Model-based local density sharpening of cryo-EM maps.

Area of Science:

• Structural Biology
• Biophysics
• Biochemistry

Background:

• Atomic models are the final output of cryo-electron microscopy (cryo-EM) structure determination.
• High-resolution cryo-EM density maps are crucial for accurate atomic model building.
• Variations in resolution within cryo-EM maps can hinder model interpretation and refinement.

Purpose of the Study:

• To introduce a general procedure for local sharpening of cryo-EM density maps.
• To improve the interpretability of cryo-EM density maps, especially those with resolution variations.
• To facilitate the process of atomic model building and refinement using sharpened cryo-EM data.

Main Methods:

• A general procedure for local sharpening of cryo-EM density maps was developed.
• The method utilizes prior knowledge of an atomic reference structure.
• Density map contrast is optimized by amplitude scaling against a radially averaged local falloff estimated from a windowed reference model.

Main Results:

• The local sharpening procedure was tested on six diverse cryo-EM structures (TRPV1, β-galactosidase, γ-secretase, ribosome-EF-Tu complex, 20S proteasome, and RNA polymerase III).
• Local sharpening was shown to increase the interpretability of cryo-EM density maps.
• The method proved particularly effective in regions with resolution variation.

Conclusions:

• Local sharpening of cryo-EM density maps enhances interpretability and aids in atomic model building and refinement.
• This procedure offers a valuable tool for analyzing cryo-EM data with varying resolution.
• The method provides a generalizable approach applicable to a wide range of biological macromolecules.