Hi Sonali, Did you use MBP as your purification tag? That's around 45-50kDa if I remember right.
If not, I've had a decent amount of luck using in situ proteolysis to get crystals of degraded fragments. Try a limited proteolysis first overnight at 4C at varying concentrations of trypsin, see which one gives a nice stable band after overnight. Use that same concentration to add to your protein stock before setting up drops and then try another screen. I always use freshly prepared trypsin stock instead of frozen solutions to make sure that the freeze thaw doesn't reduce activity of the trypsin and that batch to batch is reproducible. Best of luck, Peter
