Gly511 to Ser substitution in the COL1A1 gene in osteogenesis imperfecta type III patient with increased turnover of collagen.

Osteogenesis imperfecta (OI) is a result of heterozygous mutations in the COL1A1 or COL1A2 genes, encoding type I procollagen chains. Here we described the molecular and biochemical defects detected in a case of severe type III OI. Cultured skin fibroblasts from the proband produced both normal and mutant type I collagen which was secreted into the medium. The mutation site was localized in alpha 1(I)-CB3 by CNBr cleavage of collagen chains. Subsequent reverse transcription-PCR amplification and direct sequencing of single-stranded PCR product led to identification of G to A transition in the COL1A1 gene, resulting in Gly511Ser substitution in the a1 chain of type I collagen. The new mutation conforms to the chain-specific non-lethal microdomain of Gly to Ser substitutions in the genotype-phenotype map. We have found that biosynthesis of collagen was increased in OI cells to about 160% of the control value. However, the amount of collagen deposed to the insoluble matrix was decreased as compared to the control. This suggests increased degradation of collagen, since the collagenolytic activity of OI cells was increased. Furthermore, the activity of prolidase, which is a marker of collagen turnover, was increased in OI cells. In regulation of activity of the enzyme are involved beta1 integrin and insulin-like growth factor (IGF) receptors. Western immunoblot analysis showed that the expressions of both receptors were markedly increased in OI cells. These results suggest that increase in activity of prolidase can be associated with increase in intensity of collagen metabolism in type III OI patient with identified new G511S mutation.