Biomolecular Crystals Research Articles

High Resolution Imaging as a Characterization Tool for Biological Crystals

Biomolecular crystals consist of large unit cells that form a rather flexible medium that is able to accommodate a certain degree of lattice distortion, leading to several interesting issues ranging from structural to physical properties. Several techniques, from X-ray diffraction to microscopy, have been adapted to study the structural and physical properties of biomolecular crystals systematically. The use of synchrotron-based monochromatic X-ray diffraction topography, with triple axis diffractometry and rocking curve measurements, to characterize biomolecular crystals is reviewed. Recent X-ray diffraction images from gel and solution grown lysozyme crystals are presented. Defect structures in these crystals are discussed, together with reciprocal space mapping, and compared with results obtained from crystals grown in a low gravity environment.

Why biomolecules prefer only a few crystal structures.

We have shown that, in determining the biomolecule-crystal symmetry, the occupation of low-site-symmetry Wyckoff positions is crucial, which contrasts with the overwhelming majority of nonmolecular, inorganic crystals where atoms mainly reside in high-symmetry Wyckoff positions. We consider the general relation between the symmetry of an isolated molecule and the possible symmetries of biomolecular crystals it can generate. We reveal that the improper symmetry operations (inversion and mirror symmetries) are prohibited in the chirally pure biomolecular crystals. Next, we show that the low (C1) symmetry of large biological molecules substantially decreases the space in a crystal where the molecules can reside. The space "forbidden" for molecule centers is found to be in the R vicinity of the higher-symmetry Wyckoff positions on symmetry lines, where R is the molecule characteristic size. The remaining free space and hence the probability for the structure to exist are shown to be drastically increased when replacing any rotation axis by a screw one. Based on the proposed model, we have explained the peculiar distribution of biomolecular crystals over the space groups, which can be obtained from biomolecule-crystal databases.

Biomolecular crystals: from X-ray diffraction topography to reciprocal space mapping

Biomolecular crystals: from X-ray diffraction topography to reciprocal space mapping

Fourth-generation X-ray sources: some possible applications to biology

The term 'fourth generation X-ray sources' has come to mean X-ray free-electron lasers which use multi-GeV electron beams from linear accelerators to generate X-rays by self-amplified stimulated emission when fired into long undulators. Properties of the radiation expected from such sources are reviewed briefly and two possible applications of the resulting pulsed highly collimated X-radiation to problems in biology are discussed: use of X-ray photon correlation spectroscopy to measure time correlations of atoms in protein crystals, and use of Mössbauer radiation extracted from the photon beams by resonant Bragg diffraction from (57)Fe-containing crystals, for MAD phasing of very large unit-cell biomolecular crystals and possibly for photon echo measurements.