Abstract
Triple helix formation of procollagen occurs in the endoplasmic reticulum (ER) where the single-stranded α-chains of procollagen undergo extensive post-translational modifications. The modifications include prolyl 4- and 3-hydroxylations, lysyl hydroxylation, and following glycosylations. The modifications, especially prolyl 4-hydroxylation, enhance the thermal stability of the procollagen triple helix. Procollagen molecules are transported to the Golgi and secreted from the cell, after the triple helix is formed in the ER. In this study, we investigated the relationship between the thermal stability of the collagen triple helix and environmental temperature. We analyzed the number of collagen post-translational modifications and thermal melting temperature and α-chain composition of secreted type I collagen in zebrafish embryonic fibroblasts (ZF4) cultured at various temperatures (18, 23, 28, and 33 °C). The results revealed that thermal stability and other properties of collagen were almost constant when ZF4 cells were cultured below 28 °C. By contrast, at a higher temperature (33 °C), an increase in the number of post-translational modifications and a change in α-chain composition of type I collagen were observed; hence, the collagen acquired higher thermal stability. The results indicate that the thermal stability of collagen could be autonomously tuned according to the environmental temperature in poikilotherms.
Highlights
Collagen is the most abundant protein in vertebrates
The number of 3-Hyp residues markedly increased only in collagen secreted from ZF4 cells at 33 ◦C (Figure 2, right). These results indicate that the increase in environmental temperature increases the number of post-translational modifications, but the temperature sensitivity was different according to modification types
Because the enzymes involved in procollagen post-translational modifications recognize only the single-stranded portions as substrate [12], the modifications should last until triple helix-formation is completed in the endoplasmic reticulum (ER)
Summary
Collagen is the most abundant protein in vertebrates. As the major component of the extracellular matrix, it plays roles in maintaining tissue structure and in regulating cellular functions. A total of 28 types of collagen have been identified in humans [1]. Type I collagen, the most abundant fibrillar collagen, has been well studied. Type I collagen has a triple-helical structure consisting of three polypeptide chains, called α-chains, containing > 1000 amino-acid residues. Each α-chain contains more than 330 repeats of the Gly-X-Y triplet, with approximately one-third of positions X and Y occupied by proline (Pro) and 4-hydroxyproline (4-Hyp) residues, respectively
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