Abstract
The relationship between protein synthesis, folding, and disulfide formation within the endoplasmic reticulum (ER) is poorly understood. Previous studies have suggested that pre-existing disulfide links are absolutely required to allow protein folding and, conversely, that protein folding occurs prior to disulfide formation. To address the question of what happens first within the ER, that is, protein folding or disulfide formation, we studied folding events at the early stages of polypeptide chain translocation into the mammalian ER using stalled translation intermediates. Our results demonstrate that polypeptide folding can occur without complete domain translocation. Protein disulfide isomerase (PDI) interacts with these early intermediates, but disulfide formation does not occur unless the entire sequence of the protein domain is translocated. This is the first evidence that folding of the polypeptide chain precedes disulfide formation within a cellular context and highlights key differences between protein folding in the ER and refolding of purified proteins.
Highlights
The relationship between protein synthesis, folding, and disulfide formation within the endoplasmic reticulum (ER) is poorly understood
This is the first evidence that folding of the polypeptide chain precedes disulfide formation within a cellular context and highlights key differences between protein folding in the ER and refolding of purified proteins
The process of disulfide formation is intimately coupled with folding [4], and the rules and mechanisms dictating this process remain a central question in protein folding research
Summary
The authors declare that they have no conflict of interest. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Author’s Choice—Final version free via Creative Commons CC-BY license. To provide a suitable substrate to study early folding events and disulfide formation using stalled translation intermediates, we added a C-terminal polypeptide extension onto human 2M.
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