A solution NMR view of protein dynamics in the biological membrane.

Structure determination of membrane-associated proteins (MPs) represents a frontier of structural biology that is characterized by unique challenges in sample preparation and data acquisition. No less important is our ability to study the dynamics of MPs, since MP flexibility and characteristic motions often make sizeable contributions to their function. This review focuses on solution state NMR methods to characterize dynamics of MPs in the membrane environment. NMR approaches to study molecular motions on a wide range of time-scales and their application to membrane proteins are described. Studies of polytopic and bitopic MPs demonstrating the power of such methods to characterize the dynamic behavior of MPs and their interaction with the membrane-mimicking surroundings are presented. Attempts are made to place the dynamic conclusions into a biological context. The importance and limitations of such investigations guarantee that further developments in this field will be actively pursued.