Collagen structure

Kielty, C.M., Hopkinson, 1., Grant, M.E. Collagen structure, assembly and organization in the extracellular matrix. In Connective Tissue and its Heritable Disorders Wiley-Liss, Chichester, pp. 103-147, 1993. 

A number of rare genetic diseases involve collagen abnormalities, including Marfan s syndrome and the Ehlers-Danlos syndromes, which result in hyperextensible joints and skin. The formation of atheroselerotie plaques, which cause arterial blockages in advanced stages, is due in part to the abnormal formation of collagenous structures in blood vessels. 

The detection of the collagen-like threefold symmetric polypeptides, polyglycine4 and polyproline5, was the first help to elucidate the collagen structure using a synthetic peptide model. 

Gelse, K, Poschl, E., Aigner, T. (2003). Collagens - structure, function, and biosynthesis. Advanced Drug Delivery Reviews, Vol. 55, pp. 1531-1546. 

The ability of these peptidomimetic collagen-structures to adopt triple helices portends the development of highly stable biocompatible materials with collagenlike properties. For instance, it has been found that surface-immobilized (Gly-Pro-Meu)io-Gly-Pro-NH2 in its triple-helix conformation stimulated attachment and growth of epithelial cells and fibroblasts in vitro [77]. As a result, one can easily foresee future implementations of biostable collagen mimics such as these, in tissue engineering and for the fabrication of biomedical devices. 

Figure 48-1. Molecular features of collagen structure from primary sequence up to the fibril. (Slightly modified and reproduced, with permission, from Eyre DR Collagen Molecular diversity in the body s protein scaffold.Science 1980 207 1315. Copyright 1980 by the American Association for the Advancement of Science.)...

The cornea is the first structure of the eye to be in contact with incident light. It is composed of five distinct layers lying parallel to its surface the outer epithelium, which is continuous with the epithelial layers of the conjunctiva the epithelial basal lamina the keratocyte-containing stroma, which is a collagen structure arranged so that it is transparent Descemet s membrane and, finally, the endothelium adjacent to the aqueous humour. 

Johnstone, I.L. (1994) The cuticle of the nematode Caenorhabditis elegans - a complex collagen structure. BioEssays 16, 171-178. 

A few other helical conformations occur occasionally in globular protein structures. The polyproline helix, of the same sort as one strand out of a collagen structure, has been found in pancreatic trypsin inhibitor (Huber et al., 1971) and in cytochrome c551 (Almassy and Dickerson, 1978). An extended e helix has been described as occurring in chymotrypsin (Srinivasan et al., 1976). In view of the usual variability and irregularity seen in local protein conformation it is unclear that either of these last two helix types is reliably distinguishable from simply an isolated extended strand however, the presence of prolines can justify the designation of polyproline helix. 

MARCO macrophage receptor with collagenous structure... 

Vitamin C is essential for the formation of collagen, the principal structural protein in skin, bone, tendons, and ligaments, being a cofactor in the hydroxylation of the amino acids proline to 4-hydroxyproline, and of lysine to 5-hydroxylysine. These hydroxyamino acids account for up to 25% of the collagen structure. Vitamin C is also associated with some other hydroxylation reactions, e.g. the hydroxylation of tyrosine to dopa (dihydroxyphenylalanine) in the pathway to catecholamines (see Box 15.3). Deficiency leads to scurvy, a condition characterized by muscular pain, skin lesions, fragile blood vessels, bleeding gums, and tooth loss. Vitamin C also has valuable antioxidant properties (see Box 9.2), and these are exploited commercially in the food industries. 

Another example is the tissues that are particularly rich in vitamin C, for example, the cortex of the suprarenal gland or the lens here, vitamin C fulfills both antioxidative functions and metabolic ones as it helps in the formation of collagen structures. Approximately 40% of the body s ascorbate is stored in skeletal muscle because this tissue is relatively abundant and its cellular concentration is tenfold higher than the plasma level. Similarly, the intracellular ascorbate concentration in the brain (3 mM) greatly exceeds the level in the extracellular fluid (200-400 zM). The majority of ascorbate is stored in the astroglial cells that are capable of reducing great quantities of DHAA to ascorbate, which then becomes available for release back into the extracellular fluid. 

Vitamin C deficiency leads to impaired collagen production and defective collagen structure,... 

Athenstaedt,H. Permanent longitudinal electric polarization and pyroelectric behavior of collagenous structures and nervous tissue in man and other vertebrates. Nature 228, 830 (1970). 

Ramachandran, G. N., Bansal, M., and Bhatnagar, R. S. (1973). A hypothesis on the role of hydroxyproline in stabilizing collagen structure. Biochim. Biophys. Acta 322,166-171. 

McBride, D.J., Choe, V., Shapiro, J. R., and Brodsky, B. (1997). Altered collagen structure in mouse tail tendon lacking the alpha 2(1) chain./. Mol. Biol. 270, 275-284. Malone, J. P., George, A., and Veis, A. (2004). Type I collagen N-telopeptides adopt an ordered structure when docked to their helix receptor during fibrillogenesis. 

Ottani, V., Raspanti, M., and Ruggeri, A. (2001). Collagen structure and functional implications. Micron 32, 251-260. 

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