Inhibitory effect of α2-macroglobulin on vibrio vulnificus protease

Vibrio vulnificus, an etiologic agent of wound infections and septicemia in humans, elaborates a metalloprotease which is known to be an important virulence factor of the Vibrio. The proteolytic activity of V. vulnificus metalloprotease (VVP) toward casein and elastin was inhibited by α2-macroglobulin (α2 M) at the molar ratio of 1: 1, although partial activity was maintained. Permeability-enhancing and hemorrhagic activities were also inhibited, but the peptidase activity toward Z-Gly-Phe-NH2 was not reduced, even by an excess amount of α2 M. VVP formed a complex with α2 M through cleavage of the bait regions of all four α2 M subunits and elicitation of conformational change of the α2 M molecule, which resulted in entrapment of VVP in the α2 M molecule. The peptidase activity of α2 M-WP complex was inhibited by low-molecular-weight inhibitors such as phosphoramidon, but IgG antibody against VVP failed to neutralize its peptidase activity. Of human plasma proteins, a2 M was the only inhibitor for WP. These findings indicate that VVP produced during V. vulnificus infection is inactivated by plasma α2 M that leaks from the vascular system.