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/CCdc20 is the target of the spindle checkpoint. Checkpoint inhibition of APC/CCdc20 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 β propeller with a preformed KEN-box-binding site at its top face. We identify a second conserved surface at the side of the Cdc20 β propeller as a D-box-binding site. The D box of securin, but not its KEN box, is critical for securin ubiquitination by APC/CCdc20. Although both motifs contribute to securin ubiquitination by APC/CCdh1, 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.
Original language | English (US) |
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Pages (from-to) | 18419-18424 |
Number of pages | 6 |
Journal | Proceedings of the National Academy of Sciences of the United States of America |
Volume | 109 |
Issue number | 45 |
DOIs | |
State | Published - Nov 6 2012 |
Keywords
- Crystallography
- Mitosis
- Molecular recognition
- Multivalency
ASJC Scopus subject areas
- General