Elastin, amino acids

Amino acid CoUagen Elastin Keratin Albumin... 

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. 

Tropoelastin is the soluble precursor of elastin and consists of alternating hydrophobic and hydrophilic peptide domains. The most common amino acids in the hydrophobic domains are Gly, Val, Ala, and Pro, which are often present in repeats of tetra-, penta-, and hexapeptides, such as Gly-Gly-Val-Pro, Gly-Val-Gly-Val-Pro, Gly-Val-Pro-Gly-Val, and Gly-Val-Gly-Val-Ala-Pro, respectively [3, 4]. The hydrophilic domains are mainly composed of lysines interspersed by alanines. 

Fig. 15 Amino acid sequences of artificial extracellular matrix (aECM) proteins. Each protein contains a TV tag, a histidine tag, a cleavage site, and elastin-like domains with lysine residues for crosslinking. The RGD cell-binding domain is found in aECM 1, whereas aECM 3 contains the CS5 cell-binding domain. aECM 2 and aECM 4 are the negative controls with scrambled binding domains for aECM 1 and aECM 3, respectively. Reprinted from [121] with permission from American Chemical Society, copyright 2004...

Results of amino acid analysis performed on resilin from the locust Schistorcerca gregaria, compared with values for collagen, elastin, and silk fibroin. Reproduced from [145] with permission from Elsevier, copyright Elsevier 1961 Includes 106 hydroxyproline and 7 hydroxylysine... 

The fibrous protein elastin found extensively in connective tissues is unlike collagen in that it occurs in a less well ordered fashion, furthermore, there are quite marked differences seen between the chemical compositions of collagen and elastin. Whereas collagen comprises a very limited number of different amino acids, elastin contains a wider variety, the most abundant being glycine (approximately 30% dry weight), alanine (23%) valine (15%) and proline (12%). 

Figure 1 Design of a crosslinkable amino acid sequence based on the elastin-mimetic repeat Lys-25.

Keller S, Ghosh AK, Ghosh AK, Turino GM and Mandl I (1984) Separation of the cross-linking amino acids of elastin on thin-layer plates. J Chromatogr 305,461-464. 

Nakamura F, Yamazaki K and Suyama K (1992) Isolation and structural characterization of a new crosslinking amino acid, cyclopentenosine, from the acid hydrolysate of elastin. Biochem Biophys Res Comm 186, 1533-1538. 

Suyama K, Yamazaki K and Nakamura P (1995) Gyclopentenosine, trifunctional crosslinking amino acid of elastin and collagen, characterization and distribution. Spec Publ - R Soc Chem 151, 425. 

Elastin again seems to be made up of only three or four amino acids spongin is rather more complex. 

Calcium in this case would coordinate with acyl oxygens from the polypeptide backbone of the protein, because of its unique amino acid sequences and potential conformations348). Non-polar peptides have been isolated from elastin which consists almost entirely of the three non-polar amino acids glycine, valine, and proline349). Portions of porcine tropoelastin have been partially sequenced350). Repeating tetra-, penta-, and hexapeptides have been observed. The tetrapeptide contains the sequence —Gly—Gly—L—Val—L—Pro— the pentapeptide —L—Val—L—Pro-... 

Franzblau, C., Faris, B., Papaioannou, P. L. Lysinonorleucine. A new amino acid from hydrolyzates of elastin. Biochemistry 8, 2833 (1969)... 

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. 

Collagen and elastin are examples of common, well-characterized fibrous proteins that serve structural functions in the body. For example, collagen and elastin are found as components of skin, connective tissue, blood vessel walls, and sclera and cornea of the eye. Each fibrous protein exhibits special mechanical properties, resulting from its unique structure, which are obtained by combining specific amino acids into reg ular, secondary structural elements. This is in contrast to globular proteins, whose shapes are the result of complex interactions between secondary, tertiary, and, sometimes, quaternary structural elements. 

The tight y turn215 and the proline-containing P turn shown in Fig. 2-24 are thought to be major components of the secondary structure of elastin.216-218 This stretchable polymer, which consists largely of nonpolar amino acids, is the most abundant protein of the elastic fibers of skin, lungs, and arteries. The... 

Tissue also contains some endogenous species that exhibit fluorescence, such as aromatic amino acids present in proteins (phenylalanine, tyrosine, and tryptophan), pyridine nucleotide enzyme cofactors (e.g., oxidized nicotinamide adenine dinucleotide, NADH pyridoxal phosphate flavin adenine dinucleotide, FAD), and cross-links between the collagen and the elastin in extracellular matrix.100 These typically possess excitation maxima in the ultraviolet, short natural lifetimes, and low quantum yields (see Table 10.1 for examples), but their characteristics strongly depend on whether they are bound to proteins. Excitation of these molecules would elicit background emission that would contaminate the emission due to implanted sensors, resulting in baseline offsets or even major spectral shifts in extreme cases therefore, it is necessary to carefully select fluorophores for implants. It is also noteworthy that the lifetimes are fairly short, such that use of longer lifetime emitters in sensors would allow lifetime-resolved measurements to extract sensor emission from overriding tissue fluorescence. 

It occurred to have a broad primary specificity toward amino acids with hydrophobic side groups in synthetic ester and amide substrates. Pr2 exhibited rapid hydrolytic activity to casein and substrates containing Arg or Lys, while little or no activity was shown to cuticle, elastin, or substrates for chymotrypsin and elastase. The relation between Pr2 and trypsin was confirmed by the use of specific inhibitors. 

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