PMP1 18-38, a yeast plasma membrane protein fragment, binds phosphatidylserine from bilayer mixtures with phosphatidylcholine: A H-2-NMR study

PMP1 is a 38-residue plasma membrane protein of the yeast Saccharomyces cer evisiae that regulates the activity of the H+-ATPase. The cytoplasmic domai n conformation results in a specific interfacial distribution of five basic side chains, thought to strongly interact with anionic phospholipids. We h ave used the PMP1 18-38 fragment to carry out a deuterium nuclear magnetic resonance (H-2-NMR) study for investigating the interactions between the PM P1 cytoplasmic domain and phosphatidylserines. For this purpose, mixed bila yers of 1-palmitoyl, 2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palm itoyl, 2-oleoyl-sn-glycero-3-phosphoserine (POPS) were used as model membra nes (POPC/POPS 5:1, m/m). Spectra of headgroup- and chain-deuterated POPC a nd POPS phospholipids, POPC-d4, POPC-d31, POPS-d3, and POPS-d31, were recor ded at different temperatures and for various concentrations of the PMP1 fr agment. Data obtained from POPS deuterons revealed the formation of specifi c peptide-POPS complexes giving rise to a slow exchange between free and bo und PS lipids, scarcely observed in solid-state NMR studies of lipid-peptid e/protein interactions. The stoichiometry of the complex (8 POPS per peptid e) was determined and its significance is discussed. The data obtained with headgroup-deuterated POPC were rationalized with a model that integrates t he electrostatic perturbation induced by the cationic peptide on the negati vely charged membrane interface, and a "spacer" effect due to the intercala tion of POPS/PMP1f complexes between choline headgroups.