An NMR Study on the Phase Change of Lipid Membranes by an Antimicrobial Peptide, Protegrin-1

Membrane disruption by an antimicrobial peptide, protegrin-1 (PG-1), was investigated by measuring the (2)H solid-state nuclear magnetic resonance (SSNMR) spectra of 1-palmitoyl-d(31)-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC_d31) in the mixture of PG-1 and POPC_d(31) lipids deposited on thin cover-glass plates. The experimental line shapes of anisotropic (2)H SSNMR spectra measured at various peptide-to-lipid (P/L) ratios were simulated reasonably by assuming the mosaic spread of bilayers containing pore structures or the coexistence of the mosaic spread of bilayers and a fast-tumbling isotropic phase. Within a few days of incubation in the hydration chamber, the pores were formed by the peptide in the POPC_d(31) and POPC_d(31)/cholesterol membranes. However, the formation of the pores was not clear in the POPC_d(31)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG) membrane. Over a hundred days after hydration, a rapidly rotating isotropic phase increased in the POPC_d(31) and the POPC_d(31)/cholesterol membranes with the higher P/L ratios, but no isotropic phase appeared in the POPC_d(31)/POPG membrane. Cholesterol added in the POPC bilayer acted as a stabilizer of the pore structure and suppressed the formation of a fast-tumbling isotropic phase.