A dermatology researcher is studying the role of different amino acids in wound healing. She cultures mature dermal fibroblasts in growth media. After several days, the fibroblasts begin synthesizing polypeptide chains that assemble into triple helical structures, followed by fibrils. The fibrillar proteins are hydrolyzed and separated into their constituent amino acids via paper chromatography. Which of the following amino acids is most likely to be found in highest quantity in these proteins?
Collagen is the most abundant protein in the human body and is synthesized by fibroblasts, osteoblasts, and chondroblasts. It consists of 3 polypeptide alpha chains held together by hydrogen bonds, forming a rope-like triple helix (collagen molecule). Collagen molecules self-assemble into fibrils, which subsequently crosslink to form collagen fibers.
The triple helical conformation of collagen molecules occurs due to the simple and repetitive amino acid sequence within each alpha chain, in which glycine (Gly) occupies every third amino acid position (Gly-X-Y). Glycine is the most abundant amino acid in collagen and, due to its small size, is the only amino acid that can fit into the confined space between individual alpha chains.
(Choices A, B, D, E, and F) None of the other amino acids are as abundant as glycine in collagen. X often represents proline and Y is often hydroxyproline or hydroxylysine. Proline residues are essential for alpha helix formation because their ring configuration introduces a kink in the polypeptide chain, enhancing the rigidity of the helical structure. Hydroxylysine is necessary for cross-linking, which greatly increases the tensile strength of assembled collagen fibers.
Educational objective:
Glycine is the most abundant amino acid in collagen. The triple helical conformation of collagen molecules occurs due to the repetitive amino acid sequence within each alpha chain, in which glycine (Gly) occupies every third amino acid position (Gly-X-Y).