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Title: Improving experimental phases for strong reflections prior to density modification

A genetic algorithm has been developed to optimize the phases of the strongest reflections in SIR/SAD data. This is shown to facilitate density modification and model building in several test cases. Experimental phasing of diffraction data from macromolecular crystals involves deriving phase probability distributions. These distributions are often bimodal, making their weighted average, the centroid phase, improbable, so that electron-density maps computed using centroid phases are often non-interpretable. Density modification brings in information about the characteristics of electron density in protein crystals. In successful cases, this allows a choice between the modes in the phase probability distributions, and the maps can cross the borderline between non-interpretable and interpretable. Based on the suggestions by Vekhter [Vekhter (2005 ▶), Acta Cryst. D61, 899–902], the impact of identifying optimized phases for a small number of strong reflections prior to the density-modification process was investigated while using the centroid phase as a starting point for the remaining reflections. A genetic algorithm was developed that optimizes the quality of such phases using the skewness of the density map as a target function. Phases optimized in this way are then used in density modification. In most of the tests, the resulting maps were of higher qualitymore » than maps generated from the original centroid phases. In one of the test cases, the new method sufficiently improved a marginal set of experimental SAD phases to enable successful map interpretation. A computer program, SISA, has been developed to apply this method for phase improvement in macromolecular crystallography.« less
Authors:
 [1] ;  [2] ;  [1] ;  [3] ;  [4] ;  [5] ;  [2]
  1. University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck (Germany)
  2. (Germany)
  3. (China)
  4. Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
  5. University of Cambridge, Cambridge CB2 0XY (United Kingdom)
Publication Date:
OSTI Identifier:
22347827
Resource Type:
Journal Article
Resource Relation:
Journal Name: Acta Crystallographica. Section D: Biological Crystallography; Journal Volume: 69; Journal Issue: Pt 10; Other Information: PMCID: PMC3792643; PMID: 24100322; PUBLISHER-ID: dz5285; OAI: oai:pubmedcentral.nih.gov:3792643; Copyright (c) Uervirojnangkoorn et al. 2013; This is an open-access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
Denmark
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ALGORITHMS; ASYMMETRY; COMPUTER CODES; CRYSTALS; DENSITY; DIFFRACTION; DISTRIBUTION; ELECTRON DENSITY; ELECTRONS; MODIFICATIONS; PROBABILITY; PROTEINS; REFLECTION; STATISTICS