Molecular basis for the extensibility of elastin

Elastin is a cross-linked protein in the extracellular matrix that provides elasticity for many tissues. Its soluble precursor (tropoelastin) has two major types of alternating domains: (1) hydrophilic cross-linked domains rich in Lys and Ala and (2) hydrophobic domains (responsible for elasticity) rich in Val, Pro, and Gly, which often occur in repeats of VPGVG or VGGVG. Since native elastin is large and insoluble, many studies have focused on elastin-based peptides in an effort to elucidate its structure-function relationship. This review focuses on the molecular basis of elastin's conformational properties and associated elasticity. From both experimental and simulation approaches, elastin can be described as a two-phase model consisting of dynamic hydrophobic domains in water. The hydrophobic domain of elastin is best described as a compact amorphous structure with distorted P-strands, fluctuating turns, buried hydrophobic residues, and main-chain polar atoms that form hydrogen bonds with water. Water plays a critical role in determining elastin's conformational behavior, making elastin extremely dynamic in its relaxed state and providing an important source of elasticity.