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 Å and is consistent with the space group P2₁ (a = 53.9, b = 81.5, c = 55.6 Å, β = 109.26 Å) with two monomers in the asymmetric unit. Diffraction from form B crystals extends to 3 Å and is consistent with a space group P2₁2₁2₁ (a = 57.2, b = 80.7, c = 225.9 Å) 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.