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Structural analysis of human Cdc20 supports multisite degron recognition by APC/C.


ABSTRACT: The anaphase-promoting complex/cyclosome (APC/C) promotes anaphase onset and mitotic exit through ubiquitinating securin and cyclin B1. The mitotic APC/C activator, the cell division cycle 20 (Cdc20) protein, directly interacts with APC/C degrons--the destruction (D) and KEN boxes. APC/C(Cdc20) is the target of the spindle checkpoint. Checkpoint inhibition of APC/C(Cdc20) requires the binding of a BubR1 KEN box to Cdc20. How APC/C recognizes substrates is not understood. We report the crystal structures of human Cdc20 alone or bound to a BubR1 KEN box. Cdc20 has a disordered N-terminal region and a C-terminal WD40 ? propeller with a preformed KEN-box-binding site at its top face. We identify a second conserved surface at the side of the Cdc20 ? propeller as a D-box-binding site. The D box of securin, but not its KEN box, is critical for securin ubiquitination by APC/C(Cdc20). Although both motifs contribute to securin ubiquitination by APC/C(Cdh1), securin mutants lacking either motif are efficiently ubiquitinated. Furthermore, D-box peptides diminish the ubiquitination of KEN-box substrates by APC/C(Cdh1), suggesting possible competition between the two motifs. Our results indicate the lack of strong positive cooperativity between the two degrons of securin. We propose that low-cooperativity, multisite target recognition enables APC/C to robustly ubiquitinate diverse substrates and helps to drive cell cycle oscillations.

SUBMITTER: Tian W 

PROVIDER: S-EPMC3494910 | BioStudies | 2012-01-01

REPOSITORIES: biostudies

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