Elastins

Elastin is hydrolyzed by the serine proteinase elastase, which is excreted by the pancreas. This enzyme preferentially cleaves peptide bonds at sites where the carbonyl residue has a nonaromatic, nonpolar side chain. 

Elastin is an insoluble, pol5mieric, extracellular matrix protein that provides the connective tissue in the body (skin, lungs, ligaments. 

Regarding the chemical cross-linking, various cross-linkers such as GA (Martino and Tamburro, 2001], disuccinimidyl glutarate (Martino and Tamburro, 2001], bis(sulfosuccinimidyl] suberate (Di Zio and Tirrell, 2003], copper sulfate and pyrroloquinoline quinone (Martino and Tamburro, 2001], ethylene glycol diglycidyl ether (Leach et al., 2005], hexamethylene diisocyanate (Nowatzki 

The basic unit of elastin structure is tropoelastin, which has a molecular weight of about 72,000 and contains 800-850 amino acid residues. It has been proposed that tropoelastin units are present in the random coil conformation and are extensively cross-linked. This makes such a network kinetically free free to stretch and to recoil. It is the entropy effects that permit the stretched elastin 

Although it is extremely difficult to blend elastin with synthetic polymers, it forms an excellent basis for biomaterials, such as dermal substitute, arterial prosthesis, hydrogels, and for scaffolds [38-42]. 

Q Signal peptide fl KP domains Q KA domains 0 Hydrophobic domains 

Tropoelastin molecules that have lost their chaperone 

Cross-linking of the tropoelastin molecules within the tropoelastin-fibrillin aggregates is mediated by lysyl oxidase, the same enzyme responsible for cross-linking collagen fibers. In the KA domains, lysine residues are typically found in clusters of two or three amino acids, separated by two or three alanine residues. These regions are proposed to be a-helical with 3.6 residues per turn of helix, which has the effect of positioning two lysine 

The hydrophobic domain of elastin is a compact, dynamic structure which forms shortlived interconverting structures distorted (3 strands, fluctuating (3 turns, and buried hydro-phobic residues. Nevertheless, the numerous amide groups in the peptide bonds can still hydrogen bond with water. The overall structure is therefore a compact amorphous 

Elastin is synthesized and secreted mostly during early development and it has a half-life of 70 years. Otherwise, it is only made after an injury or infection, which induces white blood cells, especially neutrophilic granulocytes (neutrophils) to the site (Sect. 13.2.3). One of the many proteolytic products of neutrophils is elastase (Sect. 8.3.1), which hydrolyzes elastin at sites between the cross-linked region. Cleavage is most common on the C-terminal side of valine bonded to alanine (i.e., between val-ala residues). 

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Scieroproteins. Insoluble proteins obtained from the skeletal and connective tissues of animals. Typical classes are keratins collagens and elastin classes. 

Chemical Composition. From the point of view of leathermaking, hides consist of four broad classes of proteins coUagen, elastin, albumen, and keratin (3). The fats are triglycerides and mixed esters. The hides as received in a taimery contain water and a curing agent. Salt-cured cattie hides contain 40—50% water and 10—20% ordinary salt, NaCl. Surface dirt is usuaUy about 2—5 wt %. Cattie hides have 5—15% fats depending on the breed and source. The balance of the hide is protein (1). 

Amino acid CoUagen Elastin Keratin Albumin... 

Albumen has the largest number of acid and basic groups. It is the most soluble of the proteins present in a hide. The albumen is not a fibrous material, however, and therefore has no value in the leather. Keratin is the protein of the hair and the outermost surface of the hide. Unless the hair is desired for the final product it is removed by chemical and/or physical means. The elastin has Htde acid- or base-binding capacity and is the least soluble of the proteins present. The lack of reactivity of the elastin is a detriment for most leather manufacture. The presence of elastin in the leather greatly limits the softness of the leather. 

Airway cross-sections have the nominal anatomy shown in Fig. 5.16. Airway surface liquid (AST), primarily composed of mucus gel and water, surrounds the airway lumen with a thickness thought to vary from 5 to 10 mm. AST lies on the apical surface of airway epithelial cells (mostly columnar ciliated epithelium). This layer of cells, roughly two to three cells thick in proximal airways and eventually thinning to a single cell thickness in distal airways, rests along a basement membrane on its basal surface. Connective tissue (collagen fibers, basement membranes, elastin, and water) lies between the basement membrane and airway smooth muscle. Edema occurs when the volume of water within the connective tissue increases considerably. Interspersed within the smooth muscle are respiratory supply vessels (capillaries, arteriovenous anastomoses), nerves, and lymphatic vessels. 

