Biochemical characterization and molecular cloning of a plasminogen activator proteinase (LV-PA) from bushmaster snake venom

The protein (LV-PA) from bushmaster (Lachesis muta muta) venom is a serine proteinase which specifically activates the inactive proenzyme plasminogen. LV-PA is a single chain glycoprotein with an apparent molecular mass of 33 kDa that fell to 28 kDa after treatment with N-Glycosidase F (PNGase F). Approximately 93% of its protein sequence was determined by automated Edman degradation of various fragments derived from a digestion with trypsin. A cDNA library of L. m. muta was constructed to generate expressed sequence tags (ESTs) and the plasminogen activator precursor cDNA was sequenced. The complete amino acid sequence of the enzyme was deduced from the cDNA sequence. LV-PA is composed of 234 residues and contains a single asparagine-linked glycosylation site, Asn-X-Ser, bearing sugars that account for approximately 10% of the enzyme's total molecular mass of 33 kDa. The sequence of LV-PA is highly similar to the plasminogen activators (PAs) TSV-PA from Trimeresurus stejnegeri venom and Haly-PA from Agkistrodon halys. Furthermore, the mature protein sequence of LV-PA exhibits significant similarity with other viperidae venom serine proteinases which affect many steps of hemostasis, ranging from the blood coagulation cascade to platelet function. The Michaelis constant (Km) and the catalytic rate constant (kcat) of LV-PA on four chromogenic substrates were obtained from Lineweaver-Burk plots. In addition, we used an indirect enzyme-linked immunoabsorbent assay (ELISA) to explore the phylogenetic range of immunological cross-reactivity (using antibodies raised against LV-PA) with analogous serine proteinases from two viperidae venoms and mammals.