ReviewBiology of Hsp47 (Serpin H1), a collagen-specific molecular chaperone
Introduction
To perform their specific functions, nascent polypeptides must be folded into their three-dimensional native conformations. Molecular chaperones transiently interact with nascent polypeptides and promote the folding of polypeptides into their native conformations by preventing formation of protein aggregates [1]. The folding and stability of a protein’s native state are often challenged by the crowded cellular environment or the presence of genetic mutations that cause protein misfolding, leading to aggregate formation. In addition, protein homeostasis (proteostasis) is challenged by various cellular stresses, including heat shock and endoplasmic reticulum (ER) stress. These stresses lead to induction of cellular protective responses, including heat-shock response (HSR) in the cytosol and unfolded protein response (UPR) in the ER [1], [2]. Proteostasis is maintained by a network comprising molecular chaperones, transport machinery, the ubiquitin–proteasome system, and autophagic activities that function in concert to ensure the health of the proteome [3].
The ER is the major cellular site for the synthesis of membrane and secretory proteins, and is therefore equipped with the most elaborate protein quality control mechanisms. ER-resident chaperones, as well as several enzymes involved in folding and post-translational modification, assist with the various stages of protein maturation, including signal peptide cleavage, glycosylation, disulfide bond formation, and folding [4]. Glucose-regulated protein 78 (BiP/Grp78), a Hsp70 family protein, is the best-characterized ER-resident molecular chaperone. BiP is involved in many functions, including de novo protein folding and targeting of misfolded proteins to the ER-associated degradation (ERAD) machinery [5]. Various stresses in the ER (“ER stress”) result in induction of the UPR, whose downstream target genes boost the protein-folding capacity in the ER. Specifically, the UPR induces various ER-resident molecular chaperones involved in the refolding of misfolded proteins, as well as degradation of potentially toxic misfolded proteins [6], [7].
Heat-shock protein (Hsp) 47 is an ER-resident molecular chaperone that is essential for correct folding of procollagen in the ER [8]. Hsp47 has several distinctive characteristics; for example, other molecular chaperones (e.g., Hsp60, Hsp70, and Hsp90) have broad substrate specificity [9], whereas Hsp47 specifically binds to procollagens. Moreover, BiP and other ER-resident stress proteins are induced by ER stress, whereas Hsp47 is induced only by heat shock. Notably, the constitutive expression of Hsp47 is invariably correlated with expression of various types of collagens. Hsp47, which is encoded by the SERPINH1 gene, belongs to the serpin (serine protease inhibitor) superfamily, but it does not inhibit serine proteases [10].
Here, we review the role of Hsp47 in collagen folding in cells, the importance of Hsp47 in mouse development, and the clinical relevance of Hsp47 in various collagen-related diseases such as fibrosis.
Section snippets
Hsp47 is a collagen-specific molecular chaperone
Collagen is the most abundant mammalian protein, constituting approximately one-third of all protein in the human body. In particular, collagen is a major component of the extracellular matrix (ECM), which forms a specialized network around cells. Twenty-nine types of collagen have been identified to date [11].
Recent work has revealed the importance of collagen production during the aging process. During mammalian aging, most organs become smaller or thinner, and their functions and
Hsp47–collagen interaction
The interactions of recombinant mouse Hsp47 with collagens of types I–V were measured by surface plasmon resonance [43], yielding a dissociation constant of 10−6–10−7 M. This value, which was attributed to rapid dissociation and association, could reflect the transient interaction between Hsp47 and procollagen in the secretory pathway.
