title: The lipid binding site of the phosphatidylcholine transfer protein from bovine liver.
abstract: The phosphatidylcholine transfer protein (PC-TP) from bovine liver has a binding site for phosphatidylcholine (PC). Structural and molecular characteristics of this site were investigated by binding PC-analogues carrying photolabile, fluorescent and short-chain fatty acids. Analysis of the photolabeled PC/PC-TP adduct showed that the hydrophobic peptide segment Val171-Phe-Met-Tyr-Tyr-Phe-Asp177 is part of the lipid binding site for the 2-acyl chain. This site was further studied by binding PC carrying cis-parinaric acid at the sn-2-position. Time resolved fluorescence anisotropy measurements indicated that the 2-acyl chain was immobilized following the rotation of PC-TP. Similar experiments with PC carrying cis-parinaric acid at the sn-1-position demonstrated that the 1-acyl chain was immobilized as well but at a site distinctly different from that of the 2-acyl chain. Binding sites for the 1- and 2-acyl chain were then explored by use of PC-isomers carrying decanoic, lauric and myristic acid at the sn-1- (or sn-2-)-position and oleic acid at the sn-2- (or sn-1-)-position. Incubation with vesicles prepared of these PC-species indicated that binding to PC-TP diminished with decreasing acyl chain length but more so for species with short-chain fatty acids on the sn-2-position than on the sn-1-position. Transfer experiments confirmed that PC-TP discriminates between PC-isomers of apparently equal hydrophobicity favouring the transfer of these species carrying oleic acid at the sn-2-position.
mesh_terms: D000727:Androgen-Binding Protein; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D005227:Fatty Acids / Q000032:analysis; D005454:Fluorescence Polarization; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008954:Models, Biological; D010446:Peptide Fragments / Q000032:analysis; D010713:Phosphatidylcholines / Q000378:metabolism*; D049294:Phospholipid Transfer Proteins; D011485:Protein Binding; D013329:Structure-Activity Relationship
chemical_list: D000727:Androgen-Binding Protein; D002352:Carrier Proteins; D005227:Fatty Acids; D010446:Peptide Fragments; D010713:Phosphatidylcholines; D049294:Phospholipid Transfer Proteins