Hello all,
I am working on the structure of a small protein in space group P212121. The protein is monomeric in solution based on gel filtration analysis. The Matthews Coefficeint program indicates that 9-10 molecules per asymmetric unit results in ~50% solvent content, while 1 molecule per asymmetric unit results in ~95% solvent. I tried molecular replacement with a search model which is essentially identical in sequence to my protein, and searched for 9 or 10 molecules/asu. Using MolRep with 9 or 10 molecules/asu, I get poor contrast scores around 1-1.5. However, when using Phaser, I get a solution with one molecules/asu. Likewise, when I went back and tried MolRep with 1 molecule/asu, I got a contrast score of 3.12. This model still has some issues, but looks more correct compaired to models created with 9 or 10 molecules/asu. It seems highly unlikely that a crystal would contain 95% solvent, but is there any possiblility that this could be the case? Assuming that the Matthews coefficient is correct, does anyone have an idea why MR seems to work better for 1 molecule/asu with 95% solvent content compared to 9-10 molecules with 50% solvent content? Alternatively, is there any reason why the Matthews coefficient could be calculating incorrectly? Any suggestions would be helpful. Thanks, Matt
