Three-dimensional model-free experimental error correction of protein crystal diffraction data with free-R test.

Experimental error correction and scaling is the last step in X-ray diffraction data processing. It is also critical in obtaining good-quality data. In this study, an algorithm is proposed to more generally and efficiently correct experimental error in X-ray crystal diffraction data. With this algorithm, the experimental error is represented by a symbolic three-dimensional function C(xi, eta, t) in the detecting space. Here, (xi, eta) are the coordinates of the diffraction spots on the image and t represents the data-collection time. While the theoretical form of C(xi, eta, t) is not known, it will be determined from the data through computer-aided analysis. The free R(merge) is introduced to check the validity of the solution. The three-dimensional symbolic function does not carry any assumptions and thus can generally account for experimental errors in various X-ray crystal diffraction experiments that are normally too complicated to be described by any fixed formula. Tests will be given to compare the results from different algorithms.