Dehalogenation of Dichlorobenzoates by Acidovorax sp. KKS102’s beta class Glutathione S-transferase and its Mutants

Abstract

Glutathione s-transferases (GSTs) are ubiquitous family of enzymes well known for their detoxification function. Several different classes of the enzyme exist with beta class being the one specific to bacteria. Recently, the enzymes were found to exhibit other functions, in particular dehalogenation of some organic compounds. This property could be extremely useful especially in the bioremediation of some organochlorine pollutants. A beta class GST from Acidovorax sp. KKS102 designated as KKS-BphK was previously cloned and characterized. In this research, molecular docking study was first employed to investigate the possibility of binding of the protein to dichlorobenzoates; byproducts of polychlorobiphenyl degradation. The wild type enzyme together with other mutants were expressed using E. coli BL21 (DE3) cells and purified. The dehalogenation function of the enzymes against dichlorobenzoate derivatives was also investigated through chloride ion detection assay. The results of the molecular docking study indicated the possibility of binding of KKS-BphK to these substrates. Both the wild type and the mutants showed dehalogenation function against the model substrate 1-chloro-2,4- dinitrobenzene (CDNB). Furthermore, the enzymes also showed dehalogenation function against 2,4-dichlorobenzoate derivatives. However, in testing the activity of the enzymes toward 2,5- dichlorobenoate and 2,6-dichlorobenzoate, only K107T and A180P mutants showed some activity while the wild type and C10F mutant showed zero activity. The research indicates the usefulness of beta class GST in the dehalogenation of dichlorobenzoates in addition to their known function of dehalogenating monochlorobenzoates.