Understanding Protein Function Through an Ensemble Description: Characterization of Functional States by 19F NMR.

Protein function is a consequence of a complex and dynamic equilibrium between allosterically coupled functional states. However, it is often difficult to distinguish the representative members of an ensemble by spectroscopic means. 19F NMR is particularly useful in this regard owing to the sensitivity of its chemical shift to subtle differences in environment. Here, we address aspects of 19F NMR relevant to the study of ensembles. In particular, we discuss current trends toward: (1) 19F-reporters that can be biosynthetically incorporated into proteins, (2) Approaches to chemical tagging of proteins by 19F reporters, (3) Improving delineation of states by 19F NMR, (4) Distinguishing states by (19F NMR-based) topology measurements that focus on solvent exposure and hydrophobicity, (5) Relaxation experiments and simple approaches to delineating states in fast and slow exchange, (6) Extending resolution of states by 19F NMR, and (7) Validating 19F NMR spectroscopy by computational methods. Many of these advances are demonstrated through recent 19F NMR studies of a homodimeric enzyme, fluoroacetate dehalogenase.