Purification of a novel pepsin inhibitor from Coriolus versicolor and its biochemical properties.

A novel pepsin inhibitor was isolated from Coriolus versicolor. The purification was carried out by a 2-step ultrafiltration followed by DEAE-52 and Mono Q ion-exchange chromatography. SDS-PAGE and gel filtration chromatography analysis showed that the isolated inhibitor was a 22.3 kDa protein with a single subunit. Heat stability of this inhibitor was estimated and only 7% of its inhibitory activity lost after treatment at 98 degrees C. The inhibitor was more specific against pepsin than several other proteases. The dissociation constant (Ki) and concentration required for 50% pepsin inhibition (IC50) were 5.84 x 10-5 M and 26.26 mu g/mL, respectively. Apparent decrease of a-helix and increase of random coil were observed in the circular dichroism spectra of pepsin when an equimolar amount of the inhibitor was added. The inhibition mechanism of this inhibitor differs from the reported aspartic protease inhibitors, according to the secondary structure and the kinetic studies of this inhibitor.