The problem you're having is a very common one, unfortunately. There are about 10,000 things you can try to improve diffraction....generally going from low to "solvable" resolution is very, very hard. I would say the two most important ones are (i) to vary the detergent and (ii) to go to another homolog if (i) doesn't work. You don't mention which detergent you're using (DDM?), but the best chance of success would be to try harsher detergents, ie those that form small micelles (shorter chain maltosides, b-OG, LDAO etc). Give bicelles a try too, and LCP if you know someone with an LCP robot. If your protein is stable only in DDM you're out of luck and the best thing would be to look for an ortholog that is more stable.
Good luck, Bert ________________________________________ From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of crystalboy [yyb...@gmail.com] Sent: Wednesday, October 23, 2013 5:22 PM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] membrane protein optimization 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
