Hi Frank,
unfortunately it is very common with membrane protein crystals to get "stuck" with diffraction quality around 20A.
From what you describe you could consider the following:
a) revise the detergent you solubilize your MP with (e.g. use OG instead of DDM), and consider to change to another (shorter) detergent that might allow tighter crystal packing
b) engineer your MP,mutate charged residues to alanine (check function!)
c) try homolog protein
d) try to crystallize in lipid cubic phase
Best of luck!
Susanne
On Oct 23, 2013, at 9:22 AM, crystalboy wrote:
Hi CCP4BB Forks,
In recently I got a membrane protein crystal in the quite normal
membrane protein crystallization conditions as other persons reported,
like PEG400 16-19%, pH 6.0-7.5, with 50 mM MgCl2 (in my case) by using
sitting drop method. These crystals are around 50-100 uM. They look
like trapezoid crystal. My problem is all of my crystals have not
diffraction in home source X-ray and just poor diffraction at
Synchrotron (lower than 20 A). My crystals like to appear on the
surface of the drop. Look like my crystals are quite light. I had
tried to use a needle to touch them. Unlike other protein crystal, my
crystal looks like quite "soft". When I touch it, it didn't crack, but
was bend or mashed. I had tried to do additive screen and detergent
screen. It seems they are not useful.
Do anyone have good ideas to optimization these crystals? Thanks for
your suggestions.
Frank
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Dr. Susanne Ressl
Otto Hahn Fellow of the Max-Planck Society
Stanford University
School of Medicine
James H. Clark Center
318 Campus Drive, Room E300
Stanford, CA 94305-5432
Phone: +1-650-736-1715