title: Asymmetric coiled-coil structure with Guanine nucleotide exchange activity.
abstract: Vesicular traffic during exocytosis is regulated by Rab GTPase, Sec4p in yeast, which is activated by a guanine nucleotide exchange factor (GEF) called Sec2p. The GEF activity is localized in the N-terminal 160 residues of Sec2p, which lacks sequence similarity with any other GEFs with known structures, and thereby the guanine nucleotide exchange mechanism by Sec2p remains unknown. Here, we report the crystal structure of the Sec2p GEF domain at 3.0 A resolution. The structure unexpectedly consists of a homodimeric, parallel coiled coil that extends over 180 A. Pull-down and guanine nucleotide exchange analyses on a series of deletion and point mutants of Sec2p unveiled the catalytic residues for its GEF activity as well as the Sec4p binding site, thus presenting a nucleotide exchange mechanism by a simple coiled coil. The present functional analyses allow us to build the Sec2p:Sec4p complex model, which explains the specificity for Rab GTPases by their respective GEF proteins.
authors.affiliation: Department of Biological Information, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Yokohama-shi, Kanagawa, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Sato
authors.forename: Ryutaro
authors.initials: R
authors.lastname: Shirakawa
authors.forename: Hisanori
authors.initials: H
authors.lastname: Horiuchi
authors.forename: Naoshi
authors.initials: N
authors.lastname: Dohmae
authors.forename: Shuya
authors.initials: S
authors.lastname: Fukai
authors.forename: Osamu
authors.initials: O
authors.lastname: Nureki
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003461:Crystallography; D019281:Dimerization; D019204:GTP-Binding Proteins / Q000737:chemistry*; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry*; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry*; D020691:rab GTP-Binding Proteins / Q000737:chemistry*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; C064456:SEC2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D019204:GTP-Binding Proteins; C064320:SEC4 protein, S cerevisiae; D020691:rab GTP-Binding Proteins