Triple-stranded helix, collagen

Among helical structures yet to be analyzed are the w and tt helices. Preliminary analyses have already been done on the polyproline I and polyproline 11 helices (Johnston, 1975), and these studies can provide the basis for a detailed analysis of the triple-stranded collagen helix. Since helices in proteins are found in short segments and often with distorted axes, it will be important to study the influence of such defects on the vibrational spectrum. 

Vitagliano, L., Nemethy, G., Zagari, A., and Scheraga, H. A. (1995). Structure of the type-I collagen molecule based on conformational energy computations The triple-stranded helix and the N-terminal telopeptide. / Mol. Biol. 247, 69-80. 

Fig. 4.5 Glycine residues make up the interior of a tropocollagen triple helix. The same three-stranded collagen super-helix is depicted as in Fig. 4.4, but looking down the center of a ball-and-stick representation. Glycine residues ( 11) are shown in red. Because of its small size, glycine is required where the three chains contact The balls in this illustration do not represent the van der Waals radii of the individual atoms (Figure 4-12d in Lehninger Principles of Biochemistry. D.L. Nelson and M.M. Cox, 4th Ed. 2005. W.H. Freeman Co., New York)...

Some natural fibrous proteins and sequential model polypeptides have been used as follows (1) Tussah Antheraea perni silk fibroin [a-helix form], (2) Bombyx mori silk fibroin [silk I and II forms], (3) poly(L-alanyL-glycine) [Ala-Gly]i2 [silk I and II], (4) collagen fibril [triple-strand helix], and (5) poly(L-prolyl-L-alanyL-glycine) [Pro-Ala-Gly [triple-strand helix]. 

Fig. 35. 300 MHz H CRAMPS NMR spectra of (A) [Pro-Ala-Glyjn (triple-stranded helix), and (B) collagen fibril (triple-stranded helix). Peak assignment H, 10-8 ppm side-chain phenyl, 8-7 ppm H of L-proline residue and H", 4.3-3.8 other side-chain protons, 1.6-1.9 ppm. 

Figure 27. Stereo pair plots of the collagen triple-stranded helix using the polytripeptide (l Pro-L Pro-Gly), coordinates of Miller and Scheraga [129].

Every third amino acid in the collagen chain is glycine. It is important to the structure because the triple-stranded helix forms as a result of interchain hydrogen bonding involving glycine. Thus, every third amino acid on one strand is in very close contact with the other two strands. Glycine has another... 

The collagens are the most abundant proteins found in various connective tissues of all multicellular animals. A typical collagen molecule has a long, flexible, and triple-stranded helical structure, in which three collagen polypeptide chains, so-called a-chains, are coiled in a rope-like helix. Among the 15 types of mature collagen molecules composed of different a-chains, the primary types are I, II, IV, and IX. 

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