title: The Sec7 N-terminal regulatory domains facilitate membrane-proximal activation of the Arf1 GTPase.
abstract: The Golgi complex is the central sorting compartment of eukaryotic cells. Arf guanine nucleotide exchange factors (Arf-GEFs) regulate virtually all traffic through the Golgi by activating Arf GTPase trafficking pathways. The Golgi Arf-GEFs contain multiple autoregulatory domains, but the precise mechanisms underlying their function remain largely undefined. We report a crystal structure revealing that the N-terminal DCB and HUS regulatory domains of the Arf-GEF Sec7 form a single structural unit. We demonstrate that the established role of the N-terminal region in dimerization is not conserved; instead, a C-terminal autoinhibitory domain is responsible for dimerization of Sec7. We find that the DCB/HUS domain amplifies the ability of Sec7 to activate Arf1 on the membrane surface by facilitating membrane insertion of the Arf1 amphipathic helix. This enhancing function of the Sec7 N-terminal domains is consistent with the high rate of Arf1-dependent trafficking to the plasma membrane necessary for maximal cell growth.
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States.|Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, United States.
authors.forename: Brian C
authors.identifier: http://orcid.org/0000-0002-5434-1500
authors.initials: BC
authors.lastname: Richardson
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States.|Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, United States.
authors.forename: Steve L
authors.initials: SL
authors.lastname: Halaby
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States.|Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, United States.
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Gustafson
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States.|Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, United States.
authors.forename: J Christopher
authors.identifier: http://orcid.org/0000-0002-8837-0473
authors.initials: JC
authors.lastname: Fromme
mesh_terms: D020823:ADP-Ribosylation Factor 1 / Q000378:metabolism*; D018360:Crystallography, X-Ray; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D012441:Saccharomyces cerevisiae / Q000201:enzymology*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; C066755:Sec7 guanine nucleotide exchange factors; D020823:ADP-Ribosylation Factor 1
keywords: <i>s. cerevisiae</i>; GTPase; Golgi; T. terrestris; biophysics; cell biology; structural biology; vesicle traffic