A SINGLE-RESIDUE DELETION ALTERS THE LIPID SELECTIVITY OF A K-ASSOCIATED PEPTIDE IN THE BETA-CONFORMATION - SPIN-LABEL ELECTRON-SPIN-RESONANCE STUDIES( CHANNEL)

Lipid-peptide interactions with the 27-residue peptide of sequence KLE ALYILMVLGFFGFFTLGIMLSYIR reconstituted as beta-sheet assemblies in dim yristoylphosphatidylcholine bilayers have been studied by electron spi n resonance (ESR) spectroscopy with spin-labeled lipids. The peptide c orresponds to residues 42-68 of the IsK voltage-gated K+ channel prote in and contains the single putative transmembrane span of this protein . Lipid-peptide interactions give rise to a second component in the ES R spectra of lipids spin-labeled on the 14C atom of the chain that cor responds to restriction of the lipid mobility by direct interaction wi th the peptide assemblies. From the dependence on the lipid/peptide ra tio, the stoichiometry of lipid interaction is found to be about two p hospholipids/peptide monomer. The sequence of selectivity for lipid as sociation with the peptide assemblies is in the order phosphatidic aci d > stearic acid = phosphatidylserine > phosphatidylglycerol = phospha tidylcholine. Comparison with previous data for a corresponding 26-res idue mutant peptide with a single deletion of the apolar residue Leu(2 ) (Horvath et al., 1995, Biochemistry 34:3893-3898), indicates a very similar mode of membrane incorporation for native and mutant peptides, but a strongly modified pattern and degree of specificity for the int eraction with negatively charged lipids. The latter is interpreted in terms of the relative orientations of the charged amino acid side chai ns in the beta-sheet assemblies of the native and deletion-mutant pept ides.