title: The alpha helix of ubiquitin interacts with yeast cyclin-dependent kinase subunit CKS1.
abstract: Ubiquitin serves as a molecular zipcode to direct and sort ubiquitinylated proteins into distinct biological pathways. Although novel modes of ubiquitin interaction have recently been characterized, conventional ubiquitin-binding domains (UBDs) recognize ubiquitin through a hydrophobic pocket centered around isoleucine 44 and lined by residues in beta sheets 3 and 4. In this study, we report a novel mode of interaction between ubiquitin and the cyclin-dependent kinase subunit of Saccharomyces cerevisiae, Cks1p, an adaptor protein involved in transcriptional regulation through recruitment of proteasomal subunits to gene promoters. Cks1p interacts specifically with monoubiquitin and tetraubiquitin with an affinity several orders of magnitude greater than that of other ubiquitin-binding domains and in an unconventional fashion, which differs from interactions documented so far between ubiquitin and conventional UBDs. The loop between helices alpha 1 and alpha 2, and to a minor extent the N-terminal alpha-helix of Cks1p, are involved in the interaction with the alpha-helix of ubiquitin, instead of its I44-centered hydrophobic pocket. Not only is this the first time the alpha-helix of ubiquitin is implicated in a protein/protein interaction, thereby shedding new light on the mechanisms of ubiquitin recognition, but also the first report of a direct physical interaction between ubiquitin and Cks1p, inferring a role for ubiquitin binding in the transcriptional function of Cks1p.
authors.affiliation: Department Dynamics of Assembly of Complex Systems, Centre de Recherches en Biochimie Macromoléculaire, CNRS FRE2593, 1919 Route de Mende, Montpellier 34293, France.
authors.forename: Denis
authors.initials: D
authors.lastname: Tempé
authors.forename: Muriel
authors.initials: M
authors.lastname: Brengues
authors.forename: Pauline
authors.initials: P
authors.lastname: Mayonove
authors.forename: Hayat
authors.initials: H
authors.lastname: Bensaad
authors.forename: Céline
authors.initials: C
authors.lastname: Lacrouts
authors.forename: May C
authors.initials: MC
authors.lastname: Morris
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D001665:Binding Sites; D018797:Cell Cycle Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism*; D016415:Sequence Alignment; D025801:Ubiquitin / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C081185:CKS1 protein, S cerevisiae; D018797:Cell Cycle Proteins; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin