Purification, cloning and characterization of a metalloproteinase from Naja atra venom.

The complement system is a very important part of the immune system. Many snake venoms possess activities that influence the complement. A new metalloproteinase (termed atrase B) with anticomplementary activity was purified from Naja atra venom. Atrase B is a single chain glycoprotein with a molecular mass of 49.4 kDa and an isoelectric point of 9.7. Its N-terminal sequence shows high homology to those of metalloproteinases from cobra venoms. The cDNA sequence reveals that atrase B is a PIII class metalloproteinase. Atrase B slowly cleaves the Aα chain of fibrinogen. It also exhibits edema-inducing activity, but has no hemorrhagic activity and proteolytic activity against fibrin, azocasein, and N-benzoyl-l-arginine ethyl ester. Interestingly, atrase B inhibits activation of the complement classical and alternative pathways in a dose- and time-dependent manner. Complement components factor B and C6 are major targets for atrase B to cleave. Atrase B is the first identified SVMP that cleaves complement components factor B, C6, C7, and C8.