Su, Wu-Pei2019-09-192019-09-19May 20152015-05May 2015Portions of this document appear in: He, Hongxing, and W-P. Su. "Direct phasing of protein crystals with high solvent content." Acta Crystallographica Section A: Foundations and Advances 71, no. 1 (2015): 92-98.https://hdl.handle.net/10657/4889Determining the phases of a diffraction pattern is crucial since the diffraction pattern of a protein crystal yields only the magnitude of the Fourier transform of the electron density. In order to invert the diffraction pattern to get the protein structure, the phase problem must be solved. An iterative transform method is proposed for solving the phase problem in protein crystallography. In each iteration, a weighted average electron-density map is constructed to define an estimated protein mask. Density modifications are then imposed through the histogram matching technique in the protein region, and the hybrid input–output algorithm in the solvent region. Starting from random initial phases, after thousands of iterations the calculated protein mask evolves into the correct shape and the phases converge to the correct values with an average error of 30◦ ∼ 40◦ for high-resolution data for several protein crystals with high solvent content. With the use of non-crystallographic symmetry and other density constraints, the method could potentially be extended to phase protein crystals with less than 50% solvent fraction. The new phasing algorithm can supplement and enhance the traditional refinement tools.application/pdfengThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).Molecular structureProtein X-ray crystallographyPhase problemDirect methodHybrid input-output2019-09-19Thesisborn digital