Scalable purification of the lantibiotic nisin and isolation of chemical/enzymatic cleavage fragments suitable for semi‐synthesis

Herein, we describe a scalable purification of the lantibiotic nisin via an extraction/precipitation approach using a biphasic system, which can be carried out up to 40–80 gram scale. This approach results in an at least tenfold enrichment of commercially available preparations of nisin, which usually contain only 2.5% of the desired peptide, to allow further purification by preparative HPLC. As a follow‐up study, the enriched nisin sample was digested either by trypsin or chymotrypsin, or treated by CNBr, and these reactions were monitored by LC‐MS to identify and characterize the obtained fragments. Two previously unknown cleavage sites have been identified: Asn20–Met21 and Met21–Lys22 for trypsin and chymotrypsin, respectively. Furthermore, a novel and convenient enzymatic approach to isolate the native nisin C‐ring nisin fragment (13–20)] was uncovered. Finally, by means of preparative HPLC, nisin fragments (1–12), (1–20), (22–34), and (22–31) could be isolated and will be used in a semi‐synthesis approach to elucidate the role of each fragment in the mode of action of nisin as an antimicrobial peptide. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.