Dear Crystallographers, Is there any software in CCP4 which can solve twinned structures? I have several datasets which appear to be tetartohedrally twinned, with possible spacegroup of p31/p32 masquerading as p6222/p6422. I think this is approximately equivalent to 1/8-fold NCS?
The data quality (Rpim, CC1/2) is great and resolution is good at 1.9 Ang, although cut off by detector edge I/sig = ~4. Also, I have a possible SAD dataset with CsI soaked in, measured at CuKa, as well as [way too many] possible MR models (calmodulin, which has a ton of different conformers in the PDB). A major problem is that the cell is pretty big, ~100x100x130, so this means ~8 copies, and with tetartohedral twinning, this is more like 64 monomers I think. I am thinking to try MR-SAD, with some brute-force search-model testing, but I am not sure whether/where this could be done in CCP4. Any suggestions in terms of approaches and/or software? BTW, additive screens to try to grow untwinned crystals did not pan out, and I am pretty much out of protein. I do have a few more nice crystals to play with, but they all have the same morphology. Jacob ******************************************* Jacob Pearson Keller, PhD Looger Lab/HHMI Janelia Research Campus 19700 Helix Dr, Ashburn, VA 20147 email: [email protected] *******************************************
