Collagen structural protein

Bosse A, Ueda Y, Wuisman P, et al. Histogenesis of clear cell chondrosarcoma An immunohistochemical study with osteonectin, a non-collagenous structure protein. J Cancer Res Clin Oncol. 1991 117 43-49. 

Fujimoto, D. and Kenaya, S. (1973) Cuticulin a non-collagen structural protein from Ascaris cuticle. Arch. Biochem. Biophys. 157 1-6. 

Collagen Collagen is an extracellular structural protein 1052 amino acid residues. Collagen has an minsnal amino acid composidon it is about one-third glycine and is rich in proline. Note diat it also lacks Cys and Trp and is deficient in aromadc amino acid residues in general. 

Structural proteins u-Keratin Collagen Elastin Eibroin Proteoglycans... 

Resilin and elastin, unlike other structural proteins, fulfill both definitions of an elastic material. Colloquially speaking, resilin and elastin are stretchy or flexible. They also fulfill the strict definition of an elastic material, i.e., the ability to deform in proportion to the magnitude of an applied stress without a loss of energy, and the recovery of the material to its original state when that stress is removed. Resilin and elastin are alone in the category of structural proteins (e.g., collagen, silk, etc.) in that they have the correct blend of physical properties that allow the proteins to fulfill both definitions of elasticity. Both proteins have high extensibility and combine that property with remarkable resilience [208]. 

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 major components of the ECM are the structural proteins collagen, elastin, and fibrihin a number of specialized proteins (eg, fibronectin and laminin) and various proteoglycans. 

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. 

In living systems, proteins function as catalysts (enzymes), for defense (antibodies, immunoglobulins), signal transduction (hormones, receptors), metabolic regulation (hormones, enzymes, receptors, ion channels), movement (microtubules), and architecture (structural proteins such as collagen). 

So what does this magical molecule do Actually, it does two things, one rather more crystalline clear than the other. The crystal clear thing that ascorbic acid does is act as coenzyme for an enzyme known as prolyl hydroxylase. This enzyme catalyzes the conversion of the amino acid proline to hydroxyproline, a major, if exotic, amino acid in the structural protein collagen ... 

Protein turnover in an adult is about 4 to 5 g per kg body wt, equivalent to about 250 to 350 g of protein hydrolysed and resynthesised every day in the tissues of an adult human. This represents considerably more protein than is ingested in food. The rates of protein turnover vary enormously, depending on the nature of the protein, the condition of the subject and the tissue (Table 8.3). Proteins (mainly enzymes) in the liver are replaced every few hours or days whereas structural proteins (e.g. collagen, contractile proteins) are stable for several months. Contractile proteins can be degraded relatively rapidly in some conditions (see below). 

Macrophage release of chemotactic factors also attracts fibroblasts, an effect that has been studied in animals and humans. The factors are sufficiently strong and specific that fibroblasts migrate up a concentration gradient (tested in artificial chambers) and can induce replication (in vivo experiments). Thus, fibroblasts—the primary source of structural proteins, notably collagen— can be mobilized by AM to the inflammatory sites and can also markedly increase in number in response to secretion of activated AMs. These factors, in addition to the other activities and secretions of the AM, are being characterized (Gee, 1984). 

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. 

FIGURE 2.2 A diagram of human skin. Epidermal thickness depends upon body site being thickest on the palms and soles (-1500 pm) and thinnest around the eyes (-10 pm). The stratum corneum is the only layer composed of anucleated, terminally differentiated kerati-nocyte cells called corneocytes. All other epidermal layers contain nucleated keratinocytes. The dermis is composed primarily of the structural proteins collagen and elastin. 

Collagen is the major protein of the extracellular connective tissues and functions as a structural protein for many biomineralization processes, e. g. in bone and teeth. 

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