Emi2-mediated inhibition of E2-substrate ubiquitin transfer by the anaphase-promoting complex/cyclosome through a D-box-independent mechanism.
Vertebrate eggs are arrested at Metaphase II by Emi2, the meiotic anaphase-promoting complex/cyclosome (APC/C) inhibitor. Although the importance of Emi2 during oocyte maturation has been widely recognized and its regulation extensively studied, its mechanism of action remained elusive. Many APC/C inhibitors have been reported to act as pseudosubstrates, inhibiting the APC/C by preventing substrate binding. Here we show that a previously identified zinc-binding region is critical for the function of Emi2, whereas the D-box is largely dispensable. We further demonstrate that instead of acting through a "pseudosubstrate" mechanism as previously hypothesized, Emi2 can inhibit Cdc20-dependent activation of the APC/C substoichiometrically, blocking ubiquitin transfer from the ubiquitin-charged E2 to the substrate. These findings provide a novel mechanism of APC/C inhibition wherein the final step of ubiquitin transfer is targeted and raise the interesting possibility that APC/C is inhibited by Emi2 in a catalytic manner.
Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA.
Wanli
W
Tang
Judy Qiju
JQ
Wu
Chen
C
Chen
Chih-Sheng
CS
Yang
Jessie Yanxiang
JY
Guo
Christopher D
CD
Freel
Sally
S
Kornbluth
D020816:Amino Acid Motifs; D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D055162:Biocatalysis; D004789:Enzyme Activation; D044783:F-Box Proteins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D011485:Protein Binding; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D025801:Ubiquitin / Q000378:metabolism*; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism*; D043743:Ubiquitin-Protein Ligase Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014981:Xenopus / Q000378:metabolism*; D029867:Xenopus Proteins / Q000737:chemistry* / Q000378:metabolism*
D044783:F-Box Proteins; C498166:FBXO43 protein, Xenopus; D025801:Ubiquitin; D029867:Xenopus Proteins; D044763:Ubiquitin-Conjugating Enzymes; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome