Regulation of protein synthesis: translational control by procollagen-derived fragments

Previous studies have shown that a type I procollagen-derived peptide, called pN alpha 1(I)-Col 1, selectively inhibits collagen synthesis by fibroblasts in culture and the translation of procollagen mRNA in a rabbit reticulocyte lysate system. We prepared the 10,700-dalton peptide from dermatosparactic calf skin, which contained high levels of incompletely processed type I procollagen, by collagenase digestion. Time-course and dose-response studies showed that the peptide specifically inhibited the translation of procollagen mRNA in preparations of human fibroblast RNA while not affecting the translation of globin mRNA or of other messenger RNAs in fibroblast RNA. After reduction and alkylation, the peptide lost its specificity but became a nonspecific inhibitor of translation. Enzymatic cleavage enabled us to localize the nonspecific activity to a short sequence -Pro-Thr-Asp-Glu, an assignment confirmed by peptide synthesis. Using pactamycin, a specific inhibitor of translational initiation, we showed that the intact peptide acts on procollagen mRNA translation by inhibition of polypeptide chain elongation or termination, or both, whereas the nonspecific inhibitory activity of the unfolded peptide and its derivatives can be attributed to an inhibition of chain initiation. Although the native peptide may function in feedback regulation of collagen synthesis, the physiological role of the lower molecular weight fragments, if any, is uncertain.