In eukaryotic cells, most newly synthesized secretory proteins are first translocated into the endoplasmic reticulum (ER) and transit through organelles that constitute a secretory pathway. However, a fraction of them never reach the desired native state. Instead, these proteins misfold in the ER and are retro-translocated out of this organelle to the cytoplasm, where they are degraded by the ubiqui-tin-proteasome system (a process called ER- associated degradation). For efficient retro-translocation, the disulfide bonds of misfolded proteins must be reduced, and on page 569 in this issue, Ushioda et al. (1) report that this reaction is catalyzed by ERdj5, the first dedicated reductase identified in the ER.
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