INFLUENCE OF CHARGE DIFFERENCES IN THE C-TERMINAL PART OF NISIN ON ANTIMICROBIAL ACTIVITY AND SIGNALING CAPACITY

Three mutants of the lantibiotic nisin Z, in which the Val32 residue w as replaced by a Glu, Lys or Trp residue, were produced and characteri zed for the purpose of establishing the role of charge differences in the C-terminal part of nisin on antimicrobial activity and signaling p roperties. H-1-NMR analyses showed that all three mutants harbor an un modified serine residue at position 33, instead of the usual dehydroal anine. Apparently, the nature of the residue preceding the serine to b e dehydrated, strongly affects the efficiency of modification. Cleavag e of [Glu32,Ser33]nisin Z by endoproteinase Glu-C yielded [Glu32]nisin Z(1-32)-peptide, which has a net charge difference of -2 relative to wild-type nisin Z. The activity of [Lys32,Ser33]nisin Z against Microc occus flavus was similar to that of wild-type nisin, while [Trp32,Ser3 3]nisin Z, [Glu32,Ser33]nisin Z and [Glu32]nisin Z(1-32)-peptide exhib ited 3-5-fold reduced activity, indicating that negative charges in th e C-terminal part of nisin Z are detrimental for activity. All variant s showed significant loss of activity against Streptococcus thermophil us. The potency of the nisin variants to act as signaling molecules fo r auto-induction of biosynthesis was significantly reduced. To obtain mutant production, extracellular addition of (mutant) nisin Z to the l actococcal expression strains was essential.