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Related Experiment Videos

Twinned crystals and anomalous phasing.

Zbigniew Dauter1

  • 1Synchrotron Radiation Research Section, National Cancer Institute, Brookhaven National Laboratory, Building 725A-X9, Upton, NY 11973, USA. dauter@bnl.gov

Acta Crystallographica. Section D, Biological Crystallography
|October 24, 2003
PubMed
Summary
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Crystal twinning, a common issue in crystallography, can be overcome using statistical methods. Even with a twin fraction of 0.5, the single-wavelength anomalous diffraction (SAD) method can successfully determine crystal structures.

Area of Science:

  • Crystallography
  • Structural Biology
  • X-ray Diffraction

Background:

  • Crystal twinning, including merohedral and pseudomerohedral types, is often undetectable from direct diffraction pattern inspection.
  • Statistical analysis of diffraction intensities offers methods for identifying twinning and estimating the twin fraction in macromolecular crystals.
  • Detwinning procedures can refine diffraction data but introduce inaccuracies, especially when the twin fraction approaches 0.5.

Purpose of the Study:

  • To investigate the feasibility of solving crystal structures from twinned data, particularly in challenging cases.
  • To evaluate the effectiveness of the single-wavelength anomalous diffraction (SAD) method for detwinning macromolecular crystal data.

Main Methods:

  • Statistical analysis of diffraction intensities to estimate twin fraction.

Related Experiment Videos

  • Application of the single-wavelength anomalous diffraction (SAD) method.
  • Testing calculations using data from a twinned crystal of gpD, the bacteriophage lambda capsid protein.

    • Main Results:

    • Crystal twinning identification and twin fraction estimation rely on statistical properties of diffraction intensities.
    • Detwinning procedures can improve data but introduce errors, particularly at high twin fractions (near 0.5).
    • The SAD method proved effective in solving the structure of gpD even with a twin fraction of 0.5, indicating its robustness.

    Conclusions:

    • Standard crystallographic techniques can sometimes solve structures from twinned data.
    • The SAD method is a viable approach for structure determination from twinned crystals, even in cases of perfect twinning (twin fraction of 0.5).
    • This finding offers a potential solution for challenging crystallographic datasets affected by twinning.