IMPROVEMENT OF SOLUBILITY AND STABILITY OF THE ANTIMICROBIAL PEPTIDE NISIN BY PROTEIN ENGINEERING

Nisin is a 3.4-kDa antimicrobial peptide that, as a result of posttran slational modifications, contains unsaturated amino acids and lanthion ine residues, It is applied as a preservative in various food products . The solubility and stability of nisin and nisin mutants have been st udied. It is demonstrated that nisin mutants can be produced with impr oved functional properties. The solubility of nisin A is highest at lo w pH values and gradually decreases by almost 2 orders of magnitude wh en the pH of the solution exceeds a value of 7, At low pH, nisin Z exh ibits a decreased solubility relative to that of nisin A; at neutral a nd higher pH values, the solubilities of both variants are comparable. Two mutants of nisin Z, which contain lysyl residues at positions 27 and 31, respectively, instead of Asn-27 and His-31, were produced with the aim of reaching higher solubility at neutral pH. Both mutants wer e purified to homogeneity, and their structures were confirmed by one- and two-dimensional H-1 nuclear magnetic resonance, Their antimicrobi al activities were found to be similar to that of nisin Z, whereas the ir solubilities at pH 7 increased by factors of 4 and 7, respectively, The chemical stability of nisin A was studied in the pH range of 2 to 8 and at 20, 37, and 75 degrees C, Optimal stability was observed at pH 3.0, Nisin Z showed a behavior similar to that of nisin A. A mutant containing dehydrobutyrine at position 5 instead of dehydroalanine ha d lower activity but was significantly more resistant to acid-catalyze d chemical degradation than wild-type nisin Z.