N-15 and P-31 solid-state NMR investigations on the orientation of zervamicin II and alamethicin in phosphatidylcholine membranes

The topologies of zervamicin II and alamethicin, labeled with N-15 uniforml y, selectively, or specifically, have been investigated by oriented proton- decoupled 15N solid-state NMR spectroscopy. Whereas at lipid-to-peptide (L/ P) ratios of 50 (wt/wt) zervamicin II exhibits transmembrane alignments in 1,2-dicapryl (di-C10:0-PC) and 1,2-dilauroyl (di-C12:0-PC) phosphatidylchol ine bilayers, it adopts orientations predominantly parallel to the membrane surface when the lengths of the fatty acyl chains are extended. The orient ational order of zervamicin II increases with higher phospholipid concentra tions, and considerable line narrowing is obtained in di-C10:0-PC/zervamici n II membranes at UP ratios of 100 (wt/wt). In contrast to zervamicin, alam ethicin is transmembrane throughout most, if not all, of its length when re constituted into 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayers. The P-31 solid-state NMR spectra of all phospholipid/peptaibol samples inv estigated show a high degree of headgroup order, indicating that the peptid es do not distort the bilayer structure. The observed differences in peptid e orientation between zervamicin and alamethicin are discussed with referen ce to differences in their lengths, helical conformations, distribution of (hydroxy)proline residues, and hydrophobic moments. Possible implications f or peptaibol voltage-gating are also described.