Ligand determinants of nisin for its induction activity.

Nisin has been widely used in the food industry as a safe and natural preservative and has the potential to be used as a biomedicine. Improving nisin production is important for its enormous applications. Nisin A is produced in Lactococcus lactis and its biosynthesis is induced through the regulation of the 2-component system NisKR. In this study, alanine-scanning mutagenesis was applied to study the key structure or AA in nisin for inducing the 2-component system NisKR to regulate downstream gene expression. Assay of β-galactosidase activity revealed that either ring A or ring B was necessary for nisin to induce lacZ reporter gene expression. A substituted first ring formed by Thr2 and Cys7 in S3A instead of ring A (formed by Ser3 and Cys7) fully retained nisin induction activity. Mutation of cationic AA and addition of cationic ions hardly affected nisin induction activity. These results demonstrated that the N-terminal ring structures in nisin were involved in activating NisKR to act as an inducing molecule, whereas the electrostatic force might not contribute to this process. In addition, 2 specific residues were revealed to have potential for improving both nisin induction and antimicrobial activity, which might be used for increasing nisin production.