Seo1p, a high affinity, plasma membrane transporter of the gamma-Glu-met dipeptide in yeasts and fungi

Abstract

{gamma}-Glu dipeptides are ubiquitous in nature, and yet their metabolism and transport are poorly understood. Here we investigate this using the dipeptide {gamma}-Glu-met in Saccharomyces cerevisiae. {gamma}-Glu-met was efficiently utilized by S. cerevisiae and its degradation was dependent on both the glutathione degrading cytosolic Dug2p/Dug3p complex, and the vacuolar Ecm38p. Using a transcriptomics approach, followed by a genetic screen, we identified Seo1p, an orphan transporter of yeast, as the transporter of {gamma}-Glu-met. Uptake studies confirmed Seo1p as a high affinity (Km =48uM), highly specific transporter of {gamma}-Glu-met since other analogs like n-Glu-met, {gamma}-Glu-leu, {gamma}-Glu-cys, {gamma}-Glu-met-gly, methionine and methionine sulfoxide were not transported by Seo1p. Candida spp. also encoded a functional Seo1p. A second transporter, Opt2p, identified in the screen, was also investigated. However, Opt2p was not primarily involved in {gamma}-Glu-met uptake. Its deletion affected vacuolar morphology, that interfered with the degradation of the peptide through Ecm38p. These studies demonstrate how organisms have evolved dedicated pathways for the uptake of these unusual peptides.