Temperature-Jump Solution X-ray Scattering Reveals Distinct Motions in a Dynamic Enzyme

Correlated motions of proteins are critical to function, but these features are difficult to resolve using traditional structure determination techniques. Time-resolved X-ray methods hold promise for addressing this challenge but have relied on the exploitation of exotic protein photoactivity, and are therefore not generalizable. Temperature-jumps (T-jumps), through thermal excitation of the solvent, have been utilized to study protein dynamics using spectroscopic techniques, but their implementation in X-ray scattering experiments has been limited. Here, we perform T-jump small- and wide-angle X-ray scattering (SAXS/WAXS) measurements on a dynamic enzyme, cyclophilin A (CypA), demonstrating that these experiments are able to capture functional intramolecular protein dynamics on the microsecond timescale. We show that CypA displays rich dynamics following a T-jump, and use the resulting time-resolved signal to assess the kinetics of conformational changes. Two relaxation processes are resolved, a fast process is related to surface loop motions and slower process is related to motions in the core of the protein that are critical for catalytic turnover.