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A structural mutation of the collagen alpha 1(I)CB7 peptide in lethal perinatal osteogenesis imperfecta
Insights
A structural defect in type I collagen's alpha 1(I)CB7 peptide causes lethal osteogenesis imperfecta in infants. This mutation leads to abnormal collagen structure and lysine overhydroxylation, impacting bone development.
Area of Science:
- Biochemistry
- Genetics
- Molecular Biology
Background:
- Osteogenesis imperfecta (OI) is a group of genetic disorders characterized by fragile bones.
- Type I collagen is the most abundant protein in bone and is crucial for skeletal integrity.
- Lethal perinatal osteogenesis imperfecta represents a severe form of the disease, often linked to critical collagen defects.
Purpose of the Study:
- To investigate the molecular basis of a specific lethal perinatal osteogenesis imperfecta case.
- To identify structural abnormalities in type I collagen and their functional consequences.
- To elucidate the inheritance pattern of the identified collagen defect.
Main Methods:
- Analysis of type I collagen from patient tissues (dermis, bone) and cultured fibroblasts.
- Two-dimensional gel electrophoresis of cyanogen bromide (CNBr) peptides to identify collagen chain abnormalities.
- Mammalian collagenase digestion to localize the structural defect within the alpha 1(I)CB7 peptide.
- Analysis of unhydroxylated collagens to assess potential mutations affecting sodium dodecyl sulfate (SDS) binding.
- Evaluation of post-translational hydroxylation of lysine residues in different collagen peptides.
Main Results:
- A heterozygous structural defect was identified in the alpha 1(I)CB7 peptide of type I collagen in a patient with lethal perinatal osteogenesis imperfecta.
- The mutation was localized to a 224-residue region at the NH2 terminus of the alpha 1(I)CB7 peptide.
- The mutant alpha 1(I)CB7 peptide showed altered migration on electrophoresis, suggesting a small deletion or mutation affecting SDS binding.
- Increased post-translational hydroxylation of lysine residues was observed in peptides near the NH2 terminus (CB7, CB3, CB8), but not the COOH-terminal CB6 peptide.
- The collagen defect was not detected in either parent, indicating a potential de novo mutation.
Conclusions:
- The identified structural defect in the alpha 1(I)CB7 peptide is a likely cause of lethal perinatal osteogenesis imperfecta.
- Lysine overhydroxylation in specific collagen peptides may result from the perturbation of helix propagation due to the structural defect.
- This defect disrupts collagen trimer formation and impacts skeletal development, leading to the severe phenotype observed.
Abstract:
Structurally abnormal type I collagen was identified in the dermis, bone, and cultured fibroblasts obtained from a baby with lethal perinatal osteogenesis imperfecta. Two-dimensional gel electrophoresis of the CNBr peptides demonstrated that the alpha 1(I)CB7 peptide from the alpha 1(I)-chain of type I collagen existed in a normal form and a mutant form with a more basic charge distribution. This heterozygous peptide defect was not detected in the collagens from either parent. The defect was localized to a 224-residue region at the NH2 terminus of the alpha 1(I)CB7 peptide by mammalian collagenase digestion. Analysis of unhydroxylated collagens produced in cell culture indicated that the mutant alpha 1(I)CB7 migrated faster on electrophoresis suggesting that the abnormality may be a small deletion or a mutation that alters sodium dodecyl sulfate binding. The post-translational hydroxylation of lysine residues was increased in the CB7 peptide and also in peptides CB3 and CB8 which are toward the NH2 terminus of the alpha 1(I)-chain. The COOH-terminal CB6 peptide was normally hydroxylated. These findings support the proposal that the lysine overhydroxylation resulted from a perturbation of helix propagation from the COOH to NH2 terminus of the collagen trimer caused by the structural defect in alpha 1(I)CB7.