International
Tables for
Crystallography
Volume F
Crystallography of biological macromolecules
Edited by M. G. Rossmann and E. Arnold

International Tables for Crystallography (2006). Vol. F, ch. 9.1, p. 194   | 1 | 2 |

Section 9.1.15. Data quality over the whole resolution range

Z. Dautera* and K. S. Wilsonb

aNational Cancer Institute, Brookhaven National Laboratory, NSLS, Building 725A-X9, Upton, NY 11973, USA, and bStructural Biology Laboratory, Department of Chemistry, University of York, York YO10 5DD, England
Correspondence e-mail:  dauter@bnl.gov

9.1.15. Data quality over the whole resolution range

| top | pdf |

It is not possible to judge data quality from a single global parameter, especially [R_{\rm merge}], not even from the overall [I/\sigma (I)] ratio. Such a parameter may totally neglect problems such as the omission of all low-resolution terms due to detector saturation. A set of key parameters including [I/\sigma (I)], [R_{\rm merge}], percentage completeness, redundancy of measurements and number of overloaded high-intensity measurements must be tabulated in a series of resolution shells. This information should be assessed during data collection to guide the experimenter in the optimization of such parameters as exposure time, attainable resolution and required redundancy. As stated in Section 9.1.13[link], the requirements will vary with the application.

The effect of sample decay also requires such tables. The X-ray intensities decay more rapidly at high angle than at low, and consideration of this effect requires knowledge of the relative B values that need to be applied to the individual images during data scaling. An often subjective decision will need to be made regarding at what stage the decay is sufficiently high that further images should be ignored. The effects of damage are likely to be systematic rather than just random, and cannot be totally compensated for by scaling. This remains true even for cryogenically frozen crystals, especially with ultra bright synchrotron sources.

Following an earlier recommendation by the IUCr Commission on Biological Molecules (Baker et al., 1996[link]), this tabulated information, as a function of resolution, should be deposited with the data and the final model coordinates in the Protein Data Bank. Only then is it possible to have a true record of the experiment and for users of the database to judge the correctness and information content of a structural analysis.

References

Baker, E. N., Blundell, T. L., Vijayan, M., Dodson, E., Dodson, G., Gilliland, G. L. & Sussman, J. L. (1996). Deposition of macromolecular data. Acta Cryst. D52, 609.








































to end of page
to top of page