Hello folks, I have crystals for a protein which form in 0.1 M MES pH 6-6.75, 10% dioxane and 1.6-2 M Ammonium sulphate. Based on little experience I have finding the right cryoprotection for salt based conditions; I have tried glycerol (15-25%), Ethylene glycol (20-25%), DMSO (15-20%) and increasing ammonium sulphate concentration in presence of 5-10% glycerol. The crystals disintegrate in any kind of PEG based cryo. I made all these solutions in the mother liquor and tested if they freeze clearly before using them. However when I loop the crystals and try to soak them in these cryo- mother liquor, a lot of salt crystals suddenly form around the protein crystal and I see diffraction only from these salt crystals. The best I have been able to get so far is ~ 9Å diffraction (Home-source) with DMSO as the cryoprotectant.
I have also tried using 1 M sodium malonate as the cryoprotectant but my crystals are not too stable in this mother liquor probably because I had to lower the ammonium sulphate by ~ 7-10% to make the drop not form salt crystals instantly when exposed to air. Other than trying to make the crystals more cryo-ready by finding other hits or may be growing the same crystals with some cryoprotectant, I was wondering if any of you have ideas based on your experience or suggestions in case I am doing everything wrong in the first place. Thanks for all the help, Mahesh
