'Broken symmetries' in macromolecular crystallography: phasing from unmerged data

Area of Science:

• Crystallography
• Structural Biology
• X-ray Diffraction

Background:

• Crystal structures exhibit space-group symmetry, which dictates point-group symmetry in diffraction patterns, creating symmetry-equivalent reflections.
• In macromolecular crystallography, this reciprocal space symmetry can be disrupted by factors like radiation damage or polarization anisotropy of anomalous scattering.
• Typically, data merging and phasing are separate steps in structure solution.

Purpose of the Study:

• To explore how broken symmetry in diffraction patterns can be leveraged for phase information in macromolecular crystallography.
• To present an integrated approach that abandons the conventional separation of data merging and phasing.

Main Methods:

• Investigating instances where symmetry-equivalent reflections are no longer equivalent due to site-specific radiation damage during X-ray measurements.
• Analyzing broken symmetry arising from the polarization anisotropy of anomalous scattering.
• Developing a method where unmerged diffraction data are analyzed down to the Harker construction.

Main Results:

• Demonstrating that genuine intensity differences between symmetry-related reflections, when symmetry is broken, can yield valuable phase information.
• Explicitly modeling and refining symmetry-breaking effects at the Harker construction stage.
• Showing that these symmetry-breaking effects serve as a source of supplementary phase information.

Conclusions:

• Broken symmetry in macromolecular crystallography is not merely an artifact but a source of exploitable phase information.
• An integrated approach, keeping data unmerged until the Harker construction, allows for the modeling of symmetry-breaking effects.
• This novel strategy enhances the structure-solution process by incorporating supplementary phase information derived from broken symmetry.