Using isoelectric point to determine the pH for initial protein crystallisation trials

The identification of suitable conditions for crystallization is a rate-limiting step in protein structure determination. The pH of an experiment is an important parameter and has the potential to be used in data-mining studies to help reduce the number of crystallisation trials required. However, the pH is usually recorded as that of the buffer solution, which can be highly inaccurate. Results: Here we show that a better estimate of the true pH can be predicted by considering not only the buffer pH but also any other chemicals in the crystallisation solution. We use these more accurate pH values to investigate the disputed relationship between the pI of a protein and the pH at which it crystallises.