Hi Lucas, The funky diffraction pattern is most likely due to a cracked crystal, resulting in a mixture of slightly differently aligned diffraction patterns. Were the cracks there before you added the cryprotectant? If not, the cryoprotectant is definitively to blame. As has mentioned before, you have to take a shot at room temperature without any cryoprotectant added, to make sure the bad quality is not due to the cryoprotectant. Mitegen sells plastic capillaries, which you can slide over your loop to prevent the crystal from drying out.
Good luck! Herman -----Original Message----- From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Yi-Liang Liu Sent: Thursday, August 02, 2012 4:15 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Enhancing Crystal Quality Hi, Thanks for the kindly answers from everyone. I actually haven't tried different cryoprotectants. I might will give a try next time. I usually only use mother liquor+30% PEG400. It is noticeable that it has some "patterns (cracks (?))" on the crystal. However, it didn't form icy rings or etc. The diffraction pattern looks funky too. It looks like it is twin and the diffraction spot has tails. Does this indicate the cryoprotectant problem? Lucas On Aug 1, 2012, at 2:11 PM, Antony Oliver wrote: > 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" <yiliang...@gmail.com> 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
