A Multi-Channel Multi-Dimensional Histogram Mapping Method For Macromolecular Phase Extension And Refinement. Shibin Xiang, Dept. of Biochemistry & Biophysics, Univ. of North Carolina, Chapel Hill, NC 27599-7260

A multi-channel, multi-dimensional histogram mapping method and the software PDnR (phase determination and refinement) are described. In PDnR, stereochemical information in an ideal molecular electron density map is modeled by a multi-dimensional histogram composed of the density value and the gradient magnitude and Laplacian of the density. Phase extension and refinement are achieved by imposing this information, as a target, on an electron density map with phase errors through multidimensional histogram mapping. The electron density map is divided into different channels: the solvent, the protein and the known fragment. In each channel, the multi-dimensional histogram mappings are carried out separately.

Tests on simulated data of cytidine deaminase have shown that PDnR is capable of reducing average phase errors from 75[ring] to 25[ring]. Similar improvements are also observed from tests on experimental data sets.