Lebetase, an alpha(beta)-fibrin(ogen)olytic metalloproteinase of Vipera lebetina snake venom, is inhibited by human alpha-macroglobulins.

The effects of the plasma proteinase inhibitors alpha(2)-macroglobulin (alpha(2)M) and the alpha(2)M-related pregnancy zone protein (PZP) were evaluated towards the metalloproteinase lebetase, isolated from Vipera lebetina venom. We demonstrate that lebetase interacts with both inhibitors. Cleavage of alpha(2)M by lebetase resulted in the formation of 90-kDa fragments, and covalent complexes of alpha(2)M with lebetase were observed. The proteolytic activity of lebetase against fibrinogen and azocasein could be inhibited by alpha(2)M. Cleavage of PZP also resulted in the formation of 90-kDa fragments, and complexes of both dimer and tetramer forms of PZP with lebetase were detected. The amino acid sequence identification of the sites of specific proteolysis of alpha(2)M and PZP demonstrate that the cleavage sites are within the bait regions of both proteins. Lebetase I cleaves between Arg(696)-Leu(697), which is one of the most common cleavage sites in alpha(2)M by proteinases. The other two cleavage sites in alpha(2)M by lebetase are Gly(679)-Leu(680) and His(694)-Ala(695). The cleavage between Pro(689)-Gln(690) is the only cleavage site identified in PZP. In that lebetase is an anticoagulation agent in vivo, we propose that the interaction of lebetase with alpha(2)M may suggest a reduced fibrin(ogen)olytic activity of lebetase in human.