Hgt1p, a high affinity glutathione transporter from the yeast Saccharomyces cerevisiae

Abstract

A high affinity glutathione transporter has been identified, cloned, and characterized from the yeast Saccharomyces cerevisiae. This transporter, Hgt1p, represents the first high affinity glutathione transporter to be described from any system so far. The strategy for the identification involved investigating candidate glutathione transporters from the yeast genome sequence project followed by genetic and physiological investigations. This approach revealed HGT1 (open reading frame YJL212c) as encoding a high affinity glutathione transporter. Yeast strains deleted in HGT1 did not show any detectable plasma membrane glutathione transport, and hgt1Δ disruptants were non-viable in a glutathione biosynthetic mutant (gsh1Δ) background. The glutathione repressible transport activity observed in wild type cells was also absent in the hgt1Δ strains. The transporter was cloned and kinetic studies indicated that Hgt1p had a high affinity for glutathione (K_m = 54 μM)) and was not sensitive to competition by amino acids, dipeptides, or other tripeptides. Significant inhibition was observed, however, with oxidized glutathione and glutathione conjugates. The transporter reveals a novel class of transporters that has homologues in other yeasts and plants but with no apparent homologues in either Escherichia coli or in higher eukaryotes other than plants.