title: Binding of GAPR-1 to negatively charged phospholipid membranes: unusual binding characteristics to phosphatidylinositol.
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 strongly associates with lipid rafts at the cytosolic leaflet of the Golgi membrane. The myristoyl moiety at the N-terminus of GAPR-1 contributes to membrane binding but is not sufficient for stable membrane anchorage. GAPR-1 is positively charged at physiological pH, which allows for additional membrane interactions with proteins or lipids. To determine the potential contribution of lipids to membrane binding of GAPR-1, we used a liposome binding assay. Here we report that non-myristoylated GAPR-1 stably binds liposomes that contain the negatively charged lipids phosphatidylserine, phosphatidylglycerol, phosphatidylinositol, or phosphatidic acid. GAPR-1 displays the highest preference for phosphatidic acid-containing liposomes. In contrast, lysozyme, which contains a similar surface charge, did not bind to these liposomes, except for a weak membrane association with PA-containing liposomes. Interestingly, GAPR-1 binds to phosphatidylinositol with unusual characteristics. Denaturation or organic extraction of GAPR-1 does not result in dissociation of phosphatidylinositol from GAPR-1. The association of phosphatidylinositol with GAPR-1 results in a diffuse gel-shift in SDS-PAGE. Mass spectrometric analysis of gel-shifted GAPR-1 showed the association of up to 3 molecules of phosphatidylinositol with GAPR-1. These results suggest that the lipid composition contributes to the GAPR-1 binding to biological membranes.
authors.affiliation: Department of Biochemistry and Cell Biology and Institute of Biomembranes, Utrecht University, Utrecht.
authors.forename: Josse
authors.initials: J
authors.lastname: Van Galen
authors.forename: Bas W M
authors.initials: BW
authors.lastname: Van Balkom
authors.forename: Ramon L
authors.initials: RL
authors.lastname: Serrano
authors.forename: Dora
authors.initials: D
authors.lastname: Kaloyanova
authors.forename: Ruud
authors.initials: R
authors.lastname: Eerland
authors.forename: Ernstpeter
authors.initials: E
authors.lastname: Stüven
authors.forename: J Bernd
authors.initials: JB
authors.lastname: Helms
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism*; D011485:Protein Binding; D013696:Temperature; D013997:Time Factors
chemical_list: D008565:Membrane Proteins; D010716:Phosphatidylinositols