The glutathione-mediated detoxification pathway in yeast: an analysis using the red pigment that accumulates in certain adenine biosynthetic mutants of yeasts reveals the involvement of novel genes

Abstract

The glutathione-mediated pathway for the detoxification of endogenously and exogenously derived toxic compounds was investigated using a pigment that accumulates in certain adenine biosynthetic mutants of yeasts. The ade1 / ade2 mutants of Saccharomyces cerevisiae, when grown on adenine-limiting medium, accumulate a characteristic red pigment (ade pigment) in their vacuoles. The precursors of the ade pigments are toxic intermediates that form conjugates with glutathione, followed by their transport inside the vacuole. In this study, this red pigment was used as a phenotypic screen to obtain insight regarding new genes involved in the three phases of this detoxification pathway: the activation phase (phase I), the conjugation phase (phase II), and the efflux phase (phase III). Components of the phase III (efflux) pathway which includes, in addition to the previously characterized Ycf1p and Bpt1p, another member of the 'Ycf1p family', Bat1p, as well as a vacuolar H(+)-ATPase-dependent transport were identified. In the investigation of phase II (conjugation), it was found that glutathione S-transferases, encoded by GTT1 and GTT2,do not appear to play a role in this process. By contrast, two other previously characterized genes, the oxidative stress transcription factor gene, SKN7, and the yeast caesin protein kinase gene, YCK1, of S. cerevisiae do participate in this pathway.

ABC Transporters in Saccharomyces cerevisiae and Their Interactors: New Technology Advances the Biology of the ABCC (MRP) Subfamily

“…Both the efflux of harmful compounds out of the cell and their transport into the vacuole have the same benefit of removing dangerous toxic molecules from the cytosol and, thus, away from intracellular targets. In many cases, yeast ABCCs exhibit overlapping substrate specificity (144,145). The fact that both Ycf1p, a "full-length" ABCC transporter, and Yor1p, the plasma membrane-localized "short" transporter, can confer cadmium resistance (discussed in detail below) indicates that there is not a critical functional distinction between full-length and short ABCCs and that their distinct cellular locations may not necessarily confer unique properties (111).…”

“…Ycf1p plays an important role in the striking pink/red pigmentation of yeast colonies that arise from adenine biosynthetic mutants in yeast (144,145). Specifically, strains carrying ade1 or ade2 mutations accumulate an intense red pigment in their vacuoles when they are grown under conditions of adenine limitation.…”

“…Specifically, strains carrying ade1 or ade2 mutations accumulate an intense red pigment in their vacuoles when they are grown under conditions of adenine limitation. The formation of this pigment involves a series of steps, including the conjugation of the adenine biosynthetic intermediate phosphoribosylaminoimidazole (AIR) to GSH, the Ycf1p-dependent transport of AIR-GS into the vacuole, and further metabolism within the vacuole, ultimately giving rise to the familiar red pigment associated with an ade2 yeast strain (18,144,145). In a ycf1⌬ mutant, the pigmentation of an ade2 mutant colony is greatly diminished due to the significant lack of transport of AIR-GS into the vacuole.…”

“…In a ycf1⌬ mutant, the pigmentation of an ade2 mutant colony is greatly diminished due to the significant lack of transport of AIR-GS into the vacuole. The residual pigmentation in a ycf1⌬ mutant is due to a low level of transport activity mediated by two other ABCC transporters, Bpt1p and Ybt1p (144,145). The "red ade2 assay" has been used experimentally as a sensitive in vivo assay for the function of Ycf1p and/or its functional interactors (119).…”

Yeast ABC transporters – A tale of sex, stress, drugs and aging

“…The yeast cadmium factor (Ycf1p) mediates vacuolar detoxification of heavy metals and glutathione-S conjugates (GS-conjugates) [26][27][28][29], as well as red pigment accumulating in ade2 mutant cells [30]. Ycf1p is a yeast orthologue of mammalian MRPs, which have been implicated in MDR phenotypes of tumor cells, as well as in prominent genetic defects in hepatobiliary transport processes [1].…”