Hi Rajakumara, You might try growing the crystals at say 25-30% of your PEG, it might be enough to cryofreeze without additional cryoprotectant if the current mother liquor is not enough. You may also try a serial soak in multiple steps increasing the cryo conc in steps of 3% or so to make the transition gentle. This would be in addition to a 2-step soak as mentioned in Artem's document.
If your diffraction is 4.5A-6.0A due to very small complex crystals and the resolution deterioration is due to x-ray exposure, then you might try seeding to get larger crystals which may be able to tolerate better the exposure to cryoprotectant or x-rays. Although none of these answer your original question, it may help. Best, Debanu. -----Original Message----- From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of Artem Evdokimov Sent: Friday, October 31, 2008 3:58 PM To: [email protected] Subject: Re: [ccp4bb] Cryoprotectant for protein-DNA complex crystal Why soak for a whole minute? A single pass through cryo is usually enough, and that takes a couple of seconds with the right set-up... You could try oil - if you're lucky it solves your issues. Note that not all oils are the same, and many people succeed with blended compositions rather than pure stuff. Finally, you could always try my humble recipe: http://www.xtals.org/crystal_cryo.pdf Good luck, Artem -----Original Message----- From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of E rajakumar Sent: Friday, October 31, 2008 5:22 PM To: [email protected] Subject: [ccp4bb] Cryoprotectant for protein-DNA complex crystal Dear All I am working on protein-DNA complex crystals for data collection. These crystals are grown in 15-20 % of PEG3350 or PEG4000 with pH of 6 to 7. When I soak the crystals more than a minute in the cryo solution (15-20% of Glycerol or ethylenglycol + reservoir) the resolution of diffraction is becoming weak (reducing to 6.0 A from 4.5 A) and also the spots are getting spread (increase in mosaicity). Appears that Glycerol or Ethylene glycol not good cryoprotectants in this case. Is there any study on effect of cryoprotectant on protein-DNA complex crystal and protein-DNA complex dissociation? I also want to know which type (organics, oils, polyols, sugars, polymers.) of cryoprotectant is most preferred in protein-DNA complex crystal. Thanking you in advance Rajakumara E. Rajakumara Postdoctoral Fellow Strcutural Biology Program Memorial Sloan-Kettering Cancer Center New York-10021 NY 001 212 639 7986 (Lab) 001 917 674 6266 (Mobile) Get your new Email address! Grab the Email name you've always wanted before someone else does! http://mail.promotions.yahoo.com/newdomains/aa/
