CC* - Linking crystallographic model and data quality

Kay Diederichs

University of Konstanz, Protein Crystallography and Molecular Bioinformatics, 78457 Konstanz, Germany


Historically, Rmerge (also called Rsym) has been considered as an indicator of X-ray data quality, and e.g. decisions about exposure time, total rotation range, and suitability of datasets for refinement were based on it. Recently it has been pointed out [1] that the high-resolution value of Rmerge is not related to Rwork/Rfree of a crystallographic model, and is therefore unsuitable to define a resolution cutoff. Å more meaningful indicator (CC1/2) has been suggested and a derived quantity (CC*) was shown to be limiting for CCwork/CCfree of a crystallographic model. As a consequence, crystallographers are now in a position to better understand the properties of their data, which may be used to obtain more accurate crystallographic models.


1.       Karplus P. A. and Diederichs K., Science, 2012, 336, 1030-1033