Structural variations in nisin associated with different membrane mimicking and pH environments

Nisin is a membrane active antimicrobial peptide containing unusual dehydrated amino acid residues. The secondary structure of nisin in aqueous solution, membrane mimicking solvents and at various pH values was investigated using circular dichroism. In aqueous solution nisin is largely randomly coiled. In liposomes and at pH 6 and above, however, the presence of a maximum at 195 nm and a minimum at 190 nm was notable and indicative of β-turn formation in these environments. This change in structure was speculated to result in an increasing unavailability of the site for initial reaction of peptide and membrane at higher pH.