Yeast Erv2p is the first microsomal FAD-linked sulfhydryl oxidase of the Erv1p/Alrp protein family

Saccharomyces cerevisiae Erv2p was identified previously as a distant homol ogue of Erv1p, an essential mitachondrial protein exhibiting sulfhydryl oxi dase activity. Expression of the ERV2 (essential for respiration and vegeta tive growth 2) gene from a high-copy plasmid cannot substitute for the lack of ERV1, suggesting that the two proteins perform nonredundant functions. Here, we show that the deletion of the ERV2 gene or the depletion of Erv2p by regulated gene expression is not associated with any detectable growth d efects. Erv2p is located in the microsomal fraction, distinguishing it from the mitochondrial Erv1p, Despite their distinct subcellular localization, the two proteins exhibit functional similarities. Both form dimers in vivo and in vitro, contain a conserved YPCXXC motif in their carboxyl-terminal p art, bind flavin adenine dinucleotide (FAD) as a cofactor, and catalyze the formation of disulfide bonds in protein substrates. The catalytic activity , the ability to form dimers, and the binding of FAD are associated with th e carboxyl-terminal domain of the protein. Our findings identify Erv2p as t he first microsomal member of the Erv1p/Alrp protein family of FAD-linked s ulfhydryl oxidases, We propose that Erv2p functions in the generation of mi crosomal disulfide bonds acting in parallel with Ero1p, the essential, FAD- dependent oxidase of protein disulfide isomerase.