A first concern with that extreme anisotropy is at the integration and scaling stages. Large swaths of your detector are empty of reflections, but they will still bias the way reference profiles are calculated at integration; while the lots of reflections with intensities around 0 (but with significant sigmas) will bias the statistics for scaling the real reflections (real as in having intensity). You are better off excluding all the parts of the detector that do not contain significant intensities (and taking a hit in completeness) than trying to correct for all the "0" intensities. While the optimum would be to limit integration to an elliptical area of the detector containing the significant intensities, I am not aware of any program that can do this elegantly. In my experience, the strong data almost always end in the "horizontal direction" of the detector. And in many cases, the significant area while really elliptical, can be approximated to a rectangle, with the long edges horizontal. In that case, a simple trick is to use the "excluded" areas in the integration programs to limit integration to your rectangle. In Denzo I usually did this by playing with the detector distance, so that the diffraction ends at the edges of the detector, effectively setting the 2 short sides of our rectangle, and set the long edges of the rectangle with the excluded rectangle and excluded circle options (a circle of very large radius centered way out of the detector can be an excellent approximation to a straight line for cutting purposes). I am sure most programs will allow for equivalent ways of limiting integration to a rectangle. Once you have an mtz file with intensities, the UCLA anisotropy correction server can be a great help too.
"Marie Lacroix" <lacroix.ma...@rocketmail.com> wrote: > > > > > Hi, > > I also have a question concerning anisotropic data. Collected a data set and the > best crystal gave highly anisotropic diffraction patterns ( 3.7 A - 5.8 A). So > my first question is how to handle these data. I got only experience with > "normal data" using the ccp4 suite. Are there any program specially for these > kind of data? There are? > The second question is how anisotropic data occur? The protein I work with has a > tetragonal sg with a=b= 86.0 and an extremely long c axis of 651 A. Secondary > Structure prediction suggest a lot of beta strands. How can I explain the > anisotropy (for my own interest and my thesis)? > Thank you very much. > > Marie > > > -- *************************** Jose Antonio Cuesta-Seijo Biophysical Chemistry Group Department of Chemistry University of Copenhagen Tlf: +45-35320261 Universitetsparken 5 DK-2100 Copenhagen, Denmark ***************************
