Triple helix formation of procollagen type I can occur at the rough endoplasmic reticulum membrane

Triple helix formation of procollagen after the assembly of three α-chains at the C-propeptide is a prerequisite for refined structures such as fibers and meshworks. Hsp47 is an ER-resident stress inducible glycoprotein that specifically and transiently binds to newly synthesized procollagens. However, the real function of Hsp47 in collagen biosynthesis has not been elucidated in vitro or in vivo. Here, we describe the establishment of Hsp47 knockout mice that are severely deficient in the mature, propeptide-processed form of α1(I) collagen and fibril structures in mesenchymal tissues. The molecular form of type IV collagen was also affected, and basement membranes were discontinuously disrupted in the homozygotes. The homozygous mice did not survive beyond 11.5 days postcoitus (dpc), and displayed abnormally orientated epithelial tissues and ruptured blood vessels. When triple helix formation of type I collagen secreted from cultured cells was monitored by protease digestion, the collagens of Hsp47+/+ and Hsp47+/− cells were resistant, but those of Hsp47−/− cells were sensitive. These results indicate for the first time that type I collagen is unable to form a rigid triple-helical structure without the assistance of molecular chaperone Hsp47, and that mice require Hsp47 for normal development.

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Elucidation of proteostasis defects caused by osteogenesis imperfecta mutations in the collagen-α2(I) C-propeptide domain

Journal of Biological Chemistry ◽

10.1074/jbc.ra120.014071 ◽

2020 ◽

Vol 295 (29) ◽

pp. 9959-9973 ◽

Cited By ~ 1

Author(s):

Ngoc-Duc Doan ◽

Azade S. Hosseini ◽

Agata A. Bikovtseva ◽

Michelle S. Huang ◽

Andrew S. DiChiara ◽

...

Keyword(s):

Quality Control ◽

Endoplasmic Reticulum ◽

Osteogenesis Imperfecta ◽

Triple Helix ◽

Helix Formation ◽

Triple Helix Formation ◽

Triple Helices ◽

Triple Helical Domain ◽

Key Aspects ◽

Intracellular Collagen

Intracellular collagen assembly begins with the oxidative folding of ∼30-kDa C-terminal propeptide (C-Pro) domains. Folded C-Pro domains then template the formation of triple helices between appropriate partner strands. Numerous C-Pro missense variants that disrupt or delay triple-helix formation are known to cause disease, but our understanding of the specific proteostasis defects introduced by these variants remains immature. Moreover, it is unclear whether or not recognition and quality control of misfolded C-Pro domains is mediated by recognizing stalled assembly of triple-helical domains or by direct engagement of the C-Pro itself. Here, we integrate biochemical and cellular approaches to illuminate the proteostasis defects associated with osteogenesis imperfecta-causing mutations within the collagen-α2(I) C-Pro domain. We first show that “C-Pro-only” constructs recapitulate key aspects of the behavior of full-length Colα2(I) constructs. Of the variants studied, perhaps the most severe assembly defects are associated with C1163R C-Proα2(I), which is incapable of forming stable trimers and is retained within cells. We find that the presence or absence of an unassembled triple-helical domain is not the key feature driving cellular retention versus secretion. Rather, the proteostasis network directly engages the misfolded C-Pro domain itself to prevent secretion and initiate clearance. Using MS-based proteomics, we elucidate how the endoplasmic reticulum (ER) proteostasis network differentially engages misfolded C1163R C-Proα2(I) and targets it for ER-associated degradation. These results provide insights into collagen folding and quality control with the potential to inform the design of proteostasis network-targeted strategies for managing collagenopathies.

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