Structural Biology

Marked for Destruction

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Science  25 May 2001:
Vol. 292, Issue 5521, pp. 1451
DOI: 10.1126/science.292.5521.1451b

One of the critical enzymatic mechanisms that regulates progression through cell division is the tagging and degradation of proteins. The anaphase-promoting complex (APC) functions as a ubiquitin ligase and attaches a small protein, ubiquitin, to those mitotic components, such as cyclins, that need to be destroyed. The ubiquitin tag serves as a signal that is recognized by the 26S proteasome, a large recycling center that digests proteins within a cylindrical reaction chamber. Gieffers et al. have prepared an 11-subunit 22–23S APC, which retains a ubiquitin-transferring activity and has a molecular mass of approximately 850,000. Visualization of these particles by cryoelectron microscopy revealed an asymmetric globular object of 135 angstroms in diameter. Substrate access to an internal cavity large enough to hold ubiquitin and the upstream ubiquitin-conjugating enzyme E2 could be dictated by regulatory factors. — GJC

Mol. Cell7, 907 (2001).

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