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

One intensively investigated feature of the inflammatory process in COPD is the release of proteases from neutrophils and monocytic cells that destroy elastin and other components of the interstitial matrix (Table 1). The best studied protease is neutrophil elastase. Independent of its elastolytic activity, neutrophil elastase is a potent secretagogue. More recently matrix metalloproteases (MMP) have received increasing attention, in particular MMP 12 (macrophages elastase). To which extent and how exactly these proteases become activated is not clear at present. 

Elizabeth et al. [108] reported an elastin-mimic polypeptide sequence that mimics triblock copolymers (ABA) with the sequence of the respective blocks as... 

Wright E.R., McMillan R., Andrew C.A., Apkarian, R.P., and Conticello, V.P. Thermoplastic elastomer hydrogels via self-assembly of an elastin-mimetic triblock polypeptide, Adv. Func. Mater., 12, 149, 2002. 

Urry D.W., Whai is elastin what is not, Ultrastructural Pathology, 4, 227, 1983. 

Lee T.A.T., Cooper A., Apkarian R.P., and Conticello V.P. Thermo-reversible self-assembly of nano-particles derived from elastin-mimetic polypeptides. Advanced Materials, 12, 1105, 2000. 

A star copolymer (SCP) of PCLA was synthesized by Younes and coworkers. This kind of SCP PCLA elastomer was also synthesized in two steps. First, the small molecular SCP was produced by ring-opening polymerization of s-caprolactone (s-CL) with glycerol as initiator and stannous 2-ethyUiexanoate as catalyst. Second, the living SCP was further reacted with different ratios of a cross-linking monomer, such as 2,2-bis(s-CL-4-yl)-propane (BCP) and s-CL. The SCP elastomers had very low glass transition temperature (—32°C). It was reported that the SCPs were soft and weak with physical properties similar to those of natural bioelastomers such as elastin. A logarithmic decrease in each tensile property with time was observed in this SCP PCLA. 

Coacervation occurs in tropoelastin solutions and is a precursor event in the assembly of elastin nanofibrils [42]. This phenomenon is thought to be mainly due to the interaction between hydro-phobic domains of tropoelastin. In scanning electron microscopy (SEM) picmres, nanofibril stmc-tures are visible in coacervate solutions of elastin-based peptides [37,43]. Indeed, Wright et al. [44] describe the self-association characteristics of multidomain proteins containing near-identical peptide repeat motifs. They suggest that this form of self-assembly occurs via specific intermolecular association, based on the repetition of identical or near-identical amino acid sequences. This specificity is consistent with the principle that ordered molecular assembhes are usually more stable than disordered ones, and with the idea that native-like interactions may be generally more favorable than nonnative ones in protein aggregates. 

Rousseau, R., Schreiner, E., Kohbneyer, A., and Marx, D., Ternperamre-dependent conformational transitions and hydrogen-bond d3mamics of the elastin-bke octapeptide GVG(VPGVG) A molecular-dynamics study, Biophys. J., 86, 1393-1407, 2004. 

Pometun, M.S., Chekmenev, E.Y., and Wittebort, R.J., Quantitative observation of backbone disorder in native elastin, J. Biol. Chem., 279, 7982-7987, 2004. 

Miao, M., Cimlis, J.T., Lee, S., and Keeley, F.W., Stmctural determinants of cross-hnking and hydro-phobic domains for self-assembly of elastin-hke pol3fpeptides. Biochemistry, 44(43), 14367-14375, 2005. 

Keeley, F.W., Bellingham, C.M., and Woodhouse, K.A., Elastin as a self-organising biomaterial Use of recombinantly expressed human elastin polypeptides as a model system for investigations of structure and self-assembly of elastin, Philos. Trans. R. Soc. Lond. B Biol. Sci., 357, 185-189, 2002. 

Belhngham, C.M., Lillie, M.A., Gosline, J.M., Wright, G.M., Starcher, B.C., Bailey, A.J., Woodhouse, K.A., and Keeley, F.W., Recombinant human elastin polypeptides self-assemble into biomaterials with elastin-hke... 

Aaron, B.B. and Gosline, J.M., Elastin as a random-network elastomer A mechanical and optical analysis of single elastin fibers. Biopolymers, 20, 1247-1260, 1980. 

Patients of varying skin types (1-V) having striae distensae alba on the abdomen or thighs can apply topical 20% glycolic acid daily to the entire treatment area. In addition, these patients apply 10% L-ascorbic acid, 2% zinc sulfate, and 0.5% tyrosine to half of the treatment area and 0.05% tretinoin emollient cream to the other half of the treatment area. The creams are applied on a daily basis for 12 weeks. Improvement is evaluated at 4 and 12 weeks with increased elastin content within the reticular and papillary dermis [14]. 

Keywords Elastin Elastin-like polypeptides Elastomeric polypeptides Resilin Resilin-like polypeptides... 

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