Nuclear magnetic resonance (NMR) spectroscopy is at the core of current efforts to illuminate the nature and protein dynamics and their role in biological function. This review attempts to provide a complete description of the theoretical and technical foundation for solution NMR relaxation methods that are currently being brought to bear on fast sub-nanosecond protein side chain dynamics. A survey of basic observations about the side chain dynamics derived from NMR relaxation studies is presented along with several analyses meant to dispel commonly held but apparently inaccurate correlations between dynamics, structure, and function. How dynamics can enter into fundamental thermodynamic and kinetic aspects of proteion function is illustrated with results from several systems that point to promising future for this area of inquiry.
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