Elastin amino acid residue repeating

Mature elastin is a linear polypeptide, tropoelastin, which has a molecular weight of about 72,000 and contains about 850 amino acid residues. Although glycine accounts for one third of the residues, the repeat sequence Gly-X-Y characteristic of collagen is not present in elastin. Instead, glycine residues are present in the repeat units Gly-Gly-Val-Pro, Pro-Gly-Val-Gly-Val, and Pro-Gly-Val-Gly-Val-Ala. Elastin is relatively rich in the nonpolar amino acids alanine, valine, and proline. In contrast to collagen, only a few hydroxyproline residues are present in elastin. Elastin contains no hydroxylysine or sugar residues. 

Elastin is Cross-linked and Contains Repeating Sequences of Amino Acid Residues... 

The other major protein in the extracellular matrix is elastin, which is the main component of elastic fibers found in ligaments, large arteries, and lungs. After synthesis and partial hydroxylation of proline residues, a 72 kDa molecule of tropoelastin is secreted into the matrix. This protein is rich in nonpolar amino acids and contains repeating sequences, such as (Val-Pro-Gly-Val-Gly). These sections form an amorphous, random-coiled structure with frequent reverse turns. Other recurrent sequences are rich in alanine with paired lysine residues, e.g., -Ala-Ala-Ala-Ala-Lys-Ala-Ala-Lys-... 

Amino acid sequences of specific tryptic peptides found in porcine tropoelastin. When tentative assignments are given, the designations are in parentheses. The common repeating units are underlined. In certain instances liberty was taken in defining a common repeating unit when there was only amino acid difference. These sequences are common to the extensible regions in elastin. The tetra, penta or hexa repeats appear to correspond to 15 to 25 percent of the total residues in the protein. The source for the sequence data is reference 1. 

Figure 3 (a) Comparison of the turbidimetric profiles for a series of chemosynthetic elastin polypeptides based on random copolymers of the repeat sequence [(Val-Pro-Gly-Val-Gly)i x(Val-Pro-Gly-Xaa-Gly)J, where fx refers to the mole fraction of variant pentapeptides within the polymer sequence. " (b) Hydrophobicity scale based on ft values for the copolymers described above as a function of guest residue identity and mole fraction, f. Note that hydrophobic amino acids shift the position of 7 toward lower temperature and that more polar guest residues shift the position of 7i toward higher temperatures in a manner commensurate with the level of substitution within the polypeptide sequence. Reprinted from Uriy, D. W. Gowda, D. C. Parker, T. M. etal. Biopolymers 99Z, 32(9), 1243 20(b) Copyright 1992, with permission from Wiley. 

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