Collagen amide groups

Krimm, 1968a,b Mattice and Mandelkern, 1971 Krimm and Tiffany, 1974). This conformation is similar to that of a single strand from collagen, with average backbone dihedrals of (0,0) = ( 75°, +145°). These dihedrals lead to an extended left-handed helical conformation with precisely three residues per turn and 9 A between residues i and i + 3 (measured Cft to C/3). A cartoon of a seven-residue alanine peptide in this conformation is shown in Figure 1. Notably, backbone carbonyl and amide groups point perpendicularly out from the helical axis into the solvent and are well-exposed. 

Polar groups contribute greatly to adhesion of proteins to carbohydrates and to their cohesion. In denatured or unfolded proteins, such as animal glues, the peptide amide groups play an important role in adhesion but in the undenatured collagen, most peptide groups are associated in helical conformations. 

He had to discard his own elegant a-model, but with characteristic enthusiasm took up the implication of the planar amide group in the Pauling-Corey structures, considering it successively in relation to the models for wool, the cross /3-pattern, collagen, and feather keratin. 

The model reejuired that two-thirds of the total peptide bonds assume the m-configuration. Yet careful infrared absorption measurements (Badger and Pullin, 1954) showed that collagen contains very few, if any, CTS-amide groupings. Furthermore, Corey and Pauling (1953) themselves pointed out that the frawa-configuration is probably more stable than the... 

Scheme 4.19 The collagen triple helix (top) is stabilized by inter-strand hydrogen bridges between the peptide links of the backbone. Additional stabilization of the required trans proline substructures middle and below) can be derived from the gauche effect of strongly electronegative substituents X, for example hydroxy or fluorine, together with the electron-withdrawing amide group (X = H Pro, X = OH Hyp, X = F Fip) [50b, 51].

Definition Collagen which has been deamidated to modify amide groups to carboxylic acid groups Uses Film-former in cosmetics, providing skin elasticity and moisturizing props, to skin care prods. 

Photo 24 Linus Pauling working with a protein molecular model in the early 1950 s. The rectangular pieces of flat sheet metal represent the planar amide groups, so important in the structure of proteins (SP 105). The model represents Pauling and Corey s proposed structure for collagen (SP 103). 

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