Dear Kevin, It could also be that you have a particular nasty combination of tNCS and twinning. Given your packing problems in the ab plane, this would mean that your 2-fold parallel to c is generated by twinning and that probably one of the 21 axes is generated by twinning as well.
With some very clever thinking, you might be able to figure out what the appropriate lower-symmetry space group would be, but I would follow the advice of John Helliwell: reprocess the data in P1 and run molecular replacement in P1. MR is usually quite insensitive to twinning and will produce two solutions with equal probability. Once you have the packing, you can try to figure out how to best describe this packing in terms of a space group with tNCS. If your data collection statistics do not suggest any twinning, you may have some other pathology like statistical disorder. In any case, with this space group problem, you have great opportunity to learn a lot about crystallography! Best, Herman Von: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] Im Auftrag von Kevin Jude Gesendet: Freitag, 31. Mai 2019 22:09 An: CCP4BB@JISCMAIL.AC.UK Betreff: [EXTERNAL] [ccp4bb] tNCS incompatible with cell dimensions EXTERNAL : Real sender is owner-ccp...@jiscmail.ac.uk Hello community, I wonder if I could solicit advice about a problematic dataset. I plan to solve the structure by molecular replacement and expect that the protein is relatively compact, ie not elongated. SAXS data supports this expectation. The crystals diffract to 2.6 Å resolution and appear to be in P 21 21 2 with a = 49, b = 67, c = 94, which should fit <=2 molecules in the ASU with 40% solvent. The native Patterson shows a large peak (12 sigma) suggesting a tNCS vector of {0.5, 0.5, 0}. If you're sharper than me, you may have already spotted the problem - c is the long axis of the unit cell, but tNCS constrains the proteins to a plane parallel to the a,b plane. Indeed, molecular replacement attempts using Phaser will not give a solution in any orthorhombic space group unless I turn off packing, and then I get large overlaps in the a,b plane and huge gaps along c. Since I believe that my model is good (or at least the correct shape, based on SAXS), I wonder if I'm misinterpreting my crystallographic data. Any insights into how to approach this problem would be much appreciated. -- Kevin Jude, PhD Structural Biology Research Specialist, Garcia Lab Howard Hughes Medical Institute Stanford University School of Medicine Beckman B177, 279 Campus Drive, Stanford CA 94305 Phone: (650) 723-6431<tel:%28650%29%20723-6431> ________________________________ To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.jiscmail.ac.uk_cgi-2Dbin_webadmin-3FSUBED1-3DCCP4BB-26A-3D1&d=DwMFaQ&c=Dbf9zoswcQ-CRvvI7VX5j3HvibIuT3ZiarcKl5qtMPo&r=HK-CY_tL8CLLA93vdywyu3qI70R4H8oHzZyRHMQu1AQ&m=vmdYqzxEW-6CZ0aPOoLf1mJIITHuMZuwsCDSG0prB_I&s=GAjinhLyYSX2xoEKpyZ-6-cQSmCdznPFaVDjJyzMAE0&e=> ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1
