by Peter Nollert
June 18, 2009 17:45
Have you ever heard somebody claim that "Protein Crystallization is half art and half science"? I have, many times. This notion that there's something artistic or even magical about growing protein crystals has always bugged me. A lot actually. In my mind protein crystallization is a science. 100% reproducible science that is, with no dependence on the position of the planets or the person setting up the trial. I suspect that poor control over experimental parameters combined with the critical effects that come into play during nucleation and crystal growth are to blame for difficulties in reproducing crystals. Some people may cope with this issue by labeling crystallization as an 'art'.
A complicating factor has its roots in the many possible crystallization parameters as well as their priorities in crystallization success for one protein target vs. another. For instance, one crystallizer may find that a specific pH and temperature are important to grow crystals of a particular target. A second crystallizer, working on a different protein target, however finds that the purity of the sample prep is the only parameter that determines crystallization success.
Tracking down these main crystallization parameters for each protein we work on is at the heart of what we do when we optimize protein crystallization. Most of the time these are protein purity, concentration and a particular composition of a crystallization cocktail. For others, sometimes seemingly exotic parameters such as precise drop mixing regime, surface/volume drop ratio and the kinetics of evaporation, exposure to light, etc. (long list) are key to reproducibility. Nobody claims that this is a simple task. But it's a science, not an art.
Protein Crystallization Art :) [courtesy of Jeff Christensen]