SECONDARY STRUCTURE AND MEMBRANE INTERACTION OF PR-39, A PRO-RICH ANTIBACTERIAL PEPTIDE(ARG)

PR-39 is a 4719-Da peptide isolated from pig intestine and belonging t o the recently discovered family of Pro+Arg-rich antibacterial peptide s. PR-39 does not lyse Escherichia coli, instead the lethal action is probably linked to the termination of DNA and protein synthesis [Boman , H. G., Agerberth, B. & Boman, A. (1993) Infect. Immun. 61, 2978-2984 ]. Circular dichroism and Fourier-transform infrared spectroscopy have been used to investigate the secondary structure of PR-39 in the abse nce or presence of lipids. According to the circular dichroic data, th is structure is not altered upon incubation of PR-39 with negatively c harged vesicles, although the infrared spectra suggest that the hydrog en bond pattern is modified upon the peptide-lipid interaction. This i s detected by a shift in the maximum wavelength of absorption of PR-39 from 1636 cm(-1) in the absence of lipids to 1645 cm(-1) in the prese nce of lipids. We have further addressed the question of the possible mechanism of interaction of PR-39 with model membranes (liposomes and planar lipid bilayers) whose lipid compositions mimick that of the E. coli inner membrane. PR-39 induced a calcein release from large unilam ellar vesicles, which is dependent upon the peptide concentration and upon the presence of negatively charged lipid (glycerophosphoglycerol) in the membrane. The binding study of PR-39 to dioleoylglycerophospho glycerol vesicles suggests that nearly 100% of the added peptide is me mbrane-bound. Addition of PR-39 to a planar lipid bilayer induced a li near increase in the current but no channel formation was observed sin ce no discrete steps of conductance occurred.