This may sound like hocus-pocus but it worked for me and may work in other conditions. Try chilling your solution in ice, or prepare your plate with reservoir solution and chill the plate in a tub of ice (surround the plate with ice, do not place the plate on top of the ice). Finishing setting the plate in the ice and place you plate at cooler temperatures such as 4-16 degrees Celcius after set-up.
My progress was substantially improved with this method. I previously had crystals that were small and diffracted anisotropically. I tried other screens to improve crystal size such as additive screen, slowing vapor diffusion using oils and incubating at different temperatures after setting up at room temperature. The crystal grew at a lower concentration of PEG that originally gave precipitation setting up at RT and placing at different incubation temperatures. The end result the crystal increased in size by 5x and gave isotropic diffraction to high-resolution.
Other issues. My protein is very soluble and according to a Pre-Crystallization Screen I should use a protein concentration of 50mg/ml but kept with 20-25mg/ml stock.
Best of luck,
Carlos
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