Direct Evidence of Imino Acid-Aromatic Interactions in Native Collagen Protein by DNP-Enhanced Solid-State NMR Spectroscopy.

Aromatic amino acids (AAAs) have rare presence (∼1.4% abundance of Phe) inside of collagen protein, which is the most abundant animal protein playing a functional role in skin, bone, and connective tissues. The role of AAAs is very crucial and has been debated. We present here experimental results depicting interaction of AAAs with imino acids in a native collagen protein sample. The interaction is probed by solid-state NMR (ssNMR) spectroscopy experiments such as (1)H-(13)C heteronuclear correlation (HETCOR) performed on a native collagen sample. The natural abundance (13)C spectrum was obtained by dynamic nuclear polarization (DNP) sensitivity enhancement coupled with ssNMR, providing ∼30-fold signal enhancement. Our results also open up new avenues of probing collagen structure/dynamics closest to the native state by ssNMR experiments coupled with DNP.