Anisotropy in diffraction qualities of crystals may represent a serious threat to the structure determination process. When the differences in various directions of the reciprocal space exceed the range of 0.5 Å resolution, problems with phasing may arise, and the structure refinement process is frequently unstable. Such difficulties also appear for structures with high resolution. Although a limited number of tools for the data analysis is available, the current praxis is not standardized and needs thorough revision.
We analyzed diffraction data from a crystal of an engineered protein binder with a promising application as a protein therapeutics [1]. The protein crystallized in space group I4122. The initial diffraction data quality indicators of the data processed the standard way suggested the high-resolution diffraction limit at 2.9 Å. However, a combination of data processed with STARANISO [2] and paired refinement with PAIREF [3] showed a possible extension of the diffraction limit to 2.6 Å in the direction along the l axis. Calculated electron density display moderate improvement and easier interpretation for some side chains.
This work was supported by MEYS CR (projects CAAS – CZ.02.1.01/0.0/0.0/16_019/0000778) from the ERDF fund and by the GA CTU in Prague (SGS22/114/OHK4/2T/14).