Dear Zhao -
This is a salt crystal. You do have spots, even if some of them are
streaky, and if you look carefully, you'll see that some of them are
arranged in regular lines. However, there are very few, and no spots
below about 6 A. This indicates a very small unit cell, with dimensions
probably < 10 A, which can only be a salt or other small molecule crystal.
The usual check for this is to rotate your crystal by 5-10 degrees,
instead of the usual 0.5 - 1 degree. This will put more spots on the
image, and it should become evident what you are dealing with.
Consider all of the components of your protein buffer + crystallization
solution - some combination (e.g. calcium plus phosphate) is most likely
not very soluble, and can come out of solution.
Hope that helps,
Matt
PS. Those crystal dyes are notorious for giving false positives. I
never use them to check if a crystal is protein.
On 7/23/12 4:52 PM, gengxiang zhao wrote:
Dear CCP4BB,
I have a question about my current diffraction map for one of crystals
which can be found in the attachment. Basically, the crystals were
dyed to initially testify that it belongs to protein. But from this
diffraction, even in the low diffract angle, no diffraction spots
there----meaning-----this is not a protein crystal?
Any experienced idea/questions welcomed to discuss here.
Zhao,
--
Matthew Franklin, Ph. D.
Senior Scientist
New York Structural Biology Center
89 Convent Avenue, New York, NY 10027
(212) 939-0660 ext. 9374
