title: ArfGAP1 responds to membrane curvature through the folding of a lipid packing sensor motif.
abstract: ArfGAP1 promotes GTP hydrolysis in Arf1, a small G protein that interacts with lipid membranes and drives the assembly of the COPI coat in a GTP-dependent manner. The activity of ArfGAP1 increases with membrane curvature, suggesting a negative feedback loop in which COPI-induced membrane deformation determines the timing and location of GTP hydrolysis within a coated bud. Here we show that a central sequence of about 40 amino acids in ArfGAP1 acts as a lipid-packing sensor. This ALPS motif (ArfGAP1 Lipid Packing Sensor) is also found in the yeast homologue Gcs1p and is necessary for coupling ArfGAP1 activity with membrane curvature. The ALPS motif binds avidly to small liposomes and shows the same hypersensitivity on liposome radius as full-length ArfGAP1. Site-directed mutagenesis, limited proteolysis and circular dichroism experiments suggest that the ALPS motif, which is unstructured in solution, inserts bulky hydrophobic residues between loosely packed lipids and forms an amphipathic helix on highly curved membranes. This helix differs from classical amphipathic helices by the abundance of serine and threonine residues on its polar face.
authors.affiliation: CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Sophia Antipolis, France.
authors.forename: Joëlle
authors.initials: J
authors.lastname: Bigay
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Casella
authors.forename: Guillaume
authors.initials: G
authors.lastname: Drin
authors.forename: Bruno
authors.initials: B
authors.lastname: Mesmin
authors.forename: Bruno
authors.initials: B
authors.lastname: Antonny
mesh_terms: D020727:ADP-Ribosylation Factors / Q000737:chemistry*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000737:chemistry; D002942:Circular Dichroism; D004268:DNA-Binding Proteins / Q000737:chemistry; D020690:GTPase-Activating Proteins / Q000737:chemistry*; D006868:Hydrolysis; D057927:Hydrophobic and Hydrophilic Interactions; D008081:Liposomes / Q000737:chemistry; D008563:Membrane Lipids / Q000737:chemistry*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D017510:Protein Folding; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry
chemical_list: C503239:Arfgap1 protein, rat; D004268:DNA-Binding Proteins; C089147:GCS1 protein, S cerevisiae; D020690:GTPase-Activating Proteins; D008081:Liposomes; D008563:Membrane Lipids; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D020727:ADP-Ribosylation Factors