Growing crystals for x-ray free-electron laser structural studies of biomolecules and their complexes

Currently, X-ray crystallography, which typically uses synchrotron sources, remains the dominant method for structural determination of proteins and other biomolecules. However, small protein crystals do not provide sufficiently high-resolution diffraction patterns and suffer radiation damage; therefore, conventional X-ray crystallography needs larger protein crystals. The burgeoning method of serial crystallography using X-ray free-electron lasers (XFELs) avoids these challenges: it affords excellent structural data from weakly diffracting objects, including tiny crystals. An XFEL is implemented by irradiating microjets of suspensions of microcrystals with very intense X-ray beams. However, while the method for creating microcrystalline microjets is well established, little attention is given to the growth of high-quality nano/microcrystals suitable for XFEL experiments. In this study, in order to assist the growth of such crystals, we calculate the mean crystal size and the time needed to grow crystals to the desired size in batch crystallization (the predominant method for preparing the required microcrystalline slurries); this time is reckoned theoretically both for microcrystals and for crystals larger than the upper limit of the Gibbs–Thomson effect. The impact of the omnipresent impurities on the growth of microcrystals is also considered quantitatively. Experiments, performed with the model protein lysozyme, support the theoretical predictions

Theoretical and experimental investigation on protein crystal nucleation in pores and crevices

The nucleation ability of pores is explained using the equilibration between the cohesive energy maintaining the integrity of a crystalline cluster and the destructive energy tending to tear it up. It is shown that to get 3D crystals it is vital to have 2D crystals nucleating in the pores first. By filling the pore orifice, the 2D crystal nuclei are more stable because their peripheries are protected from the destructive action of water molecules. Furthermore, the periphery of the 2D crystal is additionally stabilized as a result of its cohesion with the pore wall. The understanding provided by this study combining theory and experiment will facilitate the design of new nucleants