Direct observation of hierarchical protein dynamics

One of the fundamental challenges of physical biology is to understand the relationship between protein dynamics and function. At physiological temperatures, functional motions arise from the complex interplay of thermal motions of proteins and their environments. Here, we determine the hierarchy in the protein conformational energy landscape that underlies these motions, based on a series of temperature-dependent magic-angle spinning multinuclear nuclear-magnetic-resonance relaxation measurements in a hydrated nanocrystalline protein. The results support strong coupling between protein and solvent dynamics above 160 kelvin, with fast solvent motions, slow protein side-chain motions, and fast protein backbone motions being activated consecutively. Low activation energy, small-amplitude local motions dominate at low temperatures, with larger-amplitude, anisotropic, and functionally relevant motions involving entire peptide units becoming dominant at temperatures above 220 kelvin.