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Related Experiment Videos

Phase improvement by cross-validated density modification.

A L Roberts1, A T Brünger

  • 1The Howard Hughes Medical Institute and Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.

Acta Crystallographica. Section D, Biological Crystallography
|November 1, 1995
PubMed
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A new cross-validated R value helps optimize crystallographic phase determination by assessing solvent flattening accuracy. This method reduces overfitting risks and improves structural model reliability.

Area of Science:

  • Crystallography
  • Structural Biology
  • Biophysics

Background:

  • Solvent flattening is a standard technique in crystallographic structure determination.
  • It can fail with poor initial phases, leading to incorrect parameterization and data misinterpretation.
  • Overfitting is a significant risk in phase refinement.

Purpose of the Study:

  • To implement and validate a cross-validated (free) R value for assessing solvent flattening.
  • To mitigate the risks of overfitting and misinterpretation in crystallographic phasing.
  • To provide a reliable metric for optimizing density modification procedures.

Main Methods:

  • Implemented a free R value calculation using experimental and calculated structure factors.
  • Calculated the free R value from solvent-flattened electron density via inverse Fourier transform.

Related Experiment Videos

  • Assessed reliability by correlating free R values with known phase errors in test cases.
  • Investigated sensitivity to test set selection and low-resolution data.

    • Main Results:

    • A high correlation was observed between the free R value and phase errors.
    • The free R value effectively reflects variations in negative density elimination and phase combination weighting.
    • Complete cross-validation may be necessary for low-resolution data.
    • The method demonstrated reliability in optimizing parameters.

    Conclusions:

    • The free R value is a reliable metric for optimizing solvent flattening and density modification.
    • It effectively reduces the risk of overfitting and aids in accurate crystallographic structure determination.
    • This approach provides an independent phase error estimate when unavailable.
    • Enhances the robustness of crystallographic phase refinement.