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Title: Macromolecular phasing


No abstract prepared.

 [1];  [2];
  1. Cornell High Energy Synchrotron Source (CHESS), Cornell University, Ithaca, New York, US
  2. The Macromolecular Diffraction Facility, CHESS
Publication Date:
Research Org.:
Advanced Photon Source (APS); CHESS; Cornell Univ.; Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
OSTI Identifier:
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics Today; Journal Volume: 59; Journal Issue: 3
Country of Publication:
United States

Citation Formats

Shen, Qun, Hao, Quan, and Gruner, Sol M. Macromolecular phasing. United States: N. p., 2006. Web. doi:10.1063/1.2195315.
Shen, Qun, Hao, Quan, & Gruner, Sol M. Macromolecular phasing. United States. doi:10.1063/1.2195315.
Shen, Qun, Hao, Quan, and Gruner, Sol M. Wed . "Macromolecular phasing". United States. doi:10.1063/1.2195315.
title = {Macromolecular phasing},
author = {Shen, Qun and Hao, Quan and Gruner, Sol M.},
abstractNote = {No abstract prepared.},
doi = {10.1063/1.2195315},
journal = {Physics Today},
number = 3,
volume = 59,
place = {United States},
year = {Wed Mar 01 00:00:00 EST 2006},
month = {Wed Mar 01 00:00:00 EST 2006}
  • No abstract prepared.
  • Multiwavelength anomalous diffraction (MAD) and single-wavelength anomalous diffraction (SAD) are the two most commonly used methods for de novo determination of macromolecular structures. Both methods rely on the accurate extraction of anomalous signals; however, because of factors such as poor intrinsic order, radiation damage, inadequate anomalous scatterers, poor diffraction quality and other noise-causing factors, the anomalous signal from a single crystal is not always good enough for structure solution. In this study, procedures for extracting more accurate anomalous signals by merging data from multiple crystals are devised and tested. SAD phasing tests were made with a relatively large (1456 orderedmore » residues) poorly diffracting (d{sub min} = 3.5 {angstrom}) selenomethionyl protein (20 Se). It is quantified that the anomalous signal, success in substructure determination and accuracy of phases and electron-density maps all improve with an increase in the number of crystals used in merging. Structure solutions are possible when no single crystal can support structural analysis. It is proposed that such multi-crystal strategies may be broadly useful when only weak anomalous signals are available.« less
  • The sulfur SAD phasing method allows the determination of protein structuresde novowithout reference to derivatives such as Se-methionine. The feasibility for routine automated sulfur SAD phasing using a number of current protein crystallography beamlines at several synchrotrons was examined using crystals of trimericAchromobacter cycloclastesnitrite reductase (AcNiR), which contains a near average proportion of sulfur-containing residues and two Cu atoms per subunit. Experiments using X-ray wavelengths in the range 1.9–2.4 Å show that we are not yet at the level where sulfur SAD is routinely successful forautomatedstructure solution and model building using existing beamlines and current software tools. On the othermore » hand, experiments using the shortest X-ray wavelengths available on existing beamlines could be routinely exploited to solve and produce unbiased structural models using the similarly weak anomalous scattering signals from the intrinsic metal atoms in proteins. The comparison of long-wavelength phasing (the Bijvoet ratio for nine S atoms and two Cu atoms is ~1.25% at ~2 Å) and copper phasing (the Bijvoet ratio for two Cu atoms is 0.81% at ~0.75Å) forAcNiR suggests that lower data multiplicity than is currently required for success should in general be possible for sulfur phasing if appropriate improvements to beamlines and data collection strategies can be implemented.« less