Improved purification and some properties of megacin Cx, a bacteriocin produced by Bacillus megaterium

Megacin Cx is a bacteriocidal protein, previously described by Durner and Mach (Durner, K. (1970) Z. Allg. Mikrobiol. 10, 93-102; Durner, K. (1970) Z. Allg. Mikrobiol. 10, 373-382; Durner, K., and Mach, F. (1966) Zentralbl. Bakteriol. Parasitenkd. Infektionskr. Hyg. Abt. I Orig. 2, 120, 565-575), which is released into the medium during growth by Bacillus megaterium strain 337. We have optimized the culturing conditions to achieve reproducibly high yields of this protein; under these conditions, megacin Cx represents about one-half of the protein secreted into the medium. We have developed improved methods of purifying the protein to homogeneity. The active form of megacin Cx is a monomeric protein, a single polypeptide of Mr = 210,000, as determined by analytical ultracentrifugation and gel electrophoresis in sodium dodecyl sulfate. Like many other proteins secreted by Gram-positive organisms, megacin Cx contains remarkably little methionine and cysteine. The purified protein blocks protein synthesis in sensitive cells, but has little immediate effect upon nucleic acid synthesis. Our purification procedure separates megacin Cx from another activity in the culture medium which blocks the synthesis of RNA and DNA, as well as synthesis of protein, in sensitive cells.