We have developed time-resolved X-ray methods capable of visualizing structural changes in proteins on time scales as short as ~100 ps. This infrastructure was first developed on the ID09B time-resolved beamline at the ESRF, and more recently on the ID14B BioCARS beamline at the APS. Briefly, a picosecond laser pulse photoexcites a protein and triggers a structural change. A suitably delayed picosecond X-ray pulse passes through the protein and its scattering pattern is imaged on a 2D detector. When the sample is a protein crystal, this �pump-probe� approach recovers time-resolved diffraction �snapshots� whose corresponding electron density maps can be stitched together into movies that unveil the correlated motions that arise from the photoexcitation event. When the sample is a protein solution, time-resolved small- and wide-angle X-ray scattering (SAXS/WAXS) patterns are recorded, whose radial intensity distribution is sensitive to changes in the size, shape, and structure of the protein. Importantly, scattering studies of proteins in solution unveil structural dynamics without the constraints imposed by crystal contacts; thus, these scattering �fingerprints� complement results obtained from diffraction studies. Together, these studies provide detailed information into the relations between protein structure, dynamics, and function. Recent studies of photoactive yellow protein will be presented. This research was supported in part by the Intramural Research Program of the NIH, NIDDK.

Picosecond time-resolved X-ray studies of photactive yellow protein

244th National Meeting (2012)

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