1.Site directed mutagenesis of Schizosaccharomyces pombe glutathione synthetase produces an enzyme with homoglutathione synthetase activity.
Dworeck T1, Zimmermann M. PLoS One. 2012;7(10):e46580. doi: 10.1371/journal.pone.0046580. Epub 2012 Oct 16.
Three different His-tagged, mutant forms of the fission yeast glutathione synthetase (GSH2) were derived by site-directed mutagenesis. The mutant and wild-type enzymes were expressed in E. coli DH5α and affinity purified in a two-step procedure. Analysis of enzyme activity showed that it was possible to shift the substrate specificity of GSH2 from Gly (k(m) 0,19; wild-type) to β-Ala or Ser. One mutation (substitution of Ile471, Cy472 to Met and Val and Ala 485 and Thr486 to Leu and Pro) increased the affinity of GSH2 for β-Ala (k(m) 0,07) and lowered the affinity for Gly (k(m) 0,83), which is a characteristic of the enzyme homoglutathione synthetase found in plants. Substitution of Ala485 and Thr486 to Leu and Pro only, increased instead the affinity of GSH2 for Ser (k(m) 0,23) as a substrate, while affinity to Gly was preserved (k(m) 0,12). This provides a new biosynthetic pathway for hydroxymethyl glutathione, which is known to be synthesized from glutathione and Ser in a reaction catalysed by carboxypeptidase Y.
2.The distribution of glutathione and homoglutathione in leaf, root and seed tissue of 73 species across the three sub-families of the Leguminosae.
Colville L1, Sáez CM2, Lewis GP3, Kranner I4. Phytochemistry. 2015 Jul;115:175-83. doi: 10.1016/j.phytochem.2015.01.011. Epub 2015 Feb 6.
Homoglutathione (γ-glutamyl-cysteinyl-β-alanine) is a homologue of glutathione (γ-glutamyl-cysteinyl-glycine), which is a ubiquitous and indispensable tripeptide in eukaryotes with multi-facetted functions, many of which relate to cellular redox regulation. Homoglutathione is unique to the Leguminosae family, but studies of its occurrence have been restricted to the Papilionoideae subfamily, and almost exclusively to crop species. To determine whether the distribution of homoglutathione in the Leguminosae has a phylogenetic basis the occurrence of homoglutathione was investigated in the leaves, roots and seeds of 73 wild species of Leguminosae, representing 30 tribes across the Caesalpinioideae, Mimosoideae and Papilionoideae subfamilies. Homoglutathione was found only in the Papilionoideae, and was generally restricted to the 'Old World Clade'. It is proposed that homoglutathione may have arisen following a whole genome duplication event after the divergence of the Old World Clade.
3.The thiol compounds glutathione and homoglutathione differentially affect cell development in alfalfa (Medicago sativa L.).
Pasternak T1, Asard H2, Potters G3, Jansen MA4. Plant Physiol Biochem. 2014 Jan;74:16-23. doi: 10.1016/j.plaphy.2013.10.028. Epub 2013 Nov 5.
Glutathione (GSH) is an important scavenger of Reactive Oxygen Species (ROS), precursor of metal chelating phytochelatins, xenobiotic defence compound and regulator of cell proliferation. Homoglutathione (hGSH) is a GSH homologue that is present in several taxa in the family of Fabaceae. It is thought that hGSH performs many of the stress-defence roles typically ascribed to GSH, yet little is known about the potential involvement of hGSH in controlling cell proliferation. Here we show that hGSH/GSH ratios vary across organs and cells and that these changes in hGSH/GSH ratio occur during dedifferentiation and/or cell cycle activation events. The use of a GSH/hGSH biosynthesis inhibitor resulted in impaired cytokinesis in isolated protoplasts, showing the critical importance of these thiol-compounds for cell division. However, exposure of isolated protoplasts to exogenous GSH accelerated cytokinesis, while exogenous hGSH was found to inhibit the same process.
