Current macromolecule crystallization screening methods rely on the random testing of crystallization conditions, in the hope that one or more will yield positive results, crystals. Most plate outcomes are either clear or precipitated solutions, in which the results are routinely discarded by the experimenter. However, many of these may in fact be close to crystallization conditions, a fact which is obscured by the nature of the apparent outcome. We are developing a fluorescence-based approach to the determination of crystallization conditions, an approach which can also be used to assess conditions that may be close to those that would give crystals. The method uses measurements of fluorescence anisotropy and intensity. The method was first tested using model proteins, with likely outcomes as determined by fluorescence measurements where the plate data showed either clear or precipitated solutions being subjected to optimization screening. The results showed a ～83% increase in the number of crystallization conditions. The method was then tried as the sole screening method with a number of test proteins. In every case, at least one or more crystallization conditions were found, and it is estimated that ～53% of these would not have been found using a plate screen.
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