Structural and Functional Study of Yer067w, a New Protein Involved in Yeast Metabolism Control and Drug Resistance

The genome of Saccharomyces cerevisiae is arguably the best studied eukaryotic genome, and yet, it contains approximately 1000 genes that are still relatively uncharacterized. As the majority of these ORFs have no homologs with characterized sequence or protein structure, traditional sequence-based approaches cannot be applied to deduce their biological function. Here, we characterize YER067W, a conserved gene of unknown function that is strongly induced in response to many stress conditions and repressed in drug resistant yeast strains. Gene expression patterns of YER067W and its paralog YIL057C suggest an involvement in energy metabolism. We show that yeast lacking YER067W display altered levels of reserve carbohydrates and a growth deficiency in media that requires aerobic metabolism. Impaired mitochondrial function and overall reduction of ergosterol content in the YER067W deleted strain explained the observed 2- and 4-fold increase in resistance to the drugs fluconazole and amphotericin B, respectively. Cell fractionation and immunofluorescence microscopy revealed that Yer067w is associated with cellular membranes despite the absence of a transmembrane domain in the protein. Finally, the 1.7 angstrom resolution crystal structure of Yer067w shows an alpha-beta fold with low similarity to known structures and a putative functional site. YER067W's involvement with aerobic energetic metabolism suggests the assignment of the gene name RGI1, standing for respiratory growth induced 1. Altogether, the results shed light on a previously uncharacterized protein family and provide basis for further studies of its apparent role in energy metabolism control and drug resistance.