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

The lantibiotic nisin is an antimicrobial peptide produced by Lactococcus l actis. As with all lantibiotics, nisin contains a number of dehydro-residue s and thioether amino acids that introduce five lanthionine rings into the target peptide. These atypical amino acids are introduced by post-translati onal modification of a ribosomally synthesized precursor peptide. In certai n cases, the serine residue, at position 33 of nisin, does not undergo dehy dration to Dha33. With native nisin this partially processed form represent s about 10% of the total peptide, whereas with the engineered variants, [Tr p30]nisin A and [Lys27,Lys31]nisin A, the proportion of peptide that escape s full processing was found to be to approximately 50%. This feature of nis in biosynthesis was exploited in an investigation of the role of the NisB p rotein in pre-nisin maturation. Manipulation of the level of NisB was achie ved by cloning and overexpressing the plasmid-encoded nisB gene in a range of different nisin-producing strains. The resulting fourfold increase in th e level of NisB significantly increased the efficiency of the dehydration r eaction at Ser33. The final secreted product of biosynthesis by these strai ns was the homogenous form of the fully processed nisin (or nisin variant) molecule. The results presented represent the first experimental evidence f or the direct involvement of the NisB protein in the maturation process of nisin.