The crystal structures of CsGST in two different space groups revealed that Asp26 and His79 coordinate a zinc ion. In one space group, His46 of an adjacent molecule participates in the coordination within 2.0 angstrom. In the other space group, Asp26, His79 and a water molecule coordinate a zinc ion. The CsGST-D26H structure showed that four histidine residues - His26 and H1s79 from one molecule and the same residues from a symmetry-related neighboring molecule - coordinate a zinc ion. The coordinated zinc ions are located between two molecules and mediate molecular contacts within the crystal. (C) 2013 Elsevier Inc. All rights reserved.