Targeting Alanines in the Hydrophobic and Cross-Linking Domains of Native Elastin with Isotopic Enrichment and Solid-State NMR Spectroscopy

Details of elastin’s complex conformational and dynamic heterogeneity were acquired from one- and two-dimensional solid-state nuclear magnetic resonance (ssNMR) experiments on hydrated elastin that is isotopically enriched at its alanines. Elastin’s abundant alanines are useful probes of the structural and dynamical microenvironments in its cross-linking and hydrophobic domains. High isotopic enrichment of alanines in neonatal rat smooth muscle cells (NRSMC) elastin was obtained with the inhibition of alanine transaminase, combined with an excess of [U–13C]­alanine in the culture media. Due to the fast, large-amplitude motions, R-TOBSY was utilized with selective homonuclear decoupling schemes to resolve 13C-Ala peaks and confirm assignments. A data-driven approach is applied, as the interpretation of chemical shifts is based on the distribution of conformation-dependent 13C-Ala chemical shifts in proteins in multiple databases. Alanine populations in elastin’s hydrophobic domains are primarily random coil, whereas those in its cross-linking regions reside in α-helices and random coils.