A Positively Selected Residue Influences Enzyme Functionalities

Glutathione transferases (GSTs) are a family of multifunctional enzymes that utilize the tripeptide glutathione (GSH) to detoxify a wide range of electrophiles. The GSTs are grouped into different classes based on protein sequecne similarities, but although members of a class have high sequcence identities they often display different substrate specificities. In the Mu GSTs there is evidence that a limited number of positively selected residues drive the evolution towards novel enzyme functions1. Residue 210 is one of these residues. In the present study we show by saturation‐mutagenesis of residue 210 in human GST M2‐2 how point mutations can differentially change the the enzyme’s substrate‐activity profile with alternative substrates. This demonstrates how the residue may have played a role as a functional switch in the evolution of the Mu class genes, since a duplicated gene can quite easily recruit a novel function,. Crystal structures clarify that removal of steric hindrance of a methyl group enables activity with epoxides, while other activites are maintained in the variant enzymes. The work in the authors’ laboratory was supported by the Swedish Research Council. Y.I. and M. A. were recipients of stipends from the Sven and Lilly Lawski Foundation.