title: Ube2W conjugates ubiquitin to α-amino groups of protein N-termini.
abstract: The covalent attachment of the protein ubiquitin to intracellular proteins by a process known as ubiquitylation regulates almost all major cellular systems, predominantly by regulating protein turnover. Ubiquitylation requires the co-ordinated action of three enzymes termed E1, E2 and E3, and typically results in the formation of an isopeptide bond between the C-terminal carboxy group of ubiquitin and the ϵ-amino group of a target lysine residue. However, ubiquitin is also known to conjugate to the thiol of cysteine residue side chains and the α-amino group of protein N-termini, although the enzymes responsible for discrimination between different chemical groups have not been defined. In the present study, we show that Ube2W (Ubc16) is an E2 ubiquitin-conjugating enzyme with specific protein N-terminal mono-ubiquitylation activity. Ube2W conjugates ubiquitin not only to its own N-terminus, but also to that of the small ubiquitin-like modifier SUMO (small ubiquitin-related modifier) in a manner dependent on the SUMO-targeted ubiquitin ligase RNF4 (RING finger protein 4). Furthermore, N-terminal mono-ubiquitylation of SUMO-2 primes it for poly-ubiquitylation by the Ubc13-UEV1 (ubiquitin-conjugating enzyme E2 variant 1) heterodimer, showing that N-terminal ubiquitylation regulates protein fate. The description in the present study is the first of an E2-conjugating enzyme with N-terminal ubiquitylation activity, and highlights the importance of E2 enzymes in the ultimate outcome of E3-mediated ubiquitylation.
authors.affiliation: Wellcome Trust Centre for Gene Regulation and Expression, Sir James Black Centre, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Tatham
authors.forename: Anna
authors.initials: A
authors.lastname: Plechanovová
authors.forename: Ellis G
authors.initials: EG
authors.lastname: Jaffray
authors.forename: Helena
authors.initials: H
authors.lastname: Salmen
authors.forename: Ronald T
authors.initials: RT
authors.lastname: Hay
mesh_terms: D009687:Nuclear Proteins / Q000378:metabolism; D025841:Small Ubiquitin-Related Modifier Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism*; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination
chemical_list: D009687:Nuclear Proteins; C114070:RNF4 protein, human; C117909:SUMO2 protein, human; D025841:Small Ubiquitin-Related Modifier Proteins; D014157:Transcription Factors; D025801:Ubiquitin; C510626:UBE2W protein, human; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases
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