PICOSECOND TIME-RESOLVED LAUE CRYSTALLOGRAPHY

University Of Chicago, Chicago IL

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We aim to employ the technique of picosecond time-resolved Laue crystallography to study biophysical processes in proteins. Specifically we will use intense short-duration laser pulses to trigger a structural change in a protein crystal and will probe its structural evolution with single X-ray pulses isolated from the synchrotron pulse train using a sequence of X-ray shutters. By acquiring diffraction data at a well-defined instant in time after laser photolysis we can construct a snapshot of the proteins structure with time resolution limited only by the duration of the X-ray pulse which is of the order of 100 ps. We aim to address numerous biophysical questions including the functional role of highly conserved residues in proteins pathways for ligand migration to and from the proteins active site and the correlated structural changes that mediate or control allosteric regulation. To obtain the highest quality data possible we will focus initially on protein systems whose structural changes are reversible. Ligand-binding heme proteins including myoglobin and hemoglobin are ideal model systems for these biophysical investigations. When CO is used as a surrogate for O2 the ligand can be photodissociated from the heme with high quantum efficiency thereby triggering a sequence of events that can be studies structurally. Because the dissociated ligands rebind to the heme bimolecularly on the ms time scale the structure returns to its starting state and the process can be repeated thousands of times. Thus these model systems are ideal for pursuing these biophysical studies.