title: Structure of an E3:E2~Ub complex reveals an allosteric mechanism shared among RING/U-box ligases.
abstract: Despite the widespread importance of RING/U-box E3 ubiquitin ligases in ubiquitin (Ub) signaling, the mechanism by which this class of enzymes facilitates Ub transfer remains enigmatic. Here, we present a structural model for a RING/U-box E3:E2~Ub complex poised for Ub transfer. The model and additional analyses reveal that E3 binding biases dynamic E2~Ub ensembles toward closed conformations with enhanced reactivity for substrate lysines. We identify a key hydrogen bond between a highly conserved E3 side chain and an E2 backbone carbonyl, observed in all structures of active RING/U-Box E3/E2 pairs, as the linchpin for allosteric activation of E2~Ub. The conformational biasing mechanism is generalizable across diverse E2s and RING/U-box E3s, but is not shared by HECT-type E3s. The results provide a structural model for a RING/U-box E3:E2~Ub ligase complex and identify the long sought-after source of allostery for RING/U-Box activation of E2~Ub conjugates.
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Pruneda
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Littlefield
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Soss
authors.forename: Kyle A
authors.initials: KA
authors.lastname: Nordquist
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Chazin
authors.forename: Peter S
authors.initials: PS
authors.lastname: Brzovic
authors.forename: Rachel E
authors.initials: RE
authors.lastname: Klevit
mesh_terms: D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D011485:Protein Binding; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction; D025801:Ubiquitin / Q000737:chemistry / Q000378:metabolism*; D044763:Ubiquitin-Conjugating Enzymes / Q000737:chemistry* / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D021122:Protein Subunits; D025801:Ubiquitin; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases