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Two cysteine substitutions in procollagen I: a glycine replacement near the N-terminus of alpha 1(I) chain causes lethal osteogenesis imperfecta and a glycine replacement in the alpha 2(I) chain markedly destabilizes the triple helix.

ABSTRACT: Cultured skin fibroblasts were examined from two probands with type II (lethal) osteogenesis imperfecta. One proband had a single base mutation which converted the glycine codon at position alpha 1-244 in the alpha 1(I) chain of procollagen I into a cysteine codon whereas the other had a similar mutation that converted the glycine codon at position alpha 2-787 of the alpha 2(I) chain into a cysteine codon. Both mutations produced post-translational overmodification of procollagen I. The Cys alpha 1-244 mutation, however, had a minimal effect on the thermal stability or secretion of the protein whereas the Cys alpha 2-787 mutation markedly decreased the thermal stability and, apparently as a result, essentially none of the mutated protein was secreted. The results provide clear exceptions to two previous generalizations about the position-specificity of glycine substitutions in procollagen I.

SUBMITTER: Fertala A

PROVIDER: S-EPMC1132149 | biostudies-other | 1993 Jan

REPOSITORIES: biostudies-other

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Changes in collagen stability and folding in lethal perinatal osteogenesis imperfecta. The effect of alpha 1 (I)-chain glycine-to-arginine substitutions.

Project description:The effect of glycine-to-arginine mutations in the alpha 1 (I)-chain on collagen triple-helix structure in lethal perinatal osteogenesis imperfecta was studied by determination of the helix denaturation temperature and by computerized molecular modelling. Arginine substitutions at glycine residues 391 and 667 resulted in similar small decreases in helix stability. Molecular modelling suggested that the glycine-to-arginine-391 mutant resulted in only a relatively small localized disruption to the helix structure. Thus the glycine-to-arginine substitutions may lead to only a small structural abnormality of the collagen helix, and it is most likely that the over-modification of lysine, poor secretion, increased degradation and other functional sequelae result from a kinetic defect in collagen helix formation resulting from the mutation.

| S-EPMC1138808 | biostudies-other

Substitution of cysteine for glycine-alpha 1-691 in the pro alpha 1(I) chain of type I procollagen in a proband with lethal osteogenesis imperfecta destabilizes the triple helix at a site C-terminal to the substitution.

Project description:Skin fibroblasts from a proband with lethal osteogenesis imperfecta synthesized a type I procollagen containing a cysteine residue in the alpha 1(I) helical domain. Assay of thermal stability of the triple helix by proteinase digestion demonstrated a decreased temperature for thermal unfolding of the protein. Of special importance was the observation that assays of thermal stability by proteinase digestion revealed two bands present in a 2:1 ratio of about 140 and 70 kDa; the 140 kDa band was reducible to a 70 kDa band. Further analysis of the fragments demonstrated that the cysteine mutation produced a local unfolding of the triple helix around residue 700 and apparently exposed the arginine residue at position 704 in both the alpha 1(I) and alpha 2(I) chains. Analysis of cDNAs and genomic DNAs demonstrated a single-base mutation that changed the GGT codon for glycine-691 of the alpha 1(I) chain to a TGT codon for cysteine. The mutation was not found in DNA from either of the proband's parents. Since the proteinase assay of helical stability generated a fragment of 700 residues that retained disulphide-bonded cysteine residues at alpha 1-691, the results provide one of the first indications that glycine substitutions in type I procollagen can alter the conformation of the triple helix at a site that is C-terminal to the site of the substitution.

| S-EPMC1151509 | biostudies-other

Substitutions for arginine at position 780 in triple helical domain of the ?1(I) chain alter folding of the type I procollagen molecule and cause osteogenesis imperfecta.

Project description:OI is a clinically and genetically heterogeneous disorder characterized by bone fragility. More than 90% of patients are heterozygous for mutations in type I collagen genes, COL1A1 and COL1A2, and a common mutation is substitution for an obligatory glycine in the triple helical Gly-X-Y repeats. Few non-glycine substitutions in the triple helical domain have been reported; most result in Y-position substitutions of arginine by cysteine. Here, we investigated leucine and cysteine substitutions for one Y-position arginine, p.Arg958 (Arg780 in the triple helical domain) of pro?1(I) chains that cause mild OI. We compared their effects with two substitutions for glycine located in close proximity. Like substitutions for glycine, those for arginine reduced the denaturation temperature of the whole molecule and caused asymmetric posttranslational overmodification of the chains. Circular dichroism and increased susceptibility to cleavage by MMP1, MMP2 and catalytic domain of MMP1 revealed significant destabilization of the triple helix near the collagenase cleavage site. On a cellular level, we observed slower triple helix folding and intracellular collagen retention, which disturbed the Endoplasmic Reticulum function and affected matrix deposition. Molecular dynamic modeling suggested that Arg780 substitutions disrupt the triple helix structure and folding by eliminating hydrogen bonds of arginine side chains, in addition to preventing HSP47 binding. The pathogenic effects of these non-glycine substitutions in bone are probably caused mostly by procollagen misfolding and its downstream effects.

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Project description:We identified two infants with lethal (type II) osteogenesis imperfecta (OI) who were heterozygous for mutations in the COL1A1 gene that resulted in substitutions of aspartic acid for glycine at position 220 and arginine for glycine at position 664 in the product of one COL1A1 allele in each individual. In normal age- and site-matched bone, approximately 70% (by number) of the collagen fibrils were encrusted with plate-like crystallites of hydroxyapatite. In contrast, approximately 5% (by number) of the collagen fibrils in the probands' bone contained crystallites. In contrast with normal bone, the c-axes of hydroxyapatite crystallites were sometimes poorly aligned with the long axis of fibrils obtained from OI bone. Chemical analysis showed that the OI samples contained normal amounts of calcium. The probands' bone samples contained type I collagen, overmodified type I collagen and elevated levels of type III and V collagens. On the basis of biochemical and morphological data, the fibrils in the OI samples were co-polymers of normal and mutant collagen. The results are consistent with a model of fibril mineralization in which the presence of abnormal type I collagen prevents normal collagen in the same fibril from incorporating hydroxyapatite crystallites.

| S-EPMC1136074 | biostudies-other

Mutations in PPIB (cyclophilin B) delay type I procollagen chain association and result in perinatal lethal to moderate osteogenesis imperfecta phenotypes.

Project description:Recessive mutations in the cartilage-associated protein (CRTAP), leucine proline-enriched proteoglycan 1 (LEPRE1) and peptidyl prolyl cis-trans isomerase B (PPIB) genes result in phenotypes that range from lethal in the perinatal period to severe deforming osteogenesis imperfecta (OI). These genes encode CRTAP (encoded by CRTAP), prolyl 3-hydroxylase 1 (P3H1; encoded by LEPRE1) and cyclophilin B (CYPB; encoded by PPIB), which reside in the rough endoplasmic reticulum (RER) and can form a complex involved in prolyl 3-hydroxylation in type I procollagen. CYPB, a prolyl cis-trans isomerase, has been thought to drive the prolyl-containing peptide bonds to the trans configuration needed for triple helix formation. Here, we describe mutations in PPIB identified in cells from three individuals with OI. Cultured dermal fibroblasts from the most severely affected infant make some overmodified type I procollagen molecules. Pro?1(I) chains are slow to assemble into trimers, and abnormal procollagen molecules concentrate in the RER, and bind to protein disulfide isomerase (PDI) and prolyl 4-hydroxylase 1 (P4H1). These findings suggest that although CYPB plays a role in helix formation another effect is on folding of the C-terminal propeptide and trimer formation. The extent of procollagen accumulation and PDI/P4H1 binding differs among cells with mutations in PPIB, CRTAP and LEPRE1 with the greatest amount in PPIB-deficient cells and the least in LEPRE1-deficient cells. These findings suggest that prolyl cis-trans isomerase may be required to effectively fold the proline-rich regions of the C-terminal propeptide to allow pro? chain association and suggest an order of action for CRTAP, P3H1 and CYPB in procollagen biosynthesis and pathogenesis of OI.

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Project description:Glycine is required as every third residue in the collagen triple helix, and a missense mutation leading to the replacement of even one Gly in the repeating (Gly-Xaa-Yaa)(n) sequence with a larger residue leads to a pathological condition. Gly to Ala missense mutations are highly underrepresented in osteogenesis imperfecta (OI) and other collagen diseases, suggesting that the smallest replacement residue, Ala, might cause the least structural perturbation and mildest clinical consequences. The relatively small number of Gly to Ala mutation sites that do lead to OI must have some unusual features, such as greater structural disruption because of local sequence environment or location at a biologically important site. Here, peptides are used to model a severe OI case in which a Gly to Ala mutation is found within a highly stabilizing Lys-Gly-Asp sequence environment. Nuclear magnetic resonance, circular dichroism, and differential scanning calorimetry studies indicate this Gly to Ala replacement leads to a substantial loss of triple-helix stability and nonequivalence of the Ala residues in the three chains such that only one of the three Ala residues is capable of forming a good backbone hydrogen bond. Examination of reported OI Gly to Ala mutations suggests their preferential location at known collagen binding sites, and we propose that structural defects caused by Ala replacements may lead to pathology when they interfere with interactions.

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Osteogenesis imperfecta

Project description:Sequencing of a Fleckvieh animal for dominant Osteogensis imperfecta

| PRJEB12324 | ENA

Increased expression of the gene for the pro alpha 1(IV) chain of basement-membrane procollagen in cultured skin fibroblasts from two variants of osteogenesis imperfecta.

Project description:Fibroblasts from two lethal variants of osteogenesis imperfecta were shown to synthesize increased amounts of type IV procollagen. Previous studies established that one of these variants had a non-functional allele for the pro alpha 2 chain of type I procollagen, whereas the other pro alpha 2(I) allele contained a mutation leading to synthesis of shortened pro alpha 2(I) chains. In the two variants, the relative level of mRNA for pro alpha 1(IV) was 31 and 42% of the level of mRNA for pro alpha 1(I) chains. A value of less than 2% was found for a third lethal and four non-lethal variants of osteogenesis imperfecta. Immunofluorescent staining of fibroblasts from the two variants synthesizing increased amounts of type IV procollagen indicated that a homogeneous population of cells synthesized both type IV and type I procollagen. The results suggest that mutations in the type I procollagen genes that result in osteogenesis imperfecta can be associated with increased expression of the genes for type IV procollagen.

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Osteogenesis imperfecta.

Project description:Osteogenesis imperfecta is a phenotypically and molecularly heterogeneous group of inherited connective tissue disorders that share similar skeletal abnormalities causing bone fragility and deformity. Previously, the disorder was thought to be an autosomal dominant bone dysplasia caused by defects in type I collagen, but in the past 10 years discoveries of novel (mainly recessive) causative genes have lent support to a predominantly collagen-related pathophysiology and have contributed to an improved understanding of normal bone development. Defects in proteins with very different functions, ranging from structural to enzymatic and from intracellular transport to chaperones, have been described in patients with osteogenesis imperfecta. Knowledge of the specific molecular basis of each form of the disorder will advance clinical diagnosis and potentially stimulate targeted therapeutic approaches. In this Seminar, together with diagnosis, management, and treatment, we describe the defects causing osteogenesis imperfecta and their mechanism and interrelations, and classify them into five groups on the basis of the metabolic pathway compromised, specifically those related to collagen synthesis, structure, and processing; post-translational modification; folding and cross-linking; mineralisation; and osteoblast differentiation.

| S-EPMC7384887 | biostudies-literature

Osteoblast Malfunction Caused by Cell Stress Response to Procollagen Misfolding in ?2(I)-G610C Mouse Model of Osteogenesis Imperfecta.

Project description:Glycine (Gly) substitutions in collagen Gly-X-Y repeats disrupt folding of type I procollagen triple helix and cause severe bone fragility and malformations (osteogenesis imperfecta [OI]). However, these mutations do not elicit the expected endoplasmic reticulum (ER) stress response, in contrast to other protein-folding diseases. Thus, it has remained unclear whether cell stress and osteoblast malfunction contribute to the bone pathology caused by Gly substitutions. Here we used a mouse with a Gly610 to cysteine (Cys) substitution in the procollagen ?2(I) chain to show that misfolded procollagen accumulation in the ER leads to an unusual form of cell stress, which is neither a conventional unfolded protein response (UPR) nor ER overload. Despite pronounced ER dilation, there is no upregulation of binding immunoglobulin protein (BIP) expected in the UPR and no activation of NF-?B signaling expected in the ER overload. Altered expression of ER chaperones ?B crystalline and HSP47, phosphorylation of EIF2?, activation of autophagy, upregulation of general stress response protein CHOP, and osteoblast malfunction reveal some other adaptive response to the ER disruption. We show how this response alters differentiation and function of osteoblasts in culture and in vivo. We demonstrate that bone matrix deposition by cultured osteoblasts is rescued by activation of misfolded procollagen autophagy, suggesting a new therapeutic strategy for OI. © 2016 American Society for Bone and Mineral Research.

| S-EPMC5061462 | biostudies-literature

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