Comparative analysis of two stress-inducible tau class glutathione transferases from Glycine max revealed significant catalytic and structural diversification.

BACKGROUND

Glutathione transferases (GSTs, EC. 2.5.1.18) form a large group of multifunctional enzymes that are involved in the metabolism and inactivation of a wide range of endogenous and xenobiotic compound as well as in cell regulation and response to several biotic and abiotic stresses.

OBJECTIVE

In the present work, we report the comparative analysis of the structural and functional features of two isoenzymes (GmGSTU5-5 and GmGSTU8-8) of the glutathione transferase (GST) family from Glycine max.

METHODS

Full-length cDNA clones of GmGSTU5-5 and GmGSTU8-8 were derived from RT-PCR of RNA isolated from soybean seedlings and were cloned into a T7 expression vector. Τhe recombinant enzymes were expressed in E. coli and purified by affinity chromatography. Substrate specificity, kinetic and inhibition analysis were carried out towards a range of different xenobiotic compounds and GSH analogues. The thermal stability of the enzymes was also evaluated using activity assays and differential scanning fluorimetry.

RESULTS

Analysis of substrate specificity using a range of thiol substrates and electrophilic compounds suggested that both isoenzymes display broad and overlapping specificities. They are capable of detoxifying major stress-induced toxic products. Study of their ligandin-binding properties by kinetic analysis and molecular modelling indicated that both GmGSTU5-5 and GmGSTU8-8 bind a range of secondary metabolites and plant hormones, suggesting a role in transport or storage of bioactive compounds. Thermostability analysis showed that GmGSTU5-5 and GmGSTU8-8 display extraordinary thermal stability, compared to other plant GSTs.

CONCLUSIONS

Our results suggest that GmGSTU5-5 and GmGSTU8-8 display different or overlapping substrate specificities and kinetic properties. The biological role of GmGSTU5-5 and GmGSTU8-8 may be relevant to the detoxification of toxic compounds or the binding of bioactive metabolites that function in cell regulation and stress defence mechanisms.