Figure 1. Biophysical methods to study protein structure and dynamics.

Whereas x-ray crystallography is the most robust method to determine high resolution structures of small and large proteins, cryoelectron microscopy is best suited for large proteins and protein complexes. Despite its utility to investigate dynamic properties, current molecular size constraints limit the applicability of liquid state NMR to <50,000 MW. In contrast, EPR and fluorescence spectroscopies can interrogate dynamic processes regardless of size or complexity. The application of these probe-based methods to proteins of known structure amplifies the interpretation of data toward understanding mechanism.