Hi all, I am having trouble processing synchrotron data with XDS for a large unit cell protein complex (Spacegroup P2, Cell 225 x 256 x 430). My crystals diffract to 3.1 Angstrom, but at this resolution we had significant spatial overlaps. To alleviate this we translated the detector 40 mm in both the x and y directions to achieve higher resolution at a distance of 850mm (on a Pilatus 6M detector), as well as used fine slicing (0.1 degree) for data collection. In addition, our crystals are highly radiation sensitive, so we use vector data collection strategies to expose untouched crystal volumes to the beam to maintain high resolution diffraction. This usually allows us to get 5 frames/spot before moving to a new location due to radiation damage.
However, during my processing with XDS, integration results in very low I/sigma, even at low resolution (ie a value of 1.8), even though we have high intensity reflections that are significantly above the background. Looking at the INTEGRATE.LP and CORRECT.LP, with the refined unit cell parameters the standard deviation of spot pixels is 1.15 and standard deviation of spindle position is 0.20. However, the average three-dimensional profile of strong reflections is usually missing "spots" in 3-4 out of the 9 boxes. A check of the detector origin corresponds with the new beam position (967, 1511) in all the log files. Any help or insight into processing with a translated detector or radiation sensitive crystals would be helpful. We have tried to use HKL and iMosflm, but neither program provides a consistent indexing solution (usually can identify a & b dimensions correctly, but they widely vary in c dimension, sometimes very low (ie 35) or sometimes very high (ie 660). Thanks, Christopher Graduate Student - Department of Structural Biology University of Pittsburgh - School of Medicine 3501 Fifth Avenue BST3, Rm 1043 Pittsburgh, PA 15260 email: [email protected] work: 412-648-8542
