This special Physics department colloquium is scheduled for Monday 11/23/15 at 3:30 PM in the Kenwood Interdisciplinary Research Complex (KIRC) Room KEN 1150. Coffee and cookies will be available in KEN 3118 (third floor kitchenette located next to the elevators) at 3:00 PM. Anyone is welcome.

Time-Resolved, Near Atomic Resolution Structural Studies at the Free Electron Laser
Jason Tenboer, PhD Candidate/UWM Dept. of Physics

Time-resolved serial femtosecond crystallography (TR-SFX) employs X-Ray free electron lasers (XFELs) to provide X-ray pulses of femtosecond (fs) duration with 1012 photons per pulse. For structure determination, protein crystals on the micrometer length scale (microcrystals) are injected into the X-ray beam and the resulting diffraction patterns are recorded on fast-readout pixel detectors. Although these intense pulses deposit enough energy to ultimately destroy the protein, the processes that lead to diffraction occur before the crystal is destroyed. This diffraction-before-destruction principle overcomes radiation damage since each diffraction image is obtained from a fresh crystal. Therefore, reversible and non-reversible reactions may be studied in the same fashion.

With an initial experiment performed at the Linac Coherent Light Source (LCLS) we demonstrated for the first time that near atomic resolution TR-SFX is possible using an XFEL. Continuing on this work, we have now determined previously uncharacterized structures of the photoactive yellow protein photocycle. This fs time-resolved study demonstrates the full capability and vision of XFELs with respect to photoactive proteins. In addition to studying photo-initiated reactions, XFELs offer the unique opportunity to explore irreversible enzymatic reactions by the mix-and-inject technique. In this method, microcrystals are mixed with a substrate and the following reaction is probed by the fs X-ray pulses in a time-resolved fashion. One of the primary missions of an XFEL is to routinely record a complete time-series at atomic resolution and near physiological temperature of these non-reversible fast enzymatic reactions. This capability would catalyze the rapid advancement of structure-based drug designs.