tropoelastin

Tropoelastin is the soluble monomeric precursor of elastin, encoded by the ELN gene on chromosome 7 in humans. It is produced primarily by fibroblasts and vascular smooth muscle cells and is secreted into the extracellular matrix, where it participates in the formation of elastic fibers that confer resilience and stretch to tissues.

Structurally, tropoelastin is a single polypeptide of roughly 700–800 amino acids with a modular composition that includes alternating hydrophobic domains and lysine-rich cross-linking regions. The hydrophobic segments often contain repeats such as valine-proline-glycine-valine-proline-glycine (VPGVG), which contribute to elasticity, while the cross-linking domains provide sites for covalent bonding during fiber formation.

Elastin fibers are formed extracellularly through assembly of tropoelastin onto a scaffold of microfibrils, particularly those rich in fibrillin-1. Lysyl oxidase initiates cross-linking by deaminating lysine residues, enabling desmosine and isodesmosine cross-links between tropoelastin molecules. This cross-linking transforms soluble tropoelastin into insoluble, resilient elastin within mature fibers.

Regulation and tissue distribution of tropoelastin expression are influenced by factors such as transforming growth factor-β, mechanical stretch, and hormonal signals. Tropoelastin is abundant in skin, lungs, large arteries, ligaments, and other elastic tissues. It is produced by mesenchymal cells, including fibroblasts and vascular smooth muscle cells, and can be degraded by elastases under aging or disease conditions.

Clinical relevance includes defects in elastogenesis due to ELN mutations, which can cause cutis laxa and supravalvular aortic stenosis. Elastin integrity is essential for vascular compliance and tissue recoil, and age-related elastin degradation contributes to decreased tissue elasticity. Tropoelastin is also explored in biomaterials research for elastic hydrogel applications.