Structural insights into the mechanism and E2 specificity of the RBR E3 ubiquitin ligase HHARI.

ABSTRACT: RING-in-between-RING (RBR) ubiquitin (Ub) E3 ligases function with Ub E2s through a RING/HECT hybrid mechanism to conjugate Ub to target proteins. Here, we report the crystal structure of the RBR E3, HHARI, in complex with a UbcH7?~?Ub thioester mimetic which reveals the molecular basis for the specificity of this cognate E2/RBR E3 pair. The structure also reveals mechanistically important conformational changes in the RING1 and UBA-like domains of HHARI that accompany UbcH7?~?Ub binding and provides a molecular basis by which HHARI recruits E2?~?Ub in an 'open' conformation. In addition to optimally functioning with an E2 that solely performs transthiolation, our data suggests that HHARI prevents spurious discharge of Ub from E2 to lysine residues by: (1) harboring structural elements that block E2?~?Ub from adopting a 'closed' conformation and (2) participating in contacts to ubiquitin that promote an open E2?~?Ub conformation.HHARI is a RING-in-between-RING (RBR) ubiquitin (Ub) E3 ligase. Here the authors present the crystal structure of HHARI with the UbcH7?~?Ub thioester intermediate mimetic, which reveals that HHARI binds this E2?~?Ub in an open conformation and explains the specificity of this cognate RBR E3/E2 pair.

SUBMITTER: Yuan L 

PROVIDER: S-EPMC5548887 | biostudies-literature | 2017 Aug

REPOSITORIES: biostudies-literature