Hi Theresa, What works well for me, is to use like with like, e.g. to use salts or salt-like cryoprotectants for salt conditions (e.g. malonate, li-sulfate, sucrose/xylitol for ammonium sulfate conditions) and glycerol, low mw PEG etc. for PEG and other alcohol conditions. I have very bad experiences using glycerol with ammonium sulfate conditions. Of course, the pH of the cryo-solution should be the same as of the crystallization conditions to avoid a pH shock.
As mentioned, oils which do not mix at all with the reservoir solution could be tried in both cases. In many cases it helps to increase the salt/peg concentration in the cryoprotectant solution, since under crystallization conditions there is often an equilibrium between protein in solution and in the crystal. By increasing the salt/peg concentration, the protein will no longer be soluble and stay in the crystal. Also often some of the water is pulled from the crystal lattice, resulting in a tighter packing, which is more robust versus soaking and which may diffract better (dehydration effect). Good luck! Herman -----Original Message----- From: CCP4 bulletin board [mailto:[email protected]] On Behalf Of Theresa H. Hsu Sent: Monday, February 06, 2012 11:00 PM To: [email protected] Subject: Re: [ccp4bb] Freezing crystal Hi all Thanks for all the suggestions which I will try soon. How do the crystallization condition (PEG vs. salts like ammonium sulfate) affect the croyprotectant condition? Do factors like presence of low concentration of high molecular weight PEG (> 2000) mean PEG is better? Do buffers and salts in protein also important? Trying to rationalize it :) Theresa
