Elastin
Proteins

Author: Alessandra S
Date: 17/02/2012

Description
Elastin is a structural protein that provides elasticity in connective tissues. Elasticity is especially important for blood vessels and lung tissues, which have an expectedly high elastin content.

It is classed as a fibrous protein because of its structural function and relative insolubility in water. Elastin lacks a regular secondary structure. As in collagen, allysines form cross-links in elastin. An extracellular lysine amino oxidase converts lysine side chains in the sequence –Lys-Ala-Ala-Lys and –Lys-Ala-Ala-Ala-Lys to allysines. Three allysines and an unmodified lysine from different regions in the polypeptide chains react to form the heterocyclic structure of desmosine or isodesmosine, which cross-links the polypeptide chains in elastin networks.
The amino-acid composition of elastin is rich in proline and glycine, like that of collagen, but elastin does not have glycine as every third residue, nor does it have a triple-helical structure.
Instead, elastin is rich in alanine and valine.
A prototypical elastin sequence is Val–Pro–Gly–Val–Gly, and peptides composed of (Val–Pro–Gly–Val–Gly)n repeats are substrates for P4H.
The creation of Hyp in elastin is catalyzed by the collagen P4H, but there is less Hyp in elastin than in collagen and Hyp is not required for elastin biosynthesis or secretion

Proline in elastin-like polymers is efficiently hydroxylated under conditions where these polymers exhibit preferred secondary and tertiary structures.

Comments
2012-02-17T21:57:54 - Alessandra S

REGULATION OF ELASTIN BIOSYNTESIS BY ASCORBIC ACID

The accumulation of elastin is affected by levels of ascorbic acid. Cell cultures grown in the presence of ascorbate produce over-hydroxylated elastin that is less cross-linked and more soluble.
Apparently, Hyp levels affect the formation of elastin fibrils. Ascorbate dramatically affects insoluble elastin synthesis, accumulation, and cross-link formation.
Cells grown in the presence of ascorbate synthesize and accumulate significantly less insoluble elastin than non-ascorbate cultures.
Those elastin molecules which do become incorporated into the extracellular matrix in the presence of ascorbate contain a slightly elevated content of hydroxyproline and lysine and, most importantly, are turned over more rapidly. The amount of hydroxyproline accumulated in the cell layers grown in the presence of ascorbate is 2.5 times that present in the absence of ascorbate.

Effects of ascorbate on insoluble elastin accumulation and cross-link formation, 1982

Much less elastin is accumulated in the extracellular matrix of the ascorbate-treated cultures than in the matrix of those cultures not treated with ascorbate. The insoluble elastin matrix produced in the presence of ascorbate contains a somewhat higher content of hydroxyproline and lysine and slightly less lysine-derived cross-links than the non-ascorbate cultures.

Those highly hydroxylated elastin molecules which become bound to the matrix in spite of the presence of ascorbate probably cannot assume an appropriate fiber orientation for cross-link formation and thus can be more easily solubilized by either nonspecific proteolysis.
In the ascorbate-treated cultures the majority of the elastin molecules incorporated into the cell layer during the pulse period are not processed into the insoluble matrix via the normal cross-linking events. Interestingly enough, the portion of elastin in the ascorbate-treated cultures which remains insoluble does have reasonable levels of cross-links. This suggests that some tropoelastin units may not be as extensively hydroxylated as others and thus are capable of being cross-linked.

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