Abstract
A multi-dataset (MDS) data-collection strategy is proposed and analyzed for macromolecular crystal diffraction data acquisition. The theoretical analysis indicated that the MDS strategy can reduce the standard deviation (background noise) of diffraction data compared with the commonly used single-dataset strategy for a fixed X-ray dose. In order to validate the hypothesis experimentally, a data-quality evaluation process, termed a readiness test of the X-ray data-collection system, was developed. The anomalous signals of sulfur atoms in zinc-free insulin crystals were used as the probe to differentiate the quality of data collected using different data-collection strategies. The data-collection results using home-laboratory-based rotating-anode X-ray and synchrotron X-ray systems indicate that the diffraction data collected with the MDS strategy contain more accurate anomalous signals from sulfur atoms than the data collected with a regular data-collection strategy. In addition, the MDS strategy offered more advantages with respect to radiation-damage-sensitive crystals and better usage of rotating-anode as well as synchrotron X-rays.
Highlights
The X-ray diffraction data of crystals contain the critical threedimensional structural information of the crystallized molecules; they are the only direct experimental source for subsequent elucidation of spatial structures of the crystallized molecules
The factors can be categorized into three groups. (i) Crystal: the diffraction quality is based on the internal degree of order of the molecules and the mosaicity of the crystal, and the cryofreezing status such as the selection of cryo solution, loop and cryo treatment. (ii) Instrumentation: the X-ray beam quality, goniometry and the quality of the detectors [dark current correction, balance of different mosaic chips, sensitivity, dynamic range, detective quantum efficiency (DQE) etc.]. (iii) Data-collection strategy: the wavelength, attenuation, detector-to-crystal distance, exposure time, start angle, scan range and oscillation angle
The theoretical analysis indicated that the data collected with the MDS strategy are of better quality than the data collected with the regular strategy
Summary
The X-ray diffraction data of crystals contain the critical threedimensional structural information of the crystallized molecules; they are the only direct experimental source for subsequent elucidation of spatial structures of the crystallized molecules. 544 doi:10.1107/S0108767311037469 crystal and X-ray data-collection system, the key to obtaining the highest possible quality of diffraction data lies in the datacollection strategy (Cianci et al, 2008; Sarma & Karplus, 2006). Obtaining accurate and complete diffraction data sets of macromolecular crystals within their lifetime is very important (Gonzalez, 2003; Leal, 2011; Yang et al, 2003). The theoretical analysis indicates that the MDS data-collection strategy at a fixed X-ray dose produces betterquality data. In order to validate the hypothesis experimentally, a data-quality evaluation process, termed a readiness test of the X-ray data-collection system, was developed. Zinc-free insulin crystals were used as the standard testing crystals and the anomalous signals of sulfur atoms in insulin crystals were used as an indicator to differentiate the quality of data collected using the different data-collection strategies
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