Labeling and Localization Strategies for In Situ Cryo-Electron Tomography Across the Viral Life Cycle

Area of Science:

• Structural Biology
• Virology
• Microscopy

Background:

• Cryo-electron tomography (Cryo-ET) offers high-resolution visualization of viral structures within native cellular environments.
• A key challenge is unambiguously identifying specific viral components in crowded cellular tomograms due to limitations of electron density interpretation.
• This necessitates robust labeling and localization strategies for accurate structural analysis.

Purpose of the Study:

• To review and evaluate various labeling and localization strategies for in situ Cryo-ET of viral components.
• To provide a practical framework for selecting appropriate methods based on viral protein constraints and life cycle stages.
• To highlight landmark structural discoveries