Altered Helical Structure of a Homotrimer of α1(I)Chains Synthesized by Fibroblasts from a Variant of Osteogenesis Imperfecta

• Published in: Collagen and related research Vol. 5; no. 4; pp. 305 - 313
• Main Authors: Deak, Susan B., Van Der Rest, Michel, Prockop, Darwin J.
• Format: Journal Article
• Language: English
• Published: 01.09.1985
• Subjects: trimers of α1(I) collagen; trimers of α1(I) collagen
• ISSN: 0174-173X
• DOI: 10.1016/S0174-173X(85)80020-0

Cultured skin fibroblasts from a variant of osteogenesis imperfecta were previously shown to synthesize a type I procollagen which was a homotrimer of proα1(I) chains. Trimers of α1(I) collagen were isolated by pepsin digestion of culture medium from these fibroblasts. The amino acid composition of the isolated protein indicated that it contained an increased amount of hydroxylysine, apparently because of post-translational over-modification. The thermal stability of the α1(I) trimers was examined by circular dichroism. We found no consistent difference in the melting curve of the α1(I) trimers compared to control type I collagen. We next examined the thermal stability of the α1(I) trimers using digestion with a combination of trypsin and α-chymotrypsin as an alternative probe of helical stability. When enzymatic digestions were carried out at 36° to 40°C, the α1(I) chains in the trimers were cleaved to polypeptides which were shortened by approximately 100 amino acids. Vertebrate collagenase digestion of the shortened molecules indicated that the 100 amino acid segment removed from each α1(I) chain was located at the carboxyl-terminus. The decreased thermal stability of the α1(I) trimers was probably explained by the absence of α2(I) chains in the molecules. The results, however, did not exclude the possibility that the post-translational over-modification of the α1(I) chains contributed to the altered helical structure.