What is it about?
The pH is one of the most important parts of crystallising proteins. It is normally recorded as the pH of the buffer; however, the actual pH can be different to that of buffer. In the future, it is possible to record a more accurate measure of the pH by using a pH indicator. For historical crystallisation experiments it is impossible to measure the pH. It is, however, possible to predict the pH based on the contents of the solution. Using either a neural network (machine-learning) or a regression-model an estimate of the true pH can be found, where the inputs to the model are the concentrations of the chemicals in the solution and the output is the pH.
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Why is it important?
Protein crystallisation assists in the development of drugs. It is, however, very difficult to get proteins to crystallise. Any method of improving the number of proteins crystallised could improve the number of protein structures found. This particular method is important as there is lots of protein crystallisation data and lots of it has the pH recorded incorrectly. Therefore, any conclusions based on this old inaccurate pH are likely to be misleading. The new method of predicting pH will allow for more accurate conclusions to be drawn. Exploring the link between pI and pH will allow for crystallisation solutions to be customised for specific proteins.
Perspectives
The real pH and the recorded pH can be very different, up to three units. Thankfully, a highly accurate model can be created for chemical solutions with a buffer to predict the true pH. We did this by measuring the pH of 1000s of solutions, and then comparing it to a predicted pH obtained from out model. The link between pI and pH has been fiercely contested in the past decade with neither side coming out on top. Here, we attempted to add clarity to the situation by investigating the link further and showing there does appear to be a link.
Dr Jobie Samuel Kirkwood
University of York
Read the Original
This page is a summary of: Using isoelectric point to determine the pH for initial protein crystallization trials, Bioinformatics, January 2015, Oxford University Press (OUP),
DOI: 10.1093/bioinformatics/btv011.
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