title: Direct phasing of protein crystals with high solvent content.
abstract: 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. Solvent flattening is then imposed through the hybrid input-output algorithm [Fienup (1982). Appl. Opt. 21, 2758-2769]. Starting from random initial phases, after thousands of iterations the 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, 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.
authors.affiliation: Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204, USA.
authors.forename: Hongxing
authors.initials: H
authors.lastname: He
authors.affiliation: Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204, USA.
authors.forename: Wu Pei
authors.initials: WP
authors.lastname: Su
keywords: ab initio phasing; hybrid input–output algorithm; protein crystallography; solvent flattening