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Hi, I am trying to crystallize a c. 200 kDa pentameric membrane protein of 40 kDa subunits, purified in LDAO detergent. It is soluble (not pelleted after half hour spin at 100,00G) at 10 mg/mL. However, using the Molecular dimensions Memsys/start screen, it immediately precipitates on mixing with the precipitants in each well, even when the protein is diluted down to 2 mg/mL and the precipitant diluted two fold. Now I'm hesitating about the best thing to do - try and do all screens at 2 mg/mL protein concentration or less (which, at 10 uM, seems unusually low from what I've read) or to stick with more typical protein concentrations for protein concentration (i.e. 50 uM as recommended in the MemSys/start instructions, which is 10 mg/mL for my protein) and just dilute the precipitant as much as possible. Any suggestions welcome! Rob.
