Production of horsegram (Dolichos biflorus) Bowman-Birk inhibitor by an intein mediated protein purification system.

The seeds of the legume horsegram (Dolichos biflorus), a protein rich pulse (bean), contain multiple forms
of Bowman-Birk inhibitors (protease inhibitors). The major inhibitor HGI-III contains seven interweaving
disulfides and is extremely stable to high temperatures. A soluble HGI-III (rHGI) with the native N-terminus
was produced using a pTWIN IMPACT™ purification system. Yield of rHGI was improved by introducing
a trypsin sepharose affinity chromatography step resulting in �670 fold purification. The biochemical
characteristics of rHGI point to its close similarity to seed HGI-III not only in its structure but also in its
inhibitory characteristics toward bovine trypsin and chymotrypsin. The expression and purification strategy
presented here promises to produce BBIs in their natural form for pharmacological and therapeutic
use.