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