Further dehydration did not change diffraction quality, until a drastic loss of diffraction occurred at 85% relative humidity. The diffraction could be recovered when the humidity was increased in several steps from 85 to 90% and persisted up to a relative humidity of 97%. The main improvement during the dehydration steps was the appearance of diffraction spots smeared into lines up to a resolution of approximately 8 Å. Rehydration of the crystals tended to resolve spots, but at the

expense of resolution. Protein crystallization itself is an efficient protein purification technique, and therefore we expected that crystal quality might be improved by recrystallization. selleck products Unfortunately, initial attempts with CP43 crystals were unsuccessful, because the protein precipitated when crystals were dissolved in buffer B. Acknowledgments We are grateful to R. Kiefersauer and S. Krapp at PROTEROS, Martinsried, for the help with the initial crystal dehydration experiments. M. Nowotny kindly helped to test some crystals at synchrotron beamlines. G. Bourenkov advised on the interpretation of diffraction patterns of the CP43 crystals. H. Czapinska contributed with stimulating discussions and critically read the manuscript. We thank the staff at ESRF, Diamond, DESY

and BESSY for the availability of beamtime for test exposures. This work was done with financial support from Marie Curie Host Fellowship “Transfer of Knowledge” (MTKD-CT-2006-042486) and MNiSW decision 151/6.PR UE/2007/7. Open Access This article is distributed Sotrastaurin under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. References Adir N (1999) Crystallization of the oxygen-evolving reaction centre of photosystem II in nine different detergent mixtures. Acta Cryst D55:891–894 Barber J, Nield J, Morris EP, Zheleva

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