Polymorphism of trypsin and chymotrypsin binding loops in Bowman-Birk inhibitors from common bean (Phaseolus vulgaris L.)

The Bowman-Birk inhibitors (BBI) are found widespread in legume species. The primary structure of 23 BBI sequences, isolated from genomic DNA of eight Italian landraces of common bean (Phaseolus vulgaris L.), is presented in this study. The similarity among the analysed sequences ranged from 92 to 99%. The sequences, though highly similar to those previously described for common bean, showed some distinct features. Differences were detected in number of cysteine residues and in both trypsin and chymotrypsin binding loops. Two variants of trypsin binding loop, differing for the residue at P_2 position (Ile or Arg) and two variants of chymotrypsin binding loop showing at the P1 position Leu or Phe were found. Although P_2 -Ile is the most frequent residue observed in natural BBI sequences as well as in this study, the detection of the variant P_2 -Arg in four landraces make them very interesting for further investigations. In fact, sources of different BBI are very interesting due to the different inhibitory activity associated to them.