Abstract
X-rays play a pivotal role in macromolecular crystallography, being the probe used to solve protein crystal structures. The scope of the X-ray crystallography method for structure elucidation and refinement has been transformed by synchrotron-radiation (SR) sources; a particular development has been that larger molecular weight structures and complexes have become amenable to study. Small crystals have also become less restricting and are now used routinely. The finding of isomorphous derivatives to solve the crystallographic phase problem has been circumvented in a majority of cases via optimized anomalous scattering; of especial note being the coupling of the use of tunable SR with the harnessing of novel microbiological production of selenomethionine protein variants. Much higher diffraction resolution studies are also now possible. This chapter describes all these scientific applications of SR. It starts with the physics of SR, including storage-ring insertion devices, and the beam characteristics that can be delivered to the sample. The evolution of the machines and detectors has been substantial; small SR-machine emittance, microfocus beams and almost instantly digitized diffraction images make for near-revolutionary changes of capability. Monochromatic beams are also now fully wavelength tunable, providing narrow spectral spread and yet high intensity at the sample. White-beam options are also harnessed for ultra-short single-bunch time-resolution Laue diffraction; sub-nanosecond time resolutions are viable for structure–function studies, which are described in the companion Chapter 8.2 by K. Moffat. New X-ray free electron laser (XFEL) sources are coming online with even higher single pulse fluxes. Upgrades to the third-generation synchrotron-radiation sources such as at the ESRF are approved and will provide nanofocus X-ray beams (extending down to 10 nm). Keywords: Laue diffraction; curved single-crystal monochromators; double-crystal monochromators; insertion devices; MAD; monochromators; multiwavelength anomalous diffraction; rocking width; structural genomics; synchrotron radiation; time-resolved studies; X-ray free electron laser; X-ray sources
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