Deciphering the Role of Individual Acyl Chains in the Interaction Network between Phosphatidylserines and a Single-Spanning Membrane Protein

PMP1 is a small single-spanning membrane protein functioning as a regulatory subunit of the yeast plasma membrane H+-ATPase. This protein forms a unique helix and exhibits a positively charged cytoplasmic domain that is able to specifically segregate phosphatidylserines (PSs). A marked groove formed at the helix surface is thought to play a major role in the related lipid−protein interaction network. Mutational analysis and 1H NMR experiments were therefore performed on a synthetic PMP1 fragment using DPC-d 38 micelles as a membrane-like environment, in the presence of small amounts of POPS. A mutation designed for altering the helix groove was shown to disfavor the POPS binding specificity as much as that affecting the electrostatic interaction network. From POPS titration experiments monitored by a full set of one- and two-dimensional NOESY spectra, the association between the phospholipids and the PMP1 peptide has been followed. Our data reveal that the clustering of POPS molecules is promoted from a stabilized framework obtained by coupling the PMP1 helix groove to a POPS sn-2 chain. To our knowledge, the NOE-based titration plots displayed in this report constitute the first NMR data that directly distinguish the role of the sn-1 and sn-2 acyl chains in a lipid−protein interaction. The results are discussed while taking into account our accurate knowledge of the yeast plasma membrane composition and its ability to form functional lipid rafts.