Constructing atomic structural models into cryo-EM densities using molecular dynamics - Pros and cons.

Area of Science:

• Structural Biology
• Computational Biology
• Biophysics

Background:

• Accurate atomic model building from low-resolution electron density maps (3-5 Å) is challenging.
• Balancing global/local sampling and stereochemical correctness is crucial for hybrid structure determination.
• Molecular Dynamics Flexible Fitting (MDFF) offers a robust approach for this balance.

Purpose of the Study:

• To evaluate the performance of the ReMDFF method for hybrid structure determination.
• To compare ReMDFF-generated models against independent entries in the 2015-2016 Cryo-EM Model Challenge.
• To identify key factors influencing ReMDFF model quality and establish best practices.

Main Methods:

• Utilized ReMDFF, a resolution-exchange scheme within MDFF, for structure determination.
• Applied ReMDFF to high-resolution density maps of β-galactosidase (3.2 Å) and TRPV1 (3.4 Å).
• Compared ReMDFF models against independent entries from the Cryo-EM Model Challenge using Molprobity analysis.

Main Results:

• ReMDFF models demonstrated high scores for quality-of-fit and quality-of-model.
• Systematic discrepancies were observed via Molprobity analysis, consistent across multiple entries.
• Force field parameters and initial model choice significantly impacted ReMDFF model quality.
• Newly developed CHARMM36m force field parameters yielded more refined models.

Conclusions:

• ReMDFF is a powerful tool for hybrid structure determination, achieving a good balance of sampling and stereochemistry.
• Molprobity analysis revealed areas for improvement in data-guided real-space refinements.
• Optimizing force field parameters and initial models is critical for maximizing ReMDFF performance.
• Best practices are recommended to enhance community adoption of MDFF developments.