title: Crystal structure of Sar1-GDP at 1.7 A resolution and the role of the NH2 terminus in ER export.
abstract: The Sar1 GTPase is an essential component of COPII vesicle coats involved in export of cargo from the ER. We report the 1.7-A structure of Sar1 and find that consistent with the sequence divergence of Sar1 from Arf family GTPases, Sar1 is structurally distinct. In particular, we show that the Sar1 NH2 terminus contains two regions: an NH2-terminal extension containing an evolutionary conserved hydrophobic motif that facilitates membrane recruitment and activation by the mammalian Sec12 guanine nucleotide exchange factor, and an alpha1' amphipathic helix that contributes to interaction with the Sec23/24 complex that is responsible for cargo selection during ER export. We propose that the hydrophobic Sar1 NH2-terminal activation/recruitment motif, in conjunction with the alpha1' helix, mediates the initial steps in COPII coat assembly for export from the ER.
authors.affiliation: Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92130, USA.
authors.forename: M
authors.initials: M
authors.lastname: Huang
authors.forename: J T
authors.initials: JT
authors.lastname: Weissman
authors.forename: S
authors.initials: S
authors.lastname: Beraud-Dufour
authors.forename: P
authors.initials: P
authors.lastname: Luan
authors.forename: C
authors.initials: C
authors.lastname: Wang
authors.forename: W
authors.initials: W
authors.lastname: Chen
authors.forename: M
authors.initials: M
authors.lastname: Aridor
authors.forename: I A
authors.initials: IA
authors.lastname: Wilson
authors.forename: W E
authors.initials: WE
authors.lastname: Balch
mesh_terms: D000818:Animals; D022181:COP-Coated Vesicles / Q000378:metabolism; D003461:Crystallography; D004268:DNA-Binding Proteins; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000737:chemistry* / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006868:Hydrolysis; D057927:Hydrophobic and Hydrophilic Interactions; D008322:Mammals; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D020559:Monomeric GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D033921:Vesicular Transport Proteins; D015003:Yeasts
chemical_list: D004268:DNA-Binding Proteins; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; C485591:Preb protein, mouse; D011506:Proteins; C118289:SEC24 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D033921:Vesicular Transport Proteins; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D020559:Monomeric GTP-Binding Proteins; C077395:SAR1 protein, S cerevisiae