Crystal structure of the N-terminal domain of anaphase-promoting complex subunit 7.

Anaphase-promoting complex or cyclosome (APC/C) is an unusual E3 ubiquitin ligase and an essential protein that controls mitotic progression. APC/C includes at least 13 subunits, but no structure has been determined for any tetratricopeptide repeat (TPR)-containing subunit (Apc3 and -6-8) in the TPR subcomplex of APC/C. Apc7 is a TPR-containing subunit that exists only in vertebrate APC/C. Here we report the crystal structure of quad mutant of nApc7 (N-terminal fragment, residues 1-147) of human Apc7 at a resolution of 2.5 A. The structure of nApc7 adopts a TPR-like motif and has a unique dimerization interface, although the protein does not contain the conserved TPR sequence. Based on the structure of nApc7, in addition to previous experimental findings, we proposed a putative homodimeric structure for full-length Apc7. This model suggests that TPR-containing subunits self-associate and bind to adaptors and substrates via an IR peptide in TPR-containing subunits of APC/C.