A solution could be to control the solubility of your protein in different pH and salts (you can also add some additives) by using the Thermal Shift Assay. You may find a better buffer in which to concentrate your protein.
If you think that the reason of the low diffraction is the quality of your crystals try the suggestion of Eric, but if you think that is due to the small size of the crystals, you can also try to make drops of 3µl (2µl of protein and 1µl of the well) or to feed your crystals during the growing (i.e. adding 0.5µl of protein solution to your drop after when you see that the crystals stop to grow), or to do seeding like Eric suggests, but in big drops (5µl in hanging or more in sitting drop) and with serial dilutions of the seeds. Good luck... Michel. Dear All: > We have been trying to crystallize a protein which is large - > 100 kDa. > This is soluble but the best we can get is about 1 mg/mL. > It did crystallize but did not diffract well. Efforts to increase the > concentration has been unsuccessful. I am wondering whether there are > methods that others use to increase the concentration other that using > amicon columns. > Any help will be appreciated. > Thanks > Subbu >
