Effect of Vibrio-Derived Extracellular Protease vEP-45 on the Blood Complement System

SIMPLE SUMMARY: An extracellular Vibrio protease called vEP-45 can activate the complement system through an alternative pathway by cleaving key complement precursors, including C3 and C5, to their active forms, which can induce innate immunity. ABSTRACT: Vibrio vulnificus is a pathogenic bacterium that can causes wound infections and fetal septicemia. We have reported that V. vulnificus ATCC29307 produces an extracellular zinc-metalloprotease (named vEP-45). Our previous results showed that vEP-45 can convert prothrombin to active thrombin and also activate the plasma kallikrein/kinin system. In this study, the effect of vEP-45 on the activation of the complement system was examined. We found that vEP-45 could proteolytically convert the key complement precursor molecules, including C3, C4, and C5, to their corresponding active forms (e.g., C3a, C3b, C4a, C4b, and C5a) in vitro cleavage assays. C5b production from C5 cleavage mediated by vEP-45 was not observed, whereas the level of C5a was increased in a dose-dependent manner compared to that of the non-treated control. The cleavage of the complement proteins in human plasma by vEP-45 was also confirmed via Western blotting. Furthermore, vEP-45 could convert C3 and C5 to active C3a and C5a as a proinflammatory mediator, while no cleavage of C4 was observed. These results suggest that vEP-45 can activate the complement system involved in innate immunity through an alternative pathway.