a model whereby both core APC/C subunits and coactivators contribute recognition sites for substrates, accounting for the bipartite nature (D and KEN boxes) of most APC/C degradation signals. A direct and stoichiometric function for the coactivators could explain how specific substrates are recognized by APC/C in a cell-cycle-specific manner, and how coactivator stimulates APC/C ubiquitylation activity.
Passmore
Lori A
LA
Section of Structural Biology, The Institute of Cancer Research, 237 Fulham Road, London SW3 6JB, UK.
Barford
David
D
D064173:Anaphase-Promoting Complex-Cyclosome; D064199:Cdc20 Proteins; D064200:Cdh1 Proteins; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D008954:Models, Biological; D011485:Protein Binding; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D013379:Substrate Specificity; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism*; D015003:Yeasts
C577495:CDC20 protein, S cerevisiae; C577583:CDH1 protein, S cerevisiae; D064199:Cdc20 Proteins; D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins; D029701:Saccharomyces cerevisiae Proteins; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome