Complete Amino Acid Sequence of the Lentil Trypsin−Chymotrypsin Inhibitor LCI-1.7 and a Discussion of Atypical Binding Sites of Bowman−Birk Inhibitors

The complete primary structure of the lentil (Lens culinaris) trypsin−chymotrypsin inhibitor LCI-1.7 was determined by conventional methods in order to find relationships between partial sequences and the difference in action against human and bovine chymotrypsin. As other Bowman−Birk type inhibitors, LCI-1.7 contained 68 amino acid residues, seven disulfide bridges, and two reactive sites, Arg16−Ser17 for trypsin and Tyr42−Ser43 for chymotrypsin. Evaluation of sequence homologies showed that it belonged to the group III Bowman−Birk inhibitors. The atypical additional binding site of LCI-1.7 for human chymotrypsin was discussed and compared with such binding sites of two other Bowman−Birk inhibitors, the Bowman−Birk soybean proteinase inhibitor BBI, and the lima bean proteinase inhibitor LBI I, for human and bovine trypsin and chymotrypsin. A concept to reduce the action of these inhibitors against human enzymes by genetic engineering was proposed. Keywords: Amino acid sequence; atypical binding sites; Bowman−Birk inhibitor; chymotrypsin inhibitor; disulfide bridges; Glycine max; inhibition of bovine proteinases; inhibition of human proteinases; Lens culinaris; lentil; lima bean; Phaseolus lunatus; primary structure; reactive sites; soybean; trypsin inhibitor