Fig. 2
From: Insights into APC/C: from cellular function to diseases and therapeutics
Mechanisms of Ubiquitin chain formation by the APC/C. The APC/C catalytic polyubiquitination chain formation by two-step sequential reactions with two E2s: initiating E2 (E2i) and elongating E2 (E2e). In homo sapiens, the “initiating” E2s, UBCH5 or UBCH10, with APC/C complex ligates ubiquitin to substrate and the “elongating” E2 UBE2S expands a K11 polyubiquitination chain on the Ubiquitin-primed substrate. The UBCH5 or UBCH10 binds to APC11 to initiate substrate ubiquitinated, then the UBE2S is recruited to the APC/C by Cdh1/Cdc20. In the chain elongating assembly, the APC/C binding site and the non-canonical distinct APC11 RING surface helps UBE2S deliver K11 polyubiquitination chain to the substrate. In S. cerevisiae, the “initiating” E2, Ubc4 and the “elongating” E2 Ubc1 deliver a K48 polyubiquitination chain to the substrate