Cloning, expression and mutational studies of a trypsin inhibitor that retains activity even after cyanogen bromide digestion.

ABSTRACT

A winged bean trypsin inhibitor (WbTI-2) of molecular mass ∼20kDa, has been cloned and expressed in Escherichiacoli with full activity like the one from seed protein. It completely inhibits trypsin at an enzymeinhibitor molar ratio of 12. PCR with cDNA and genomic DNA using same primers produced about 550 base pair product, which indicated it to be an intronless gene. Through site-directed mutagenesis, the Arg64 has been confirmed as the P1 residue. For the presence of five methionine residues in WbTI-2, cyanogen bromide (CNBr) digestion was carried out. Out of three fragments the one (about 65% of original size) containing the reactive site loop retained 50% activity.