The hydrophobic domain 26 of human tropoelastin is unstructured in solution

Elastin is the protein responsible for the elastic properties of vertebrate tissue. Very little is currently known about the structure of elastin or of its soluble precursor tropoelastin. We have used high-resolution solution NMR methods to probe the conformational preferences of a conserved hydrophobic region in tropoelastin, domain 26 (D26). Using a combination of homonuclear, 15N-separated and triple resonance experiments, we have obtained essentially full chemical shift assignments for D26 at 278 K. An analysis of secondary chemical shift changes, as well as NOE and 15N relaxation data, leads us to conclude that this domain is essentially unstructured in solution and does not interact with intact tropoelastin. D26 does not display exposed hydrophobic clusters, as expected for a fully unfolded protein and commensurate with an absence of flexible structural motifs, as identified by lack of binding of the fluorescent probe 4,4′-dianilino-1,1′-binaphthyl-5,5′-disulfonic acid. Sedimentation equilibrium data establish that this domain is strictly monomeric in solution. NMR spectra recorded at 278 and 308 K indicate that no significant structural changes occur for this domain over the temperature range 278-308 K, in contrast to the characteristic coacervation behavior that is observed for the full-length protein.