title: Interaction of GAPR-1 with lipid bilayers is regulated by alternative homodimerization.
abstract: Golgi-Associated Plant Pathogenesis-Related protein 1 (GAPR-1) is a mammalian protein that belongs to the superfamily of plant pathogenesis related proteins group 1 (PR-1). GAPR-1 is a peripheral membrane-binding protein that strongly associates with lipid-enriched microdomains at the cytosolic leaflet of Golgi membranes. Little is known about the mechanism of GAPR-1 interaction with membranes. We previously suggested that dimerization plays a role in the function of GAPR-1 and here we report that phytic acid (inositol hexakisphosphate) induces dimerization of GAPR-1 in solution. Elucidation of the crystal structure of GAPR-1 in the presence of phytic acid revealed that the GAPR-1 dimer differs from the previously published GAPR-1 dimer structure. In this structure, one of the monomeric subunits of the crystallographic dimer is rotated by 28.5°. To study the GAPR-1 dimerization properties, we investigated the interaction with liposomes in a light scattering assay and by flow cytometry. In the presence of negatively charged lipids, GAPR-1 caused a rapid and stable tethering of liposomes. [D81K]GAPR-1, a mutant predicted to stabilize the IP6-induced dimer conformation, also caused tethering of liposomes. [A68K]GAPR-1 however, a mutant predicted to stabilize the non-rotated dimer conformation, is capable of binding to liposomes but did not cause liposome tethering. Our combined data suggest that the charge properties of the lipid bilayer can regulate GAPR-1 dynamics as a potential mechanism to modulate GAPR-1 function.
authors.affiliation: Department of Biochemistry and Cell Biology, Utrecht University, Utrecht, The Netherlands.
authors.forename: Josse
authors.initials: J
authors.lastname: van Galen
authors.forename: Nick K
authors.initials: NK
authors.lastname: Olrichs
authors.forename: Arie
authors.initials: A
authors.lastname: Schouten
authors.forename: Ramon L
authors.initials: RL
authors.lastname: Serrano
authors.forename: Esther N M
authors.initials: EN
authors.lastname: Nolte-'t Hoen
authors.forename: Ruud
authors.initials: R
authors.lastname: Eerland
authors.forename: Dora
authors.initials: D
authors.lastname: Kaloyanova
authors.forename: Piet
authors.initials: P
authors.lastname: Gros
authors.forename: J Bernd
authors.initials: JB
authors.lastname: Helms
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D002850:Chromatography, Gel; D018360:Crystallography, X-Ray / Q000379:methods; D019281:Dimerization; D005434:Flow Cytometry / Q000379:methods; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry*; D008954:Models, Biological; D008958:Models, Molecular; D008968:Molecular Conformation; D009154:Mutation; D010716:Phosphatidylinositols / Q000737:chemistry; D010833:Phytic Acid / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011487:Protein Conformation
chemical_list: C458481:GLIPR2 protein, human; D008051:Lipid Bilayers; D008055:Lipids; D008081:Liposomes; D008565:Membrane Proteins; D010716:Phosphatidylinositols; D010833:Phytic Acid