Hi Frank,
The previous suggestions are great. In my case, I had soft crystals (bend from 180° to ~130-140°) in the loop using the LCP but they still diffracted. There are a lot of "heroic stories" on how some people solved a structure, you should just try as many ways as possible (do not only rely for a long time on only one condition or construct), and remember "methods" are just methods (i.e., there are hundreds of LCP robots in the world..). Protein engineering, homologs (maybe hyperthermophiles).. stabilization.. are great ways.
Recently I had tested various crystals grown by vapor diffusion for a protein purified in different ways/detergents, so obtaining crystals is very common, but it's just the start. I also had crystals using bicelles but saw huge spots to 2 A (no patterns.. rather looked like detergent/lipid).
Good luck
toufic el arnaout
________________________________________
From: CCP4 bulletin board [[log in to unmask]] on behalf of crystalboy [[log in to unmask]]
Sent: Wednesday, October 23, 2013 11:22 AM
To: [log in to unmask]
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
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