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

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.