Pseudomonas reinekei MT1 is capable of growing on 4- and 5-chlorosalicylate as the sole carbon source involving a pathway with trans-dienelactone hydrolase as the key enzyme. This enzyme transforms 4-chloromuconolactone to maleylacetate and thereby avoids the spontaneous formation of toxic protoanemonin. trans-Dienelactone hydrolase is a Zn2+-dependent hydrolase where activity can be modulated by the exchange of Zn2+ by Mn2+ in at least two of the three metal-binding sites. Site directed variants of conserved residues of the Q(101)XXXQ(105)XD(107)XXXH(111) motif and of H281 and E294 exhibit a two order of magnitude decrease in activity and a strong decrease in metal-binding capability. As none of the variants exhibited a change in secondary structure, the analyzed amino acid residues can be assumed to be involved in metal binding, forming a novel trinuclear metal-binding motif. (C) 2009 Elsevier Inc. All rights reserved.