Expression, crystallization and preliminary X-ray analysis of ligand-free human glutathione S-transferase M2-2

Human glutathione-S-transferase M2-2 (hGSTM2-2) was expressed in Escherichia coli and purified by GSH-affinity chromatography. The recombinant enzyme and the protein isolated from human tissue were indistinguishable based on physicochemical, enzymatic and immunological criteria. The catalytically active dimeric hGSTM2-2 was crystallized without GSH or other active-site ligands in two crystal forms. Diffraction from form A crystals extends to 2.5 A and is consistent with the space group P21 (a = 53.9, b = 81.5, c = 55.6 A, beta = 109.26 A) with two monomers in the asymmetric unit. Diffraction from form B crystals extends to 3 A and is consistent with a space group P212121 (a = 57.2, b = 80.7, c = 225.9 A) with two dimers in the asymmetric unit. This is the first report of ligand-free mu-class GST crystals, and a comparison with liganded complexes will provide insight into the structural consequences of substrate binding which are thought to be important for catalysis.