Mechanism of ubiquitin ligation and lysine prioritization by a HECT E3.

ABSTRACT: Ubiquitination by HECT E3 enzymes regulates myriad processes, including tumor suppression, transcription, protein trafficking, and degradation. HECT E3s use a two-step mechanism to ligate ubiquitin to target proteins. The first step is guided by interactions between the catalytic HECT domain and the E2?ubiquitin intermediate, which promote formation of a transient, thioester-bonded HECT?ubiquitin intermediate. Here we report that the second step of ligation is mediated by a distinct catalytic architecture established by both the HECT E3 and its covalently linked ubiquitin. The structure of a chemically trapped proxy for an E3?ubiquitin-substrate intermediate reveals three-way interactions between ubiquitin and the bilobal HECT domain orienting the E3?ubiquitin thioester bond for ligation, and restricting the location of the substrate-binding domain to prioritize target lysines for ubiquitination. The data allow visualization of an E2-to-E3-to-substrate ubiquitin transfer cascade, and show how HECT-specific ubiquitin interactions driving multiple reactions are repurposed by a major E3 conformational change to promote ligation. DOI:http://dx.doi.org/10.7554/eLife.00828.001.

SUBMITTER: Kamadurai HB 

PROVIDER: S-EPMC3738095 | biostudies-literature | 2013 Aug

REPOSITORIES: biostudies-literature