STRUCTURAL VARIATIONS IN NISIN ASSOCIATED WITH DIFFERENT MEMBRANE MIMICKING AND PH ENVIRONMENTS

Nisin is a membrane active antimicrobial peptide containing unusual de hydrated amino acid residues. The secondary structure of nisin in aque ous solution, membrane mimicking solvents and at various pH values was investigated using circular dichroism. In aqueous solution nisin is l argely randomly coiled. In liposomes and at pH 6 and above, however, t he presence of a maximum at 195 nm and a minimum at 190 nm was notable and indicative of beta-turn formation in these environments. This cha nge in structure was speculated to result in an increasing unavailabil ity of the site for initial reaction of peptide and membrane at higher pH. (C) 1998 Academic Press.