Dear CCP4BB members, I have solved a protein-drug complex structure in P21212 space group. In this structure, the drug molecule is falling on the two-fold symmetry axis having averaged electron density with 0.5 occupancy. We tried a lot to crystallize this protein-drug complex in different space group but no success so far. I have tried to solve the same data in space group P1 (statistics are fine as I have collected data for 360 degree). The map looks even better with one conformation for a drug. Interestingly, then I reprocessed the same data using imosflm in P21 space group which have penalty 1 compared to 4 for P21212. The structure in P21 is also refining well (with one conformation of the drug compound without symmetry axis at the ligand position). The question is , is it a good practice to solve this structure in P1 and P21 even if the data has higher symmetry?
Secondly, I have been advised that I have to be careful to refine structure in P1 as there will be problem regarding observation/parameter ratio if I add too many water molecules. What will be the case if the electron density present for water molecules? I can put restrains to protein structure but I am just curious to know one restrain equals how many observations. I look forward to hear your suggestions. Kind regards, Mohinder Pal
