Glutathione S-transferases (GSTs) are multifunctional enzymes that are used as fusion tags on recombinant proteins in mammalian and Escherichia coil expression systems. We recently found that the Schistosoma japonicum GST (SjGST) displays weak Ni2+ ion binding affinity. Glu26 and His79 were assumed to be its Ni2+ binding sites based on the structure of the 26-kDa Clonorchis sinensis GST. To enhance SjGST Ni2+ binding affinity, Glu26 was mutated to His. SjGST-E26H was expressed and purified at a high concentration of imidazole to a higher purity than wild type SjGST. In addition, human biotin protein ligase fused to SjGST-E26H was purified with a immobilized Ni affinity column. (C) 2010 Elsevier Inc. All rights reserved.