Structure of the elastic fiber: an overview.

Intense research efforts over the past 18 yr have probed deeply into the structure of the elastic fiber. This began with the elucidation of the demosine crosslinks in elastin and the description of the elastin precursor, tropoelastin, derived from copper-deficient animals. Characterization of the precursor material indicates that it is a single polypeptide chain of approximately 800 amino acid residues containing lysine residues in clusters destined to form the desmosine crosslinks. The molecule contains large areas of hydrophobic sequence interspersed with shorter stretches of polyalanine and the lysines. The shorter structures may be folded into alpha-helices. The larger hydrophobic areas appear to form a unique structure known as the beta spiral which possesses elastometric properties. Inside the hydrophobic areas repeating sequences such as the pentapeptide pro-gly-val-gly-val have been observed the exact significance of which is not appreciated, but it appears to be well-conserved between species. Recent studies in the molecular biology of this protein have indicated that it is synthesized on the rough ER with a short leader sequence of about 25 residues. This is lost before the tropoelastin is exported. Diversity in sequence studies in these leaders suggest that there may be two elastins, type A and B, which vary with the maturation of the animal.