Prof. Zhijie Liu’s recent Acta Crystallographica A paper "A multi-dataset data-collection strategy produces better diffraction data" (http://journals.iucr. org/a/issues/2011/06/00/issconts.html) reports a new strategy for collecting crystallography diffraction data for biological macromolecular crystals.

Prof. Liu’s group at the Institute of Biophysics, Chinese Academy of Sciences and collaborators at the University of Georgia, USA, used theoretical deduction and experimental testing to develop a MDS (Multi-DataSet) data collection method. This method can be used to obtain higher-quality diffraction data using the same X-ray radiation dose as traditional methods.

Crystal diffraction data provides three-dimensional structural information on crystallized molecules. The quality of this data directly affects the accuracy, quality and reliability of detailed structure determination and model building. Prof Liu’s group first show theoretically that, given the same experimental conditions and dose of X-rays, repeated MDS data collections should effectively improve the quality of diffraction data by reducing data collection errors. They then provide experimental proof of the validity of MDS methods by developing a data-quality evaluation process, termed a “readiness test” for the X-ray data-collection system, and using the anomalous signals of sulfur atoms in zinc-free insulin crystals to probe the quality of data collected using different data-collection strategies. Calculations from the diffraction data of six insulin crystals collected using two different data-collection systems showed that the diffraction data collected with the MDS strategy contained more accurate anomalous signals from sulfur atoms than data collected with a regular single-path data-collection strategy.

The MDS strategy offers additional advantages with respect to radiation-damage-sensitive crystals and can also be employed for in-house data collection using a rotating-anode X-ray source, since the relatively weaker X-ray beam intensity is more suitable for multiple data-collection experiments. The readiness test of the X-ray data collection system developed also has potential to be applied as a sensitive and simple tool for X-ray data collection system evaluation and optimization.

Figure 1 Superposition of the rigid body refined insulin molecule model and the S-SAD phased experimental 2fo-fc electron density map at 50.0 – 2.5 angstrom resolution contoured at 1.0σ. A: Map calculated using regular exposed data for crystal 1. The arrow signs in the figure indicate missing density at the mainchain area; B: Map calculated using MDS exposed data for crystal 1.