The EU BIOXHIT standard test crystal – verfiying Se-MAD beamlines

The standard test crystal is designed to provide an automated, fast and robust procedure for identifying potential problems in the complex hardware and software infrastructure of modern protein crystallographic (PX) synchrotron beamlines. The resulting diagnostics should be independent of the data integration software employed (XDS, MOSFLM/SCALA and HKL2000). The cubic form of bovine insulin (space group I213) has proved to be a good first choice for a test crystal, with high reproducibility in crystal growth and freezing, high symmetry for highly redundant data collection, there is an additional need to verify the operation of MAD beamlines, in particular those used for phasing of selenomethionine derivatives. For this purpose we have synthesised an organoselenium compound that crystallises in the suitable space group P41212 and has four selenium atoms in general positions in the asymmetric unit. We have determined precise cell dimensions at various temperatures by X-ray powder diffraction to test the possibility that the cell can be reproduced well enough to provide a precise wavelength calibration for MAD beamlines. We will present our experiences with the new Se-MAD test crystal. We are grateful to the EU for support (LHSG-CT-2003503420) and to the other BIOXHIT partners for the fruitful collaboration. m06.o01