Purification of three cytosolic glutathione S-transferases from adult Schistosoma mansoni

Abstract

The cytosolic fraction of adult Schistosoma mansoni contains glutathione S-transferase (EC 2.5.1.18) activity, determined with the prototype substrate 1-chloro-2,4-dinitrobenzene, that is 5- to 50-fold greater than that found in other metazoan parasites. A survey of several model substrates revealed that enzymes in male and female schistosomes have distinct but overlapping substrate specificities. Four forms of glutathione S-transferase were detected, three of which, SmGST-1, SmGST-2, and SmGST-3, were purified to apparent homogeneity by glutathione affinity chromatography and HPLC chromatofocusing. The purified enzymes displayed very similar catalytic and physicochemical properties. They could be distinguished by differences in activity with ethacrynic acid and trans-4-phenyl-3-buten-2-one, but not with aryl halide substrates. The isoelectric points of SmGST-1, SmGST-2, and SmGST-3 were estimated to be 7.2, 7.1, 6.9, respectively. A polyclonal antiserum to SmGST-3 cross-reacted with the other two forms, but not with other soluble schistosome proteins. Each of the purified enzymes displayed an apparent subunit molecular weight of 28,500 by polyacrylamide gel electrophoresis under denaturing conditions. Gel filtration chromatography yielded a molecular weight of 30,800 for the catalytically active form of the enzyme. Unlike all known glutathione S-transferases, the three enzyme forms purified from S. mansoni appear to be catalytically active monomeric proteins.