Solid-State NMR Spectroscopy and Isotopic Labeling Target Abundant Dipeptide Sequences in Elastin’s Hydrophobic Domains

Abstract

Isotopic labeling strategies are coupled with solid-state NMR spectroscopy to characterize elastin’s abundant glycines (Gly) and prolines (Pro) and the sequences that include these residues. Elastin is prepared with isotopic labels at Gly, Pro, and Val—three of its four most abundant amino acids. Solid-state 15N–1H nuclear magnetic resonance (NMR) spectra show four resolved glycine populations, whereas three features are observed for the prolines. Selection of the Val-Pro and Gly-Gly pairs found exclusively and abundantly in the hydrophobic domains confirms these assignments and also provides more information on the conformational ensembles of elastin. The 1HN and 15N temperature coefficients indicate that discrete secondary structures are present, even among significant populations with rapid conformational fluctuations typical of a random coil. 13C–15N couplings and the 13C chemical shift anisotropy (CSA) are also utilized to confirm assignments and structure, respectively. Implications for the evolving conformational ensemble model for elastin are also discussed.