Variable Resolution Maps (VRM) in CCTBX and Phenix: Accounting For Local Resolution In cryoEM

Area of Science:

• Structural biology
• Biophysical chemistry
• Computational crystallography

Background:

• Density map calculation is crucial for structural studies in crystallography and cryo-electron microscopy (cryoEM).
• Accurate comparison of calculated and experimental maps is challenging due to varying resolution in cryoEM data.
• Existing methods often use uniform resolution or simplified functions, not fully accounting for local resolution variations.

Purpose of the Study:

• To implement a novel method for computing atomic model density maps that accounts for local resolution.
• To enhance the accuracy of fitting atomic models to experimental structural data.
• To integrate this method into widely used software packages, CCTBX and Phenix.

Main Methods:

• Implementation of a new method for calculating variable-resolution maps based on analytic functions of atomic parameters.
• Incorporation of local resolution information directly into the map calculation process.
• Integration of the method into the CCTBX computational library and the Phenix software suite.

Main Results:

• Development of tools within CCTBX and Phenix for calculating variable-resolution density maps.
• The new method accurately represents local resolution variations across the map.
• Analytically differentiable functions are used, enabling improved model parameterization and refinement.

Conclusions:

• The implemented method provides a more accurate representation of atomic models in the context of experimental data, especially for cryoEM.
• This advancement facilitates more precise atomic model building, refinement, and validation in structural studies.
• The availability in CCTBX and Phenix makes this advanced capability accessible to the structural biology community.