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.

► The major Bowman Birk protease inhibitor of horsegram (HGI-III) was expressed in E .coli.
► The protein was soluble, did not require refolding and retained its native N-terminus.
► Including a trypsin-sepharose affinity step results in ∼670 fold purification.
► The biochemical and kinetic properties of expressed protein was similar to HGI-III.
► This production system can be exploited for pharmacological and therapeutic use.