Mechanism of Polyubiquitination by Human Anaphase-Promoting Complex: RING Repurposing for Ubiquitin Chain Assembly

• DOI: 10.1016/j.molcel.2014.09.009
• Publication Date: 2014-10-09T23:12:38Z
• Authors: Nicholas G. Brown; Edmond R. Watson; Florian Weissmann; Marc A. Jarvis; Ryan VanderLinden; Christy R.R. Grace; Jeremiah J. Frye; Renping Qiao; Prakash Dube; Georg Petzold; Shein Ei Cho; Omar Alsharif; Ju Bao; Iain F. Davidson; Jie J. Zheng; Amanda Nourse; Igor Kurinov; Jan-Michael Peters; Holger Stark; Brenda A. Schulman
• Keywords: Anaphase-promoting complex; Repurposing; Chain (unit); Ubiquitin-Protein Ligases

Polyubiquitination by E2 and E3 enzymes is a predominant mechanism regulating protein function. Some RING E3s, including anaphase-promoting complex/cyclosome (APC), catalyze polyubiquitination by sequential reactions with two different E2s. An initiating E2 ligates ubiquitin to an E3-bound substrate. Another E2 grows a polyubiquitin chain on the ubiquitin-primed substrate through poorly defined mechanisms. Here we show that human APC's RING domain is repurposed for dual functions in polyubiquitination. The canonical RING surface activates an initiating E2-ubiquitin intermediate for substrate modification. However, APC engages and activates its specialized ubiquitin chain-elongating E2 UBE2S in ways that differ from current paradigms. During chain assembly, a distinct APC11 RING surface helps deliver a substrate-linked ubiquitin to accept another ubiquitin from UBE2S. Our data define mechanisms of APC/UBE2S-mediated polyubiquitination, reveal diverse functions of RING E3s and E2s, and provide a framework for understanding distinctive RING E3 features specifying ubiquitin chain elongation.