Fast time scale dynamics of protein backbones: NMR relaxation methods, applications, and functional consequences

The past 15 years saw an explosion of research on the dynamical properties of proteins. Much of these researches have been driven by the emergence of techniques sensitive to protein motion. One such technique is nuclear magnetic relaxation (NMR) which has now been applied to hundreds of proteins. Despite their many successes, NMR relaxation methods are plagued by a number of limitations and assumptions that make the functional interpretation of the data very difficult. This review focuses on the potential functional consequences of dynamics on a fast (picosecond-nanosecond) time scale. First, it presents a variety of ways in which fast time scale dynamics could potentially influence protein function. Second, it gives a summary of the theory behind protein backbone (15NH and 13CH) NMR relaxation methods and the relationship of relaxation to dynamics. Furthermore, it outlines an exhaustive list of previous NMR studies of backbone dynamics and discusses several of these studies in more detail, focusing on those for which there appear to be relationships between dynamics and function.