Molecular Properties of Lysostaphin, a Bacteriolytic Agent Specific for Staphylococcus aureus

Lysostaphin is a zinc-metalloenzyme which has a molecular weight of 25,000 when determined by sedimentation equilibrium in dilute aqueous salt solutions. Combination of the sedimentation coefficient, s 20, w = 2.32, and diffusion coefficient, D 20, w = 7.83, gave a native molecular weight of 25,800. Sedimentation equilibrium of the protein in 6 m guanidine hydrochloride, with and without 2-mercaptoethanol, gave molecular weights of 25,800 and 27,800, respectively. The molecular weight of the fully dissociated protein was also determined to be 24,500 by the technique of gel filtration in 6 m guanidine hydrochloride and 25,500 by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. In each case, only a single protein species was shown to be present. These data indicate that the lysostaphin molecule is a single polypeptide chain. The frictional coefficient ratio for lysostaphin of 1.39 is higher than values obtained for most globular proteins. The optical rotatory dispersion spectrum was also different from that invariably observed with globular proteins and revealed no evidence of helical structure in the molecule. The amino acid composition of lysostaphin was unusual in that half-cystine was found to be absent.