title: Structure of guanine-nucleotide-exchange factor human Mss4 and identification of its Rab-interacting surface.
abstract: Guanine-nucleotide-exchange factors (GEFs) promote the exchange of GDP for GTP in Ras GTPases, and thereby positively regulate their functions. Members of the Sec4/Ypt1/Rab branch of the Ras superfamily are essential for vesicular transport. A GEF for a subset of Rab proteins, termed mammalian suppressor of Sec4 (Mss4), has been identified. Here we use multidimensional NMR to determine the structure of human Mss4 (hMss4), which is the first tertiary structure established for a protein with GEF activity. Mss4 contains a central beta-sheet sandwiched between two small sheets. It also binds a Zn2+ ion through Cys 23, Cys 26, Cys 94 and Cys 97. The Rab-binding surface of hMss4 has subsequently been delineated using chemical-shift perturbation experiments and site-directed mutagenesis. The active site of hMss4 involves the Zn(2+)-binding region and a neighbouring loop.
authors.affiliation: Howard Hughes Medical Institute, Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: H
authors.initials: H
authors.lastname: Yu
authors.forename: S L
authors.initials: SL
authors.lastname: Schreiber
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D019204:GTP-Binding Proteins / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013499:Surface Properties; D015032:Zinc / Q000737:chemistry; D020692:rab3 GTP-Binding Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D011506:Proteins; C489794:RABIF protein, human; D020663:ras Guanine Nucleotide Exchange Factors; D019204:GTP-Binding Proteins; D020692:rab3 GTP-Binding Proteins; D018631:ras Proteins; D015032:Zinc