title: A catalytic coiled coil: structural insights into the activation of the Rab GTPase Sec4p by Sec2p.
abstract: Rab GTPases, the largest subgroup in the superfamily of Ras-like GTPases, play regulatory roles in multiple steps of intracellular vesicle trafficking. They are activated by guanine nucleotide exchange factors (GEFs), which catalyze the interconversion of the GDP-bound, or inactive, form of Rab to the GTP-bound, or active, form. Relatively little is known of the mechanisms by which GEFs activate Rabs. Here, we present the crystal structure of the GEF domain of Sec2p in complex with its Rab partner Sec4p. The Sec2p GEF domain is a 220 Angstroms long coiled coil, striking in its simplicity and in the use of the coiled-coil motif for catalysis. The structure suggests a mechanism whereby Sec2p induces extensive structural rearrangements in the Sec4p switch regions and phosphate-binding loop that are incompatible with nucleotide binding. We show that Sec2p is specific for Sec4p and that specificity determinants reside in the two switch regions of Sec4p.
authors.affiliation: Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA.
authors.forename: Gang
authors.initials: G
authors.lastname: Dong
authors.forename: Martina
authors.initials: M
authors.lastname: Medkova
authors.forename: Peter
authors.initials: P
authors.lastname: Novick
authors.forename: Karin M
authors.initials: KM
authors.lastname: Reinisch
mesh_terms: D020816:Amino Acid Motifs; D001665:Binding Sites; D001692:Biological Transport; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D020662:Guanine Nucleotide Exchange Factors; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009711:Nucleotides / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D016415:Sequence Alignment; D022161:Transport Vesicles / Q000502:physiology; D020691:rab GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D009711:Nucleotides; C064456:SEC2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D019204:GTP-Binding Proteins; C064320:SEC4 protein, S cerevisiae; D020691:rab GTP-Binding Proteins