Study On The Function Of The 29^th Serine Of Nisin

Nisin, produced by some species of Lactococcus lactis or Streptococcus uberis, is a kind of cationic peptide and is classified as type-A lantibiotic. Nisin can effectively inhibit many gram-positive bacteria, including many food putrefying bacteria and pathogenic bacteria, and nisin is safe to human being for it can be degraded byα-chymotrypsin. Now nisin is widely used as native food preservative in many countries and areas. Nisin has some defects, for example, only at acid condition can reach the best stability and solubility, and nisin shows relative narrow antibacterial spectrum, these defects limit the use of nisin.For a long time, scientists try to improve the property and extent the usage of nisin through study and understand the relationship between structure and function of nisin. Their efforts mainly focus on the ring and hinger regions and reveal some rules. Recently, our lab discovered that nisin resistance protein (NSR) perform nisin resistence function through cutting nisin molecular before the 29^th serine. and the amino acid sequence analyse reveal that the 29^th serine is the only un-modified serine in mature nisin molecular, these results indicated that the 29^th serine may have impact on nisin function.To study the function of the 29^th serine of nisin, we mutanted nisZ: the structure gene of nisinZ, changing the 29^th serine to the rest of other 19 amino acids separately, after subcloned the mutant nisZ into plasmid pMG36e and transformed the recombinant plasmids into Lactococcus lactis NZ9800, we acquired 19 recombinant strains, which expressed nisin mutant, and we examined the properities of nisinZ mutants.Our results showed that: the S29D nisinZ and S29A nisinZ mutant of 19 nisinZ mutants displayed enhanced activity than that of wide type, and the rest nisinZ mutants had decreased activity; S29A nisinZ exhibited enlarged antibacterial spectrum, it inhibited gram-positive bacteria: Staphylococcus epidermdis 1.2429, whereas the wide type had no inhibition completely; S29D nisinZ and S29A nisinZ mutants showed remarkable improvement of stability to heat than that of wide type, especial at high pH condition.Our study showed that the 29^th serine has closed relation to the activity, stability and antibacterial spectrum of nisin, further explored the structure-function relationship of nisin, helped us to understand nisin deeply, and provided feasible proof for optimizing nisin. But there are many details not clear now and needs further research.