MX beamlines are extremely powerful instruments for solving the structure of proteins. There are nearly 100 operational Macromolecular Crystallography (MX) beamlines around the world, and being able to accurately calibrate them is vital to ensuring the accuracy of the data they collect. Scientists from Diamond have shown that an unusual calibration standard – beeswax – may be able to help this happen. This work has been published in the Journal of Synchrotron Radiation.
Although X-ray intensity calibration standards for synchrotron beamlines do exist, none of these are entirely suitable for MX beamlines. Hen egg-white lysozyme is quite widely used, as it is easy to crystallise and the size and shape of crystals can be controlled to some extent, and suitable crystals can be grown over 3 – 4 days. However, lysozyme is susceptible to radiation damage, and although the crystal can be stabilised, the stabilisation process leads to variable results.
MX samples are typically protein assemblies and are polymeric crystals with unit cell dimensions ranging from tens to hundreds of Ångstroms. For a standard to be viable, it needs to have properties similar to MX samples. The standard also needs to be readily available, high quality, stable, durable and provide repeatable results. In addition, because the source, optics and detectors are important factors, the morphology needs to be controllable, and single crystal samples are not ideal.
Waxes are easily moulded to known shapes and they have similar physical properties to MX samples. As such, waxes are good candidates for a calibration standard. The study examined thin discs of commercially available waxes using beamlines I11 (Powder Diffraction) and I04 (Macromolecular Crystallography).
"Providing MX practitioners with a calibrated intensity standard analogous to MX samples will act as a quantitative benchmark and make it straightforward to compare the quality of the experimental setup between different sources."
Jose Brandao-Neto, Diamond Light Source
Characterization of wax as a potential diffraction intensity standard for macromolecular crystallography beamlines, Brandao-Neto J, Thompson SP, Lennie AR, Ferreira FF, Tang CC., J Synchrotron Radiation, 2010 Jan;17 (Pt 1):53-60
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