Smart hydrogel crystal gardensGrowing good-quality single crystals of proteins for high resolution X-ray diffraction relies on the use of a diverse range of materials as nucleating agents. Smart hydrogels, in the form of molecularly imprinted polymers, may provide a general solution.
Michael J. WhitcombeProteomics and genomic studies are set to provide a much deeper understanding of the structure and function of living organisms at the molecular level by gaining insight into the role of newly discovered proteins in the cell. As more and more proteins are identified, it becomes a pressing matter to determine their 3-dimensional structures -particularly through the use of high-resolution X-ray diffraction studies. Proteins are, however, notoriously difficult to crystallise, especially in high enough quality to obtain good X-ray diffraction patterns.Crystallographers know that the best method to produce good crystals is to grow them under metastable conditions -conditions under which nucleation will not spontaneously occur.The trick, therefore, is to find a substance that acts as a nucleation centre, kicking-off crystal growth which can then proceed at a controlled rate. The ideal candidate would be a small crystal of the protein in question, but for most proteins this represents the classic chickenand-egg situation! Instead, a variety of materials -including objects such as hair, minerals, charged surfaces, thin films and porous solids -are used in the hope that they will provide the vital nucleation step. Now, writing in the Proceedings of the National Academy of Sciences USA, Naomi Chayen and colleagues have shown 1 that help may be at hand in the shape of molecularly imprinted polymers (MIPs).MIPs are cross-linked materials formed in the presence of a molecular template. Interactions between the template and the functional groups of the monomers present in the polymerization mixture ensure that affinity sites -complementary in size and functionality to the templating agent -are formed (Fig. 1a) in the imprinted material and these remain after
