Assembly of k11-linked ubiquitin chains by the anaphase-promoting complex.

Ubiquitin chains are assembled, when a ubiquitin is connected to one of the seven Lys residues or the amino-terminus of a ubiquitin molecule already attached to a substrate. K48-linked ubiquitin chains target proteins for degradation by the 26S proteasome, while those chains connected through K63 regulate intracellular signaling cascades independently of protein degradation. Although all other linkages are detected in cells, their function is not well understood. Here, we review recent progress in delineating substrates, enzymes and functions of K11-linked ubiquitin chains. In particular, we discuss the mechanism of assembly for K11-linked chains by the human anaphase-promoting complex and its physiological E2s UbcH10 and Ube2S and we speculate on the particularities of these noncanonical chains in cells.