Modeling, docking, and fitting of atomic structures to 3D maps from cryo-electron microscopy.

Area of Science:

• Structural Biology
• Biophysics
• Computational Biology

Background:

• Electron microscopy (EM) and image analysis are powerful tools for determining macromolecular complex structures.
• EM's versatility allows analysis of molecules unsuitable for X-ray crystallography or NMR spectroscopy.
• Low resolution of EM maps often precludes direct atomic model building via chain tracing.

Purpose of the Study:

• To describe a computational workflow for analyzing EM structures at atomic resolution.
• To illustrate the integration of homology modeling, model fitting, and domain docking.
• To determine the structure and domain organization of the integral membrane protein CopA.

Main Methods:

• Building a homology model based on related protein structures (e.g., SERCA).
• Fitting the homology model into a low-resolution EM map (17 Å).
• Utilizing computational software for docking unique domains, such as the metal-binding domain (MBD) of CopA.

Main Results:

• A homology model of CopA was successfully fitted to the EM map.
• Computational docking identified plausible interfaces for the MBD.
• EM map constraints guided the selection of a unique and accurate MBD location.
• Atomic details of the domain interface were elucidated.

Conclusions:

• The synergistic combination of EM and computational modeling enables atomic-level structural determination.
• This workflow is effective for localizing novel domains and understanding conformational changes.
• The study provides insights into the structure of the copper pump CopA and its unique MBD.