Expression and characterization of Flavikunin: A Kunitz-type serine protease inhibitor identified in the venom gland cDNA library of Bungarus flaviceps.

Trancriptomic analysis of the venom gland cDNA library of Bungarus flaviceps revealed Kunitz-type serine protease inhibitor as one of the major venom protein families with three groups A, B, C. One of the group B isoforms named Flavikunin, which lacked an extra cysteine residue involved in disulfide bond formation in -bungarotoxin, was synthesized, cloned, and overexpressed in Escherichia coli. To decipher the structure-function relationship, the P1 residue of Flavikunin, histidine, was mutated to alanine and arginine. Purified wild-type and mutant Flavikunins were screened against serine proteases-thrombin, factor Xa, trypsin, chymotrypsin, plasmin, and elastase. The wild-type and mutant Flavikunin (HR) inhibited plasmin with an IC (50) of 0.48 and 0.35 mu M, respectively. The in-silico study showed that P1 residue of wild-type and mutant (HR) Flavikunin interacted with S1 and S1 site of plasmin, respectively. Thus, histidine at the P1 position was found to be involved in plasmin inhibition with mild anticoagulant activity.