Structure and Helical Stability of a Modified Procollagen Synthesized in the Presence of 3,4-Dehydroproline

Abstract Tendons from 17-day-old chick embryos were incubated in medium containing 3,4-dehydro-l-proline, and a partially processed procollagen containing the car-boxyl-terminal but not the NH2-terminal propeptides (pCcollagen) was isolated from the incubation medium. In general, the amino acid composition of the altered pCcollagen was similar to that of normal type I pCcollagen. However, the isolated protein had a decreased content of hydroxyproline of about 33 residues/1000, a high content of hydroxylysine of 20 residues/1000, and about 9 residues/1000 of 3,4-dehydro-proline. In addition, the total imino acid content was about 38 residues/1000 less than that of normal pCcollagen, an observation which suggested that the proline analog increased the error rate of translation of proline codons. The protein was fully triple-helical at ambient temperatures as judged by circular dichroism, velocity sedimentation, and proteinase digestion. The midpoint of the triple-helix to random coil transition, however, was at 38.5 °C, or about 5° lower than that of normal pCcollagen obtained from the same source. Also, the temperature range for the helix to coil transition was broader. The results emphasize previous indications that the thermal stability of the triple-helix conformation of procollagen and collagen is not a simple function of the hydroxyproline and imino acid content of the protein.