Have you tried different cryoprotectants? Can make a huge difference. Also, have you shot an xtal at room temp - to see what the intrinsic diffraction limit is? Additive screens? If all else fails you may well need to explore a different expression construct.
Tony.
Sent from my iPhone
On 1 Aug 2012, at 19:52, "Yi-Liang Liu" <[log in to unmask]> wrote:
> Hi CCP4BBers,
>
> I have a protein crystallized with 0.2mM Mg acetate and PEG 8000 or 0.1mM cacodylate, pH 6.5, 0.2 Mg acetate, PEG 3350. Both of the conditions gave triangle pyramid like crystals. I brought the crystals to synchrotron using 30% PEG 400 as cryoprotactant, the resolution was only be able to reach 4A or worse. I have tried changing pH and concentrations of PEG, PEG types. I found out this crystal only grew between pH 6.5~7.5 and PEG types did not change the result of diffraction dramatically. I have also tried the seeding (break it down and reseed in the same condition. Maybe I did it wrong?). It gave me the similar results, not improving. Is there any simple way of improving it before jumping into reengineering the protein.
>
> Thanks,
>
> Lucas
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