A Glutathione Transferase from Agrobacterium tumefaciens Reveals a Novel Class of Bacterial GST SuperfamilyReport as inadecuate




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In the present work, we report a novel class of glutathione transferases GSTs originated from the pathogenic soil bacterium Agrobacterium tumefaciens C58, with structural and catalytic properties not observed previously in prokaryotic and eukaryotic GST isoenzymes. A GST-like sequence from A. tumefaciens C58 Atu3701 with low similarity to other characterized GST family of enzymes was identified. Phylogenetic analysis showed that it belongs to a distinct GST class not previously described and restricted only in soil bacteria, called the Eta class H. This enzyme designated as AtuGSTH1-1 was cloned and expressed in E. coli and its structural and catalytic properties were investigated. Functional analysis showed that AtuGSTH1-1 exhibits significant transferase activity against the common substrates aryl halides, as well as very high peroxidase activity towards organic hydroperoxides. The crystal structure of AtuGSTH1-1 was determined at 1.4 Å resolution in complex with S-p-nitrobenzyl-glutathione Nb-GSH. Although AtuGSTH1-1 adopts the canonical GST fold, sequence and structural characteristics distinct from previously characterized GSTs were identified. The absence of the classic catalytic essential residues Tyr, Ser, Cys distinguishes AtuGSTH1-1 from all other cytosolic GSTs of known structure and function. Site-directed mutagenesis showed that instead of the classic catalytic residues, an Arg residue Arg34, an electron-sharing network, and a bridge of a network of water molecules may form the basis of the catalytic mechanism. Comparative sequence analysis, structural information, and site-directed mutagenesis in combination with kinetic analysis showed that Phe22, Ser25, and Arg187 are additional important residues for the enzyme-s catalytic efficiency and specificity.



Author: Katholiki Skopelitou, Prathusha Dhavala, Anastassios C. Papageorgiou, Nikolaos E. Labrou

Source: http://plos.srce.hr/



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