Collagen's enigmatic, highly conserved N-glycan has an essential proteostatic function.

Area of Science:

• Molecular Biology
• Cellular Biology
• Biochemistry

Background:

• Intracellular procollagen folding initiates in the C-terminal propeptide (C-Pro) domain, crucial for triple-helix assembly.
• The C-Pro domain contains a conserved N-glycosylation site, but its function in folding remained unclear as N-glycan removal did not affect wild-type collagen folding.
• Proteostasis, the maintenance of protein homeostasis, is vital for cellular function and is often challenged during physiological processes.

Purpose of the Study:

• To investigate the context-dependent function of the N-glycan on the procollagen C-Pro domain.
• To determine if the N-glycan plays a role in procollagen folding and secretion under conditions of cellular stress.

Main Methods:

• Utilized misfolding-prone variants of the C-Pro domain to assess the role of N-glycosylation.
• Compared folding and secretion efficiency of N-glycosylated versus non-N-glycosylated procollagen variants.
• Investigated the interaction of the N-glycan with the endoplasmic reticulum (ER) lectin-based chaperone machinery.
• Assessed procollagen folding and secretion under ER stress conditions.

Main Results:

• Removal of the N-glycan from misfolding-prone C-Pro variants led to significant procollagen and ER proteostasis defects.
• The N-glycan facilitates the folding and secretion of destabilized C-Pro variants by enabling interaction with ER chaperones.
• The C-Pro N-glycan is critical for wild-type procollagen folding and secretion, particularly under ER stress.

Conclusions:

• The N-glycan on the procollagen C-Pro domain has an essential, context-dependent function in buffering procollagen folding against proteostatic challenges.
• This carbohydrate moiety is critical for maintaining collagen production during cellular stress, relevant to development and wound healing.
• The findings elucidate the previously enigmatic role of the procollagen N-glycan in cellular proteostasis.