ISOLDE: a physically realistic environment for model building into low-resolution electron-density maps.

Area of Science:

• Structural Biology
• Computational Biology
• Biophysics

Background:

• Macromolecular model refinement is crucial for accurate structural biology.
• Low-resolution cryo-electron microscopy (cryo-EM) data presents unique modeling challenges.
• Existing refinement tools may not adequately address physical realism and validation in low-resolution contexts.

Purpose of the Study:

• Introduce ISOLDE, a novel software package for interactive macromolecular model refinement.
• Provide an intuitive environment for high-fidelity model fitting into electron-density maps.
• Demonstrate ISOLDE's utility in improving model quality and assessing validation metrics.

Main Methods:

• ISOLDE integrates interactive molecular dynamics flexible fitting with advanced molecular graphics.
• Users can directly manipulate atomic models via mouse or haptic interfaces.
• Real-time visualization of validation tasks is incorporated.

Main Results:

• ISOLDE facilitates interactive, physically realistic model refinement.
• Case study on a 3.8 Å resolution cryo-EM structure of the MCM helicase complex shows improved model quality.
• Analysis highlights the limitations of relying solely on validation metrics for low-resolution models.

Conclusions:

• ISOLDE provides an effective solution for high-fidelity macromolecular model refinement.
• The software assists in overcoming common pitfalls associated with low-resolution cryo-EM data.
• A critical perspective on model validation is offered, emphasizing the need for comprehensive assessment.