Adipocytefatty acid binding prothln (AFABP) binds nkiativfly charghd phospholipid mkmbranhs through electrostatic interactions

AI;ABP is thought to transfer unesterified fatty acids (FA) tu phospholipid membranes lia a collisionai mechanism which involves ionic interactions between lysine residues nn the protein surface and phospholipid headgroups hi tins studl. lve demonstrated that AFABP can electrostatically hind to amodie phospholipid membranes AFABP caused small uni lame liar lchicles ( Sl ' V > containing either cardiolipin or phosphatidic acid to aggregate and precipitate by low-speed ( 14,000g) centrifugation. with the ratio of phospholipid to AI- ABP in the precipitate equalling 24; l. No precipitation occurred when AFABP u .is mixed with J.witterionic SUV, nor when acctvlatcd AFABP. in which surface llsmes had been chemically neutralized, was mixed with anionic membranes AFABP binding to acidic membranes depended upon the ionic strength of ihe reaction buffer: >200 mM NaCI reduced protem-lipid complex formation m parallel lvith a decrease m I-A transfer rate. AI;ABP, but not acctl lated Af-ABI', prevented cvioclirorne c. a well-characterized peripheral membrane protein, from binding to membranes. In addition. AFABP displaced membrane-bound cjiochromc c. FinaN>, SL'V caused a marked shift in circular dichioic spectra o| AFABP. further supporting the hypothesis that AFABP binds to membranes. 'Ihus. although generally described as a cytosolic protein. AFABP may interact with membranes to help target I-'A to miracellular sites of miliiation.