A Description of Imperfections in Protein Crystals

Abstract

An analysis is given of the contribution of various crystal imperfections to the rocking widths of reflections and the divergence of the diffracted beams. The crystal imperfections are the angular spread of the mosaic blocks in the crystal, the size of the mosaic blocks and the variation in cell dimensions between blocks. The analysis has implications for improving crystal perfection, defining data-collection requirements and for dataprocessing procedures. Measurements on crystals of tetragonal lysozyme at room temperature and 100 K were made in order to illustrate how parameters describing the crystal imperfections can be obtained. At 100 K, the dominant imperfection appeared to be a variation in unit-cell dimensions in the crystal.

The R‐factor gap in macromolecular crystallography: an untapped potential for insights on accurate structures

“…were prepared as described in the Experimental procedures, and processed using both MOSFLM and XDS in order to compare and contrast the anomalous signal and other statistical indicators of data quality (Table 1). The mosaic spread reported by MOSFLM for the real dataset was 0.50, and, using a simulated mosaic spread of 0.4 in combination with 0.3% unit cell dispersion as suggested by Nave 25, resulted in a mosaic spread of 0.49 as reported by MOSFLM. XDS uses a different approach for estimating mosaic spread 20, resulting in values of 0.158 for the real data and 0.159 for the simulated data.…”

Accurate macromolecular structures using minimal measurements from X-ray free-electron lasers

“…As described in the Supplementary Note, the underlying phenomenon treated by that model (large λ/a ratio, where λ is the wavelength of the incident light, and a is the crystal width) does not apply for high-resolution experiments. In fact, it is not possible to identify a single criterion to describe the spot shape throughout the data sets; some images exhibit concentric arcs consistent with mosaic spread 37 (not shown), while other images contain elongation that is chiefly radial (Fig. 1e).…”

Investigating the Effect of Impurities on Macromolecule Crystal Growth in Microgravity

“…The linearity is expected if there is little or no contribution of the mosaicity to internal domain variation. 38,39 For the 1.8% dimer case, mosaicity increases with resolution. This is indicative of disorder within the individual domains that make up the crystal.…”

“…It is a measure of the angular size of the reflection profile after correction for the effects of the beam nonideality and diffraction geometry. Mosaicity is due to a combination of three causes: 38,39 angular misalignment of domains within the crystal, finite domain volume, and lattice strain. In previous microgravity experiments, the reduced crystal mosaicity reported for lysozyme 4 and thaumatin 5 were observed to be from the increase of domain sizes within the crystals.…”