Journal
BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH
Volume 1823, Issue 11, Pages 2046-2056Publisher
ELSEVIER
DOI: 10.1016/j.bbamcr.2012.04.003
Keywords
Ubiquitin; Lys48-linked diubiquitin; Polyubiquitin; Ubiquitin-associated domain; Lysine-48 linkage selectivity
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Funding
- National Institutes of Health [GM065334, GM095755]
- National Center for Research Resources at the National Institutes of Health [RR-15301]
- U.S. Department of Energy, Office of Basic Energy Sciences [DE-AC02-06CH11357]
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Ubiquitin (Ub) is a small protein highly conserved among eukaryotes and involved in practically all aspects of eukaryotic cell biology. Polymeric chains assembled from covalently-linked Ub monomers function as molecular signals in the regulation of a host of cellular processes. Our previous studies have shown that the predominant state of Lys48-linked di- and tetra-Ub chains at near-physiological conditions is a closed conformation, in which the Ub-Ub interface is formed by the hydrophobic surface residues of the adjacent Ub units. Because these very residues are involved in (poly)Ub interactions with the majority of Ub-binding proteins, their sequestration at the Ub-Ub interface renders the closed conformation of polyUb binding incompetent. Thus the existence of open conformation(s) and the interdomain motions opening and closing the Ub-Ub interface is critical for the recognition of Lys48-linked polyUb by its receptors. Knowledge of the conformational properties of a polyUb signal is essential for our understanding of its specific recognition by various Ub-receptors. Despite their functional importance, open states of Lys48-linked chains are poorly characterized. Here we report a crystal structure of the open state of Lys48-linked di-Ub. Moreover, using NMR, we examined interactions of the open state of this chain (at pH4.5) with a Lys48-linkage-selective receptor, the UBA2 domain of a shuttle protein hHR23a. Our results show that di-Ub binds UBA2 in the same mode and with comparable affinity as the closed state. Our data suggest a mechanism for polyUb signal recognition, whereby Ub-binding proteins select specific conformations out of the available ensemble of polyUb chain conformations. This article is part of a Special Issue entitled: Ubiquitin Drug Discovery and Diagnostics. (c) 2012 Elsevier B.V. All rights reserved.
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