cDNA cloning and deduced amino acid sequence of fibrinolytic enzyme (lebetase) from Vipera lebetina snake venom

Abstract

The complete amino acid sequence of lebetase is deduced from the nucleotide sequence of a cDNA clone isolated by screening a venomous gland c DNA library of Central Asian Vipera lebetina snake. The cDNA sequence with 2011 basepairs encodes an open reading frame of 478 amino acids which includes an 18 amino acid signal peptide, plus an 175 amino acid segment of zymogen-like propeptide, a mature protein of 204 amino acids, a spacer of 18 amino acids and a disintegrin-like peptide of 63 amino acids. The mature protein lebetase as isolated from the crude venom has the molecular weight of approximately 23.7 kD and, thus, lebetase as well as several other snake venom metalloproteinases is translated as a precursor protein, which may be processed posttranslationally. The lebetase proprotein has a "cysteine switch" motif (PKMCGV) similar to that involved in the activation of matrix metalloproteinase zymogens. The mature protein (residues 223-427) shows the strongest similarity with fibrolase (63% identity), fibrinolytic enzyme from Agkistrodon contortrix contortrix venom. The metalloproteinase domain has a typical zinc-chelating sequence (HEXXHXXGXXH). In the disintegrin-like domain of protein, the RGD sequence is replaced by VGD.