Hsp47 is a molecular chaperone specific to procollagen; by contrast, other molecular chaperones such as BiP and GRP94 have broad clients [44]. The primary
Structure of Hsp47
The collagen-binding site of Hsp47 was investigated in a nuclear magnetic resonance (NMR) study [53]. In particular, NMR spectroscopic analyses using a selective 15N-labeling method targeting Trp and His residues were performed in conjunction with site-directed mutagenesis. The results revealed that the B/C β-barrel domain and a nearby serpin loop in a 3D-homology model based on neuroserpin, a serpin family protein, constitute the collagen-binding site of chicken Hsp47. The structural
Phenotype of Hsp47 knockout
To elucidate the in vivo function of Hsp47, gene disruption was performed in mice using the homologous recombination technique [42]. Mice lacking Hsp47 did not survive beyond 11.5 days post coitus (dpc). At 10.5 dpc, the embryos of Hsp47−/−mice were still viable, but were much smaller than the wildtype, and they also contained fewer somites, suggesting developmental retardation. On the other hand, heterozygous Hsp47-knockout mice appeared phenotypically normal. In homozygous embryos, the mature,
Regulation of Hsp47 expression
Although many ER-resident chaperones are induced by accumulation of misfolded proteins in the ER, Hsp47 was discovered as a heat shock protein and is the only heat-inducible protein in the ER of mammalian cells. Hsp47 is not induced by ER stress response pathways such as the UPR. The heat inducibility of Hsp47 is mediated by a heat-shock element (HSE) located −180 bp from the transcription initiation site [33], [73], [74]. Upon cytoplasmic stresses such as heat shock or treatment with arsenite,
Hsp47 and disease
Hsp47 is a collagen-specific molecular chaperone that is essential for collagen synthesis. Accordingly, Hsp47 is intimately associated with collagen-related diseases including osteogenesis imperfecta (OI), keloid, and fibrosis.
OI is a genetic disorder characterized by bone fragility, bone deformity, growth deficiency, and shortened life span. Most cases with autosomal dominant inheritance are caused by mutations in type I collagen genes [85]. These mutations are associated with defective
Conclusions
Hsp47 (Serpin H1) is an ER-resident collagen-specific molecular chaperone that is essential for molecular maturation of collagen. Hsp47 binds Yaa-Gly-Xaa-Arg-Gly in triple-helical procollagen in the ER via hydrophobic and hydrophilic interactions. The binding of Hsp47 stabilizes procollagen by preventing unfolding of the triple helix and aggregate formation. Thus, Hsp47 is indispensable for efficient secretion, processing, fibril formation, and deposition of collagen in the ECM. Mutations in
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Research (S) (24227009) from the Japan Society for the Promotion of Science (JSPS) (to K.N.) and by Japan Society for the Promotion of Science (JSPS) Fellowships 11J05697 (to S. I.). We thank Yusaku Masago and Kunito Kawasaki for helpful discussion and preparation of the manuscript.
References (99)
- et al.
Protein quality control in the cytosol and the endoplasmic reticulum: brothers in arms
Mol. Cell
(2010) - et al.
BiP and its nucleotide exchange factors Grp170 and Sil1: mechanisms of action and biological functions
J. Mol. Biol.
(2015) - et al.
Hsp47 as a collagen-specific molecular chaperone
Methods Enzymol.
(2011) HSP47 as a collagen-specific molecular chaperone: function and expression in normal mouse development
Semin. Cell Dev. Biol.
(2003)- et al.
Procollagen traverses the Golgi stack without leaving the lumen of cisternae: evidence for cisternal maturation
Cell
(1998) - et al.
COPII – a flexible vesicle formation system
Curr. Opin. Cell Biol.
(2013) - et al.
The procollagen N-proteinases ADAMTS2 3 and 14 in pathophysiology
Matrix Biol.
(2015) - et al.
BMP-1/tolloid-like proteinases synchronize matrix assembly with growth factor activation to promote morphogenesis and tissue remodeling
Matrix Biol.
(2015) - et al.
A molecular ensemble in the rER for procollagen maturation
Biochim. Biophys. Acta
(2013) - et al.
Protein disulfide isomerase acts as a molecular chaperone during the assembly of procollagen
J. Biol. Chem.
(1998)
Quality control in the endoplasmic reticulum: PDI mediates the ER retention of unassembled procollagen C-propeptides
Curr. Biol.
