Collagen protein structural forces

The interaction between proteases and their inhibitors is, at least by comparison with interactions which take place in food systems, a remarkably simple and straightforward association. Simple correlations of functional properties with different kinds of molecular forces cannot be made. It is possible, however, to illustrate the importance of protein structure and of protein—protein interactions as determinants of the functional properties of food proteins. I would like therefore to look at several food systems in which protein—protein or protein—other constituent interactions play a role and examine the relationship between functionality and protein structure in these systems. One of the simplest areas in which to examine this relationship is the well studied collagen-gelatin transition. 

Another example of a peptide sequence in a protein forcing it into a biologically useful conformation is found with collagen. This consists of a triple helix with chains of more than 1000 amino-acid residues, many of which are post-translation-ally modified. The latter steps, consisting inter alia of hydroxylation of Pro and Lys residues and 5-hydroxylysine residues, occur before the triple helix is formed, because the enzymes involved do not act on the helical structure. When the individual peptide chains of collagen are synthesised, there are N- and C-terminal sequences each containing about 100 amino-acid residues. These sequences favour the formation of a triple helix. When this has been achieved, the terminal sequences are removed. The sequences of these temporary terminal sequences are quite different from the main body of the collagen monomers, which consists of triads of the type Gly—X—Y, where X and Y are often proline or 3- or 4-hydroxyproline. 

Schematic representation of the molecular organization of structural elements in cartilage matrix. Collagen fibrils provide tensile forces, and proteoglycans, because of their large solvent domains, accommodate reversible compressible forces. LP = link protein HA = hyaluronate KS = keratan sulfate CS = chondroitin sulfate PC = core protein. [Reproduced with permission from L. C. Junqueira, J. Carneiro, and J. A. Long, Basic Histology, 5th ed. Appleton Lange, Norwalk, CT, 1986. 1986 Appleton-Century-Crofts.]...

Collagen [77] is the principal protein constituent of a wide range of mammalian coimective tissue. It is a fibrous protein and the interest is interpreting its mechanical properties in terms of its chemical structure. Properties such as elastic moduli and stress-strain curves depend on the interatomic force constants so vibrational spectroscopy is a necessary... 

Contains an unusual ring to the N-end amine group, which forces the CO-NH amide sequence into a fixed conformation. Can disrupt protein folding structures like a-hetix or P sheet, forcing the desired kink in the protein chain. Common in collagen, where it often undergoes a posttranslational modification to hydroxyproline. Uncommon elsewhere. 

The media represents the major portion of the vessel wall and provides most of the mechanical strength necessary to sustain structural integrity. The media is organized into alternating layers of interconnected smooth muscle cells and elastic lamellae. There is evidence of coUagen throughout the media. These small collagen fibers are found within the bands of smooth muscle and may participate in the transfer of forces between the smooth muscle cells and the elastic lamellae. The elastic lamellae are composed principally of the fiberous protein elastin. The number of elastic lamellae depends upon the wall thickness and the anatomical location [12]. In the case of the canine carotid, the elastic lamellae account for a major component of the static structural response of the blood vessel [13]. This response is modulated... 

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