Which protein prevents premature protein folding in the ER?
During insertion into endoplasmic reticulum, nascent polypeptide must remain in extended unfolded conformation to pass through narrow Sec61 channel approximately two nanometers wide and to allow domain-wise folding only after full entry into oxidizing, calcium-rich lumen favorable for disulfide formation and N-glycosylation. Premature formation of stable secondary structure, hydrophobic collapse or helical hairpins inside ribosome exit tunnel or within translocon would block progress and cause jamming requiring ribosome-associated quality control rescue. Lumenal chaperone BiP contributes to ho
Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 12: BiP Preventing Premature Folding.
