Ubiquitin in Motion: Structural Studies of the Ubiquitin-Conjugating EnzymeUbiquitin Conjugate

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• 作者：Jonathan N. Pruneda ; Kate E. Stoll ; Laura J. Bolton ; Peter S. Brzovic ; Rachel E. Klevit
• 刊名：Biochemistry
• 出版年：2011
• 出版时间：March 15, 2011
• 年：2011
• 卷：50
• 期：10
• 页码：1624-1633
• 全文大小：1175K
• 年卷期：v.50,no.10(March 15, 2011)
• ISSN：1520-4995

文摘

Ubiquitination of proteins provides a powerful and versatile post-translational signal in the eukaryotic cell. The formation of a thioester bond between ubiquitin (Ub) and the active site of a ubiquitin-conjugating enzyme (E2) is critical for the transfer of Ub to substrates. Assembly of a functional ubiquitin ligase (E3) complex poised for Ub transfer involves recognition and binding of an E2Ub conjugate. Therefore, full characterization of the structure and dynamics of E2Ub conjugates is required for further mechanistic understanding of Ub transfer reactions. Here we present characterization of the dynamic behavior of E2Ub conjugates of two human enzymes, UbcH5cUb and Ubc13Ub, in solution as determined by nuclear magnetic resonance and small-angle X-ray scattering. Within each conjugate, Ub retains great flexibility with respect to the E2, indicative of highly dynamic species that adopt manifold orientations. The population distribution of Ub conformations is dictated by the identity of the E2: the UbcH5cUb conjugate populates an array of extended conformations, and the population of Ubc13Ub conjugates favors a closed conformation in which the hydrophobic surface of Ub faces helix 2 of Ubc13. We propose that the varied conformations adopted by Ub represent available binding modes of the E2Ub species and thus provide insight into the diverse E2Ub protein interactome, particularly with regard to interaction with Ub ligases.