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Fast SAD Phasing with Sulfur

AppNote PX014: Protein single crystal sulfur SAD phasing using X-ray diffraction

Background

The XtaLAB MM007-HF is Rigaku Oxford Diffraction's most popular single crystal diffractometer ideal for small molecule and/or macromolecular X-ray crystallography in the home laboratory. The system uses a MicroMax-007 HF source, the gold standard in high uptime/low maintenance microfocus, rotating anode generators. The high flux and brilliance provided by the MicroMax-007 HF, in combination with a VariMax confocal optic and a Dectris PILATUS 3R 200K hybrid photon counting (HPC) detector, enable rapid data collection and accurate measurements. In fact, even the weak anomalous signal from the sulfur atoms residing in the methionine and cysteine residues of a protein chain can be measured and used to solve a structure by single wavelength anomalous dispersion (SAD) in minutes. Here, we used the XtaLAB MM007-HF to collect data on a crystal of Thaumatococcus daniellii thaumatin in the absence of a strong anomalous scatterer. A total of 668 degrees of diffraction data were recorded in 11 minutes, and the structure was solved by S-SAD phasing.

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