Dear CCP4 Contributors, I have a bit of a mystery:
Two co-crystals that I picked up from the same grid tray (the two conditions vary slightly in %PEG and [salt], both indexed as P1 (apo structure normally crystallizes in P3221). One dataset was indexed, integrated and scaled with HKL2000. The other was processed with MOSFILM (could not process in HKL2000). Downstream processing for both sets was done exactly the same in PHENIX. Though both asymmetric units contain two complete tetramers, the interesting thing is that the configuration of monomers is different between the solutions. One contains one complete tetramer, one trimer (with a void where the fourth monomer would be), and one monomer on off on its own. The asymmetric unit of the other dataset solution also contains a complete tetramer, but then has two dimers. Close analysis of contacts between symmetrically related molecules reveals that the crystal packing is exactly the same between the two solutions from the two datasets. Also, the Rwork and Rfree for both models are 0.18 and 0.20. Other quality indices are also comparable between the two sets. Here's my question: Does this phenomenon reveal anything important, or is this type of thing just seen sometimes with P1 solutions from crystals of the same protein and condition (more or less). I hope I have been clear. Thanks! Gabriel
