title: Structure of the GTPase-binding domain of Sec5 and elucidation of its Ral binding site.
abstract: The exocyst complex is involved in the final stages of exocytosis, when vesicles are targeted to the plasma membrane and dock. The regulation of exocytosis is vital for a number of processes, for example, cell polarity, embryogenesis, and neuronal growth formation. Regulation of the exocyst complex in mammals was recently shown to be dependent upon binding of the small G protein, Ral, to Sec5, a central component of the exocyst. This interaction is thought to be necessary for anchoring the exocyst to secretory vesicles. We have determined the structure of the Ral-binding domain of Sec5 and shown that it adopts a fold that has not been observed in a G protein effector before. This fold belongs to the immunoglobulin superfamily in a subclass known as IPT domains. We have mapped the Ral binding site on this domain and found that it overlaps with protein-protein interaction sites on other IPT domains but that it is completely different from the G protein-geranyl-geranyl interaction face of the Ig-like domain of the Rho guanine nucleotide dissociation inhibitor. This mapping, along with available site-directed mutagenesis data, allows us to predict how Ral and Sec5 may interact.
authors.affiliation: Department of Biochemistry, University of Cambridge, 80, Tennis Court Road, Cambridge CB2 1GA, United Kingdom. mott@bio.cam.ac.uk
authors.forename: Helen R
authors.initials: HR
authors.lastname: Mott
authors.forename: Daniel
authors.initials: D
authors.lastname: Nietlispach
authors.forename: Louise J
authors.initials: LJ
authors.lastname: Hopkins
authors.forename: Gladys
authors.initials: G
authors.lastname: Mirey
authors.forename: Jacques H
authors.initials: JH
authors.lastname: Camonis
authors.forename: Darerca
authors.initials: D
authors.lastname: Owen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D004926:Escherichia coli; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000032:analysis* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D033921:Vesicular Transport Proteins; D020725:ral GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: C511409:Exoc2 protein, mouse; D008565:Membrane Proteins; D033921:Vesicular Transport Proteins; D020558:GTP Phosphohydrolases; D020725:ral GTP-Binding Proteins