Schizosaccharomyces pombe ER oxidoreductin-like proteins SpEro1a p and SpEro1b p.

Endoplasmic reticulum oxidoreductins (Ero proteins) are essential for oxidation of protein disulphide isomerase (Pdi), which introduces disulphide bonds in target proteins. Contrary to the situation in Saccharomyces cerevisiae, with a single Ero protein (Ero1p), the genomes of Schizosaccharomyces pombe and of humans encode two Ero-like proteins. Here we show that both Sz. pombe proteins (SpEro1a p and SpEro1b p) are N-glycosylated and firmly associated with membranes of the secretory pathway. Surprisingly, only expression of SpEro1b p completely restores growth of the temperature-sensitive S. cerevisiae ero1-1 mutant, whereas SpEro1a p only partially complements this mutation. Upon expression in S. cerevisiae wild-type cells, SpEro1b p leads to a significantly increased resistance to reductive stress by dithiothreitol, whereas SpEro1a p has only a marginal effect. These data suggest that SpEro1b p is a functional homologue of the S. cerevisiae Ero1p.

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