Vitronectin and its fragments purified as serum inhibitors of Staphylococcus aureus γ‐hemolysin and leukocidin, and their specific binding to the Hlg2 and the LukS components of the toxins

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Abstract
Staphylococcal γ‐hemolysin and leukocidin are bi‐component cytolysins, consisting of LukF (or Hlg1)/Hlg2 and LukF/LukS, respectively. Here, we purified serum inhibitors of γ‐hemolysin and leukocidin from human plasma. Protein sequencing showed that the purified inhibitors of 62, 57, 50 and 38 kDa were the vitronectin fragments with truncation(s) of the C‐terminal or both N‐ and C‐terminal regions. The purified vitronectin fragments specifically bound to the Hlg2 component of γ‐hemolysin and the LukS component of leukocidin to form high‐molecular‐weight complexes with them, leading to inhibition of the toxin‐induced lysis of human erythrocytes and human polymorphonuclear leukocytes, respectively. Intact vitronectin also showed inhibitory activity to the toxins. The ability of γ‐hemolysin and leukocidin to bind vitronectin and its fragments is a novel function of the pore‐forming cytolysins.