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

Abstract

The effects of the plasma proteinase inhibitors α 2-macroglobulin (α 2M) and the α 2M-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 α 2M by lebetase resulted in the formation of 90-kDa fragments, and covalent complexes of α 2M with lebetase were observed. The proteolytic activity of lebetase against fibrinogen and azocasein could be inhibited by α 2M. 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 α 2M 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 α 2M by proteinases. The other two cleavage sites in α 2M 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 α 2M may suggest a reduced fibrin(ogen)olytic activity of lebetase in human.