Geny,
Unfortunately, it is a very common case. In our practice, we have 20-40%
of protein crystals that show this kind of diffraction. We still call
them crystals because they often look beautiful, with nice edges and
planes. My understanding is that the protein molecules are not arranged
orderly enough to show diffraction spots.
It is possible that the crystal was destroyed when the cryo protectant
was added. You may try RT as suggested by Roger (which is the ultimate
test), or just try other methods of cryoprotection and/or cryoprotectants.
For some ideas, i suggest looking into the paper "A review of techniques
for maximizing diffraction from a protein crystal in stilla" by Janet
Newman.
Shooting it a better X-ray source is unlikely to improve the picture
significantly in my opinion. You may simply try increasing the radiation
dose many folds to see if there are diffraction spots at all.
Good luck!
With best regards,
Ivan Shabalin, Ph.D.
Research Scientist,
Department of Molecular Physiology and Biological Physics,
University of Virginia,
1340 Jefferson Park Avenue, Pinn Hall,Room 4223,
Charlottesville, VA 22908
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