Isolation of collagen binding proteins from embryonic chicken corneal epithelial cells
J. Biol. Chem.
The serpins are an expanding superfamily of structurally similar but functionally diverse proteins. Evolution, mechanism of inhibition, novel functions, and a revised nomenclature
J. Biol. Chem.
HSP47 binds cooperatively to triple helical type I collagen but has little effect on the thermal stability or rate of refolding
J. Biol. Chem.
Interactions between collagen-binding stress protein HSP47 and collagen. Analysis of kinetic parameters by surface plasmon resonance biosensor
J. Biol. Chem.
GRP94: an HSP90-like protein specialized for protein folding and quality control in the endoplasmic reticulum
Biochim. Biophys. Acta
Substrate recognition of collagen-specific molecular chaperone HSP47. Structural requirements and binding regulation
J. Biol. Chem.
Prediction of collagen stability from amino acid sequence
J. Biol. Chem.
Xaa-Arg-Gly triplets in the collagen triple helix are dominant binding sites for the molecular chaperone HSP47
J. Biol. Chem.
Sequence-specific recognition of collagen triple helices by the collagen-specific molecular chaperone HSP47
J. Biol. Chem.
Specific recognition of the collagen triple helix by chaperone HSP47. II. The HSP47-binding structural motif in collagens and related proteins
J. Biol. Chem.
Direct in vitro and in vivo evidence for interaction between Hsp47 protein and collagen triple helix
J. Biol. Chem.
Collagen stabilization at atomic level: crystal structure of designed (GlyProPro)10foldon
Structure
Nonlinear optical microscopy of articular cartilage
Osteoarthr. Cartil.
Intracellular trafficking and degradation of unassociated proalpha2 chains of collagen type I
Exp. Cell Res.
Proteasomal degradation of unassembled mutant type I collagen pro-alpha1(I) chains
J. Biol. Chem.
ERQC autophagy: yet another way to die
Mol. Cell
Phosphorylation and transformation sensitivity of a major collagen-binding protein of fibroblasts
J. Biol. Chem.
Homozygosity for a missense mutation in SERPINH1 which encodes the collagen chaperone protein HSP47, results in severe recessive osteogenesis imperfecta
Am. J. Hum. Genet.
Mutants of collagen-specific molecular chaperone Hsp47 causing osteogenesis imperfecta are structurally unstable with weak binding affinity to collagen
Biochem. Biophys. Res. Commun.
Molecular consequences of the SERPINH1/HSP47 mutation in the dachshund natural model of osteogenesis imperfecta
J. Biol. Chem.
Mechanisms of hepatic fibrogenesis
Gastroenterology
De novo design based pharmacophore query generation and virtual screening for the discovery of Hsp-47 inhibitors
Biochem. Biophys. Res. Commun.
Molecular chaperone functions in protein folding and proteostasis
Annu. Rev. Biochem.
Chemical and biological approaches for adapting proteostasis to ameliorate protein misfolding and aggregation diseases: progress and prognosis
Cold Spring Harb. Perspect. Biol.
Protein folding and quality control in the ER
Cold Spring Harb. Perspect. Biol.
Signalling pathways in the unfolded protein response: development from yeast to mammals
J. Biochem.
The unfolded protein response: from stress pathway to homeostatic regulation
Science
Global analysis of chaperone effects using a reconstituted cell-free translation system
Proc. Natl. Acad. Sci. U. S. A.
Variants in a novel epidermal collagen gene (COL29A1) are associated with atopic dermatitis
PLoS Biol.
Hair follicle aging is driven by transepidermal elimination of stem cells via COL17A1 proteolysis
Science
Dauer-independent insulin/IGF-1-signalling implicates collagen remodelling in longevity
Nature
Structural basis of fibrillar collagen trimerization and related genetic disorders
Nat. Struct. Mol. Biol.
The zipper-like folding of collagen triple helices and the effects of mutations that disrupt the zipper
Annu. Rev. Biophys. Biophys. Chem.
Global defects in collagen secretion in a Mia3/TANGO1 knockout mouse
J. Cell Biol.
Mechanisms for exporting large-sized cargoes from the endoplasmic reticulum
Cell. Mol. Life Sci.
Sedlin controls the ER export of procollagen by regulating the Sar1 cycle
Science
Sc65-null mice provide evidence for a novel endoplasmic reticulum complex regulating collagen lysyl hydroxylation
PLoS Genet.
Core glycosylation of collagen is initiated by two beta(1-O)galactosyltransferases
Mol. Cell. Biol.
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