SR instrumentation for optimized anomalous scattering and high resolution structure studies of proteins and nucleic acids (invited)

Crystal structure solution by anomalous dispersion methods has been greatly facilitated using the rapidly tunable station 9.5 at the Daresbury SRS. Both SIROAS and MAD techniques, with IP data, have been used in the phasing of a brominated nucleotide and a seleno deaminase, respectively. The electron density maps in each case are interpretable. Throughput of projects could be improved upon with a better duty cycle detector. Another category of data collection is that at very high resolution. Detailed structure refinement pushes the limits of resolution and data quality. Station 9.5 has been used to collect high resolution (1.4 Å) native data for the protein concanavalin A. This utilized very short wavelengths (0.7 Å), the image plate, and crystal freezing. A total of 155 407 measurements from two crystals benefited from the on‐line nature of the IP detector device, but a slow and quick pass are required to capture the full dynamic range of the data. There are data seen to 1.2 Å and beyond for a pure Mn substituted form of the protein, but a higher intensity still is required to actually record these data. By comparison, trials at CHESS, on a multipole wiggler (station A1) with a CCD (without image intensifier) system, yield native concanavalin A data to 0.98 Å and beyond. This demonstrates that the combination of yet higher intensity and the ease of use of a CCD offers worthwhile improvements; in this case an increase in the data by a factor of (1.4/0.98)3, thus at least doubling the data to parameter ratio for protein structure model refinement and potentially opening up direct structure determination of proteins of the size of concanavalin A (25 kDa). Finally, possibilities at ESRF and further detector developments, such as mosaic CCDs and scintillator coatings, offer further impetus for the field. These include more intense rapidly tunable beams for anomalous dispersion‐based structure solution and ‘‘ideal’’ higher resolution data collection and reactivity studies. ESRF BL19 is described; facilities on BL19 will include a system for freezing and storing crystals at cryogenic temperatures, so that data can be recorded from the same crystal on different runs. Overall, there have been tremendous strides made in this field in the last 15 years, and yet further improvements are to come

The evolution of synchrotron radiation and the growth of its importance in crystallography

The author's 2011 British Crystallographic Association Lonsdale Lecture included a tribute to Kathleen Lonsdale followed by detailed perspectives relevant to the title, with reference to the Synchrotron Radiation Source (SRS) and European Synchrotron Radiation Facility (ESRF). Detector initiatives have also been very important as have sample freezing cryomethods. The use of on-resonance anomalous scattering, smaller crystals, ultra-high resolution as well as the ability to handle large unit cells and the start of time-resolved structural studies have allowed a major expansion of capabilities. The reintroduction of the Laue method became a significant node point for separate development, and has also found wide application with neutron sources in biological and chemical crystallography. The UK's SRS has now been superseded by Diamond, a new synchrotron radiation source with outstanding capabilities. In Hamburg we now have access to the new ultra-low emittance PETRA III, the ultimate storage ring in effect. The ESRF Upgrade is also recently funded and takes us to sub-micrometre and even nanometre-sized X-ray beams. The very new fourth generation of the X-ray laser gives unprecedented brilliance for working with nanocrystals, and perhaps even smaller samples, such as the single molecule, with coherent X-rays, and at femtosecond time resolution