A-fibrous proteins

Collagen is the most abundant animal protein in the body of animals, where it makes up as much as one-quarter of all the proteins. It is a fibrous protein that provides structure to and protects and supports soft tissues it also connects tissues to the skeleton. Collagen forms, for example, most of the resilient layers that make up the skin and the filaments that support the internal organs. Interwoven with bioinorganic components, collagen also makes up the bones and teeth of vertebrate animals (see Chapter 15). 

Asbestos (or ferrunginous) bodies Nodular masses in the lung composed of collagen (a fibrous protein) and ferritin (an iron-containing globular protein). Although they... 

In addition to the 20 common amino acids, proteins may contain residues created by modification of common residues already incorporated into a polypeptide (Fig. 3-8a). Among these uncommon amino acids are 4-hydroxyproline, a derivative of proline, and 5-hydroxylysine, derived from lysine. The former is found in plant cell wall proteins, and both are found in collagen, a fibrous protein of connective tissues. 6-N-Methyllysine is a constituent of myosin, a contractile protein of muscle. Another important uncommon amino acid is y-carboxyglutamate, found in the bloodclotting protein prothrombin and in certain other proteins that bind Ca2+ as part of their biological function. More complex is desmosine, a derivative of four Lys residues, which is found in the fibrous protein elastin. 

Sheep s wool is made largely of keratin, a fibrous protein with an n-helical secondary structure. 

Silk is made of fibroin, a fibrous protein with a pleated-sheet secondary structure. 

Type C repeats are very common in proteins. They are quantal in length, but the repeats themselves do not contain residues that are conserved absolutely in any position. However, several positions within the repeats are strongly conserved in character. A classic example of a Type C repeat is that given by the heptad substructure in a-fibrous proteins. This has the form (a—b-c—d—e—f—g)n with the a and d positions generally occupied by apolar residues, and the e and g positions by charged or hydrophilic residues. The heptad is characteristic of an Q-helical conformation (Cohen and Parry, 1986, 1990 Lupas, 1996), but comparison of any two sequences with a heptad substructure generally reveals only about 15—20% identity. The motif also implies that several Q-helices will aggregate to form a multistranded left-handed coiled-coil rope to shield the apolar stripes on the surface of the Q-helices from the aqueous environment. 

Conway, J. F., and Parry, D. A. D. (1990). Structural features in the heptad substructure and longer range repeats of two-stranded a-fibrous proteins. Int. J. Biol. Macromol. 12, 328-334. 

Fibrinogen is a fibrous protein that was first classified with keratin, myosin, and epidermin based on its 5.1 A repeat in wide-angle X-ray diffraction patterns (Bailey et al., 1943), which was later discovered to be associated with the Q-helical coiled-coil structure. It is a glycoprotein normally present in human blood plasma at a concentration of about 2.5 g/L and is essential for hemostasis, wound healing, inflammation, angiogenesis, and other biological functions. It is a soluble macromolecule, but forms a clot or insoluble gel on conversion to fibrin by the action of the... 

Circular DNA is present in prokaryotes and in the mitochondria of eukaryotes. Collagen, a fibrous protein, and proteoglycans constitute the matrix in which cells are located. 

All except tropomyosin form larger molecules. Tubulin, under the influence of GTP, aggregates into microtubules G-actin polymerizes to F-actin myosin forms thick filaments by tail-to-tail interaction and /3-actin polymerizes to microfilaments. /3-Actin is similar but not identical to G-actin. Tropomyosin is a fibrous protein associated with the F-actin polymer. It controls myosin-actin interaction under the influence of troponin. 

Conchiolin is a fibrous protein similar to keratin that is found in mollusk shells, where it is mixed with calcium carbonate. 

The average hair is composed of about 90% keratin, a fibrous protein, and about 10% water. Each hair consists of two or three layers. The outer layer is a sheath called the cuticle, which is thin and colorless. It is made up of overlapping scales in layers. Inside the cuticle are the long spindle-shaped cells of the cortex, which makes up the bulk of the hair. These cells also contain whatever pigments are present in the hair. The innermost layer, which is only present in large thick hair, is the medulla or pith. 

Biochemists studying the structure of collagen (a fibrous protein in connective tissue) found cross-links containing... 

Crewther and Dowling at present take the view that the stability of a fibrous protein in a salt solution is determined largely by the number of sites available for hydration on ions bound by the fiber or absorbed as gegenions. The net charge on the fiber is important in that it determines the nature and number of gegenions absorbed. 

IR dichroism of globular proteins, a-fibrous proteins, insulin. 

Silk is a fibrous protein produced by several insect species. Commercially, silk is produced from the cocoon stage larvae of the moth caterpillar Bombyx mori, as it has been, in China, for some 4500 years. A single cocoon produces a continuous thread up to 1 km in length, and the protein fibroin contains large amounts of glycine, alanine, tyrosine, proline and serine The peptide chains are arranged in anti-parallel P-sheets which make up the hierarchical structure of the crystalline silk fibres. A number of spiders also produce silk webs, although the fibroin structure is rather different to that from silk worms. 

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