Integrin alpha v beta 3 binds a unique non-RGD site near the C-terminus of human tropoelastin

Tropoelastin is the soluble precursor of the essential resilient connective tissue protein elastin. We examined the binding of integrin alpha(v)beta(3) to tropoelastin. In quantitative colorimetric solid-phase assays, purified alpha(v)beta(3) demonstrated saturable, divalent cation-dependent, single-site binding behavior on tropoelastin with a dissociation constant of 3.8 +/- 0.9 nM in the presence of 1 mM Mn(2+) which increased to 23 +/- 5 nM in the presence of 1 mM Ca(2+). Association with alpha(v)beta(3) was localized to the C-terminal 16 residues of tropoelastin, encompassing the region encoded by exon 36. This region comprises a unique disulfide loop in tropoelastin that is not essential for the interaction. This is the first identification of a specific, single binding site on tropoelastin and the first observation of direct binding of an integrin to a tropoelastin domain.