Heat shock protein 47 and 65-kDa FK506-binding protein weakly but synergistically interact during collagen folding in the endoplasmic reticulum

Abstract

Collagen is the most abundant protein in the extracellular matrix in humans and is critical to the integrity and function of many musculoskeletal tissues. A molecular ensemble comprising more than 20 molecules is involved in collagen biosynthesis in the rough endoplasmic reticulum. Two proteins, heat shock protein 47 (Hsp47/) and 65-kDa FK506-binding protein (FKBP65/), have been shown to play important roles in this ensemble. In humans, autosomal recessive mutations in both genes cause similar osteogenesis imperfecta phenotypes. Whereas it has been proposed that Hsp47 and FKBP65 interact in the rough endoplasmic reticulum, there is neither clear evidence for this interaction nor any data regarding their binding affinities for each other. In this study using purified endogenous proteins, we examined the interaction between Hsp47, FKBP65, and collagen and also determined their binding affinities and functions Hsp47 and FKBP65 show a direct but weak interaction, and FKBP65 prefers to interact with Hsp47 rather than type I collagen. Our results suggest that a weak interaction between Hsp47 and FKBP65 confers mutual molecular stability and also allows for a synergistic effect during collagen folding. We also propose that Hsp47 likely acts as a hub molecule during collagen folding and secretion by directing other molecules to reach their target sites on collagens. Our findings may explain why osteogenesis imperfecta-causing mutations in both genes result in similar phenotypes.

Roles of the endoplasmic reticulum–resident, collagen-specific molecular chaperone Hsp47 in vertebrate cells and human disease

“…These results suggest that Hsp47 and FKBP65 interact or work in very close proximity. Using purified endogenous proteins, interactions between Hsp47, FKBP65, and collagen were examined in vitro, and Hsp47 and FKBP65 were found to engage in a direct but weak interaction, whereas FKBP65 preferentially interacts with Hsp47 rather than type I collagen (93). Taken together, the findings indicate that FKBP65, LH2, and Hsp47 work together during procollagen maturation, contributing to the molecular stability and post-translational modification of type I procollagen.…”

Heme induces autophagic cell death via ER stress in neuron

“…The endoplasmic reticulum (ER) is an intracellular organelle where the protein molecule folding, transportation, or modification takes place and also a place for calcium storage, lipid synthesis, and carbohydrate metabolism [41,42,43]. Much evidences observed that the homeostasis of ER alters under certain pathological conditions leading to the accumulation of misfolded or unfolded proteins and ER stress.…”

Bone biology: insights from osteogenesis imperfecta and related rare fragility syndromes

“…not compete with HSP47-collagen interaction; when both proteins are present the collagen folding rate is increased, suggesting a role for HSP47 in favoring FKBP65-collagen interactions [96]. Mutations in either HSP47 or FKBP65 result in distinct forms of recessive osteogenesis imperfecta with overlapping phenotypes, characterized by increased or reduced telopeptide lysine hydroxylation, respectively [3,77,92].…”