Dynamics of Layer Growth in Protein Crystallization.

Proteins are the elementary building units for all living creatures and are essential components for information and energy processing in living systems. The need to understand genome structure-function correlations for this group of natural compounds has emerged as a focus of intense recent investigations.1 Although advances in nuclear magnetic resonance techniques continue to increase the upper limit to the size of protein molecules that can be studied by this method,2 the diffraction of X-rays, electrons, or neutrons is the most widely used method for protein structure investigations. To resolve atoms that are, typically, 1.5-2 Å apart, these diffraction methods require single crystals that are as large as several tenths of a millimeter in all three dimensions and have low defect contents and high compositional and structural uniformity. Recent advances in protein expression, characterization, and purification techniques, as well as beam and detector technology and in computational crystallography, have greatly accelerated the rate at which protein structures can be solved.3 However, the preparation of diffractionquality crystals has emerged as the bottleneck in the route toward macromolecular crystal structure determinations.4,5 Beyond protein single-crystal growth, progress in various biochemical and biomedical research and production tasks is impeded by lack of insight into protein nucleation and growth mechanisms. For instance, the slow dissolution rate of protein crystals is used to achieve sustained release of medications, such as insulin.6-10 Work on the crystallization of other proteins that can be dispensed in a similar manner (e.g., interferon-R and human growth hormone) is currently underway. If the administered dose consists of a few, larger, equidimensional crystallites, steady medication release rates can be maintained for longer periods than for doses comprised of many smaller crystallites. To achieve such