title: Solution structure of Vps27 UIM-ubiquitin complex important for endosomal sorting and receptor downregulation.
abstract: Monoubiquitylation is a well-characterized signal for the internalization and sorting of integral membrane proteins to distinct cellular organelles. Recognition and transmission of monoubiquitin signals is mediated by a variety of ubiquitin-binding motifs such as UIM, UBA, UEV, VHS and CUE in endocytic proteins. The yeast Vps27 protein requires two UIMs for efficient interactions with ubiquitin and for sorting cargo into multivesicular bodies. Here we show that the individual UIMs of Vps27 exist as autonomously folded alpha-helices that bind ubiquitin independently, non-cooperatively and with modest affinity. The Vps27 N-terminal UIM engages the Leu8-Ile44-Val70 hydrophobic patch of ubiquitin through a helical surface conserved in UIMs of diverse proteins, including that of the S5a proteasomal regulatory subunit. The Leu8-Ile44-Val70 ubiquitin surface is also the site of interaction for CUE and UBA domains in endocytic proteins, consistent with the view that ubiquitin-binding endocytic proteins act serially on the same monoubiquitylated cargo during transport from cell surface to the lysosome.
authors.affiliation: Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, IL 60208-3500, USA.
authors.forename: Kurt A
authors.initials: KA
authors.lastname: Swanson
authors.forename: Richard S
authors.initials: RS
authors.lastname: Kang
authors.forename: Svetoslava D
authors.initials: SD
authors.lastname: Stamenova
authors.forename: Linda
authors.initials: L
authors.lastname: Hicke
authors.forename: Ishwar
authors.initials: I
authors.lastname: Radhakrishnan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D056827:Endosomal Sorting Complexes Required for Transport; D006801:Humans; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D012441:Saccharomyces cerevisiae / Q000378:metabolism / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D025801:Ubiquitin / Q000378:metabolism*; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D010446:Peptide Fragments; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; C119627:VPS27 protein, S cerevisiae; D033921:Vesicular Transport Proteins