Purification and characterization of thaumatopain, a cysteine protease from the arils of the plant Thaumatococcus daniellii

Abstract

Aqueous extracts of the aril of the seed of Thaumatococcus daniellii contain, in addition to the intensely sweet protein thaumatin, a cysteine protease that we have termed thaumatopain. Thaumatopain has been purified by ion-exchange chromatography from arils, and is a monomeric protein of Mr 30,000. The protease strongly resembles papain in proteolytic activity, pH optima, susceptibility to inhibitors of cysteine proteases and in N-terminal sequence. The protease has also been identified in crude aril extracts by affinity labelling with iodo[14C]acetate. Thaumatopain is responsible for the cysteine protease activity previously attributed to thaumatin. Thaumatin is digested by thaumatopain at neutral to alkaline pH values.