Crystal growth: Tips and Tricks
I tried Hampton Screen I & II with my protein and have no crystals. What can I do?
1. There are other screens. While it is proably true that when proteins do crystalize, they in many cases produce hits from Hampton screens I or II, we are dealing here with exception to that rule. Lists of screens are available from manufacturer websites:
2. Vary protein concentration. This is rather obvious suggestion when all your drops are clear or all have precipitate, in which case your overall concentration is too low (too high). More elaborate approach is to modify concentrations based on the results of your first screen, i.e. double it for the conditions which produced clear drops and cut it in half for those which produced precipiate. To avoid concentrating/diluting protein, you can simply try to mix your original protein stock with reservoir solutions in different proportions. For instance, mixing 2ul of protein with 1ul of reservoir solution is (to some degree) equivalent of doubling protein concentration.
3. Set your screens at different temperature. 25 and 4 degrees are the most popular options. If you completely lost hope for your original screens, just transfer them to the cold room. Protein solubility will change and you may get crystals.
4. Add a purification step. Purity can be critical to protein crystallization and the purity judged from SDS-PAGE or even gel filtration can be misleading.