What is the best concentration of protein to use for an initial screen of crystallization conditions?
The majority of people polled work in the 5 to 10 mg/ml range of protein concentration. (Bob Cudney) A continually updated survey of the literature shows an average protein concentration of 14.5 mg/ml. (Patrick Shaw Stewart) This is going to be technique dependent. Batch experiments will require a higher protein concentration than vapor diffusion experiments. Looking at 800 experiments in the literature 4 were set up at < 2mg/ml and 4 were set up at >300mg/ml. The majority are set up in between that wide range of concentrations. Add a larger volume of protein than crystallization cocktail to your experiment drop to increase the amount of protein in the experiment. (Shane Atwell) Commercial screens seem to be targeted to a protein concentration of 10 mg/ml. Wizard screens seem to work best at a slightly higher protein concentration than the other screens. The Hampton pre-crystallization test (PCT) was reported to work well.
