Synchrotron X-ray crystallography techniques: time-resolved aspects of data collection

Abstract

Synchrotron X-radiation (SR) is intense, polychromatic and collimated. These properties are exploited routinely now to measure data at high resolution from proteins or from large unit cells (e.g. viruses), particularly using a monochromatized short wavelength beam. The time needed to measure protein crystal data-sets (in rotation geometry) can be quick (hours or minutes) compared with laboratory sources (weeks or days). Even so, more rapid data collection is of interest for timeresolved macromolecular crystallography. White beam : stationary crystal (Laue) geometry at SR sources offers shorter exposure times (seconds and less with film). Laue data-sets can be sensitive to subtle structural differences. Technical challenges still presented by SR Laue patterns include the energy overlap of low-resolution data and the spatial overlap of spots, both of which affect the completeness of data-sets. Some energy deconvolution is already possible by the use of multiple films. The spatial overlap problem can be alleviated by the use of three-dimensional detectors, such as a ‘toast-rack’ of plates. Monitoring of a crystalline process, via the Laue pattern, requires time slicing detector systems (e.g. based on CCDS) to be developed.