Post-translational modification of nisin. The involvement of NisB in the dehydration process

The lantibiotic nisin is an antimicrobial peptide produced by Lactococcus lactis. As with all lantibiotics, nisin contains a number of dehydro-residues and thioether amino acids that introduce five lanthionine rings into the target peptide. These atypical amino acids are introduced by post-translational modification of a ribosomally synthesized precursor peptide. In certain cases, the serine residue, at position 33 of nisin, does not undergo dehydration to Dha33. With native nisin this partially processed form represents about 10% of the total peptide, whereas with the engineered variants, [Trp30]nisin A and [Lys27,Lys31]nisin A, the proportion of peptide that escapes full processing was found to be to approximately 50%. This feature of nisin biosynthesis was exploited in an investigation of the role of the NisB protein in pre-nisin maturation. Manipulation of the level of NisB was achieved by cloning and overexpressing the plasmid-encoded nisB gene in a range of different nisin-producing strains. The resulting fourfold increase in the level of NisB significantly increased the efficiency of the dehydration reaction at Ser33. The final secreted product of biosynthesis by these strains was the homogenous form of the fully processed nisin (or nisin variant) molecule. The results presented represent the first experimental evidence for the direct involvement of the NisB protein in the maturation process of nisin.