The Alternative Pathway of Glutathione Degradation Is Mediated by a Novel Protein Complex Involving Three New Genes in Saccharomyces cerevisiae

Abstract

Glutathione (GSH), l-g-glutamyl-l-cysteinyl-glycine, is the major low-molecular-weight thiol compound present in almost all eukaryotic cells. GSH degradation proceeds through the g-glutamyl cycle that is initiated, in all organisms, by the action of g-glutamyl transpeptidase. A novel pathway for the degradation of GSH that requires the participation of three previously uncharacterized genes is described in the yeast Saccharomyces cerevisiae. These genes have been named DUG1 (YFR044c), DUG2 (YBR281c), and DUG3 (YNL191w) (defective in utilization of glutathione). Although dipeptides and tripeptides with a normal peptide bond such as cys-gly or glu-cys-gly required the presence of only a functional DUG1 gene that encoded a protein belonging to the M20A metallohydrolase family, the presence of an unusual peptide bond such as in the dipeptide, g-glu-cys, or in GSH, required the participation of the DUG2 and DUG3 gene products as well. The DUG2 gene encodes a protein with a peptidase domain and a large WD40 repeat region, while the DUG3 gene encoded a protein with a glutamine amidotransferase domain. The Dug1p, Dug2p, and Dug3p proteins were found to form a degradosomal complex through Dug1p-Dug2p and Dug2p-Dug3p interactions. A model is proposed for the functioning of the Dug1p/Dug2p/Dug3p proteins as a specific GSH degradosomal complex.

Glutathione biosynthesis in the yeast pathogens Candida glabrata and Candida albicans: essential in C. glabrata, and essential for virulence in C. albicans

“…Glutathione utilization in S. cerevisiae has been shown to require transport through a high-affinity glutathione transporter (Hgt1p), followed by its degradation through the Dug complex pathway for glutathione degradation (involving Dug1p, Dug2p and Dug3p) Ganguli et al, 2007). Putative orthologues of the Dug complex proteins (Dug1p, Dug2p and Dug3p) can be identified in C. glabrata by in silico analysis.…”

“…Disruption of glutathione biosynthesis in the yeasts Schizosaccharomyces pombe and S. cerevisiae, carried out by knocking out the first enzyme of glutathione biosynthesis, c-glutamyl cysteine synthase (GSH1 or GCS1), leads to glutathione auxotrophy, in which the cells become dependent for growth on exogenous glutathione, the uptake of which is mediated by high-affinity glutathione transporters. Furthermore, in S. cerevisiae, the exogenous glutathione can also be utilized as a sulphur source, and this utilization depends on the presence of the glutathione transporter as well as on an alternative pathway of glutathione degradation that involves the 'Dug pathway complex', comprising the three proteins Dug1p, Dug2p and Dug3p (Ganguli et al, 2007).…”

Aγ-Glutamyl Transpeptidase-Independent Pathway of Glutathione Catabolism to Glutamate via 5-Oxoproline in Arabidopsis

“…The similarity between rates of GSH degradation and 5OP accumulation suggests that the majority of GSH is metabolized through 5OP and that the major portion of 5OP is derived from GSH. These results also suggest that mechanisms for GSH degradation that do not proceed through 5OP, such as the GSH hydrolase activity of GGT or the newly discovered DUG hydrolase system in yeast (Ganguli et al, 2007), are of limited importance in total GSH turnover in plants.…”

Cytosolic γ-Glutamyl Peptidases Process Glutathione Conjugates in the Biosynthesis of Glucosinolates and Camalexin in Arabidopsis

“…The first one is puuD from E. coli, which has been shown to catalyze the hydrolysis of g-glutamyl-gaminobutyrate in the utilization pathway of putrescine (Kurihara et al, 2005(Kurihara et al, , 2006. The second one is DUG3 from the yeast Saccharomyces cerevisiae, which has been linked to the hydrolysis of the g-Glu-Cys peptide bond of GSH in a previously unknown GSH degradation pathway (Ganguli et al, 2007), although proof of its direct catalysis is missing. The structural resemblance between Gln, GSH conjugates, g-glutamyl-g-aminobutyrate, and GSH, namely, the shared g-glutamyl moiety, provides an explanation for the unexpected activities of GGPs, puuD and DUG3, and suggest that only the g-glutamyl moiety is crucial for substrate recognition.…”