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  • Title: Cryo-EM of Mitotic Checkpoint Complex-Bound APC/C Reveals Reciprocal and Conformational Regulation of Ubiquitin Ligation.
    Author: Yamaguchi M, VanderLinden R, Weissmann F, Qiao R, Dube P, Brown NG, Haselbach D, Zhang W, Sidhu SS, Peters JM, Stark H, Schulman BA.
    Journal: Mol Cell; 2016 Aug 18; 63(4):593-607. PubMed ID: 27522463.
    Abstract:
    The mitotic checkpoint complex (MCC) coordinates proper chromosome biorientation on the spindle with ubiquitination activities of CDC20-activated anaphase-promoting complex/cyclosome (APC/C(CDC20)). APC/C(CDC20) and two E2s, UBE2C and UBE2S, catalyze ubiquitination through distinct architectures for linking ubiquitin (UB) to substrates and elongating polyUB chains, respectively. MCC, which contains a second molecule of CDC20, blocks APC/C(CDC20)-UBE2C-dependent ubiquitination of Securin and Cyclins, while differentially determining or inhibiting CDC20 ubiquitination to regulate spindle surveillance, checkpoint activation, and checkpoint termination. Here electron microscopy reveals conformational variation of APC/C(CDC20)-MCC underlying this multifaceted regulation. MCC binds APC/C-bound CDC20 to inhibit substrate access. However, rotation about the CDC20-MCC assembly and conformational variability of APC/C modulate UBE2C-catalyzed ubiquitination of MCC's CDC20 molecule. Access of UBE2C is limiting for subsequent polyubiquitination by UBE2S. We propose that conformational dynamics of APC/C(CDC20)-MCC modulate E2 activation and determine distinctive ubiquitination activities as part of a response mechanism ensuring accurate sister chromatid segregation.
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