PESTICIN DISPLAYS MURAMIDASE ACTIVITY

Pesticin of Yersinia pestis is the only bacteriocin that converts sens itive cells to stable spheroplasts. The amino acid sequence of pestici n as derived from the nucleotide sequence shows no similarity to those of any of the bacteriocins. The unique properties of pesticin prompte d an investigation of its mode of action. Since the pesticin plasmid d oes not encode a lysis protein for release of pesticin into the cultur e medium, pesticin was isolated from cells and purified to electrophor etic homogeneity. Highly purified pesticin degraded murein and murein glycan strands lacking the peptide side chains to products that were s imilar to those obtained by lysozyme, as revealed by high-resolution h igh-pressure liquid chromatography. After reduction of the murein degr adation products with tritium-labeled sodium borohydride, acid hydroly sis, and separation of the products by thin-layer chromatography, radi olabeled muraminitol was identified. This indicates that pesticin is a muramidase, and not an N-acetyl-glucosaminidase, that converts cells into stable spheroplasts by slowly degrading murein.