Solid-State NMR Investigation of the Selective Disruption of Lipid Membranes by Protegrin-1

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Abstract
The interaction of a β-hairpin antimicrobial peptide, protegrin-1 (PG-1), with various lipid membranes is investigated by 31P, 2H, and 13C solid-state NMR. Mixed lipid bilayers containing anionic lipids and cholesterol are used to mimic the bacterial and mammalian cell membranes, respectively. 31P and 2H spectra of macroscopically oriented samples show that PG-1 induces the formation of an isotropic phase in anionic bilayers containing phosphatidylglycerol. Two-dimensional 31P exchange experiments indicate that these isotropic lipids are significantly separate from the residual oriented lamellar bilayers, ruling out toroidal pores as the cause for the isotropic signal. 1H spin diffusion experiments show that PG-1 is not exclusively bound to the isotropic phase but is also present in the residual oriented lamellar bilayers. This dynamic and morphological heterogeneity of the anionic membranes induced by PG-1 is supported by the fact that 13C T2 relaxation times measured under cross polarization and direct polarization conditions differ significantly. In contrast to the anionic membrane, the zwitterionic phosphatidylcholine (PC) membrane does not form an isotropic phase in the presence of PG-1 but shows significant orientational disorder. The addition of cholesterol to the PC bilayer significantly reduces this orientational disorder. The 13C T2 relaxation times of the PC lipids in the presence of both cholesterol and PG-1 suggest that the peptide may decrease the dynamic heterogeneity of the cholesterol-containing membrane. The observed selective interaction of PG-1 with different lipid membranes is consistent with its biological function and may be caused by its strong cationic and amphipathic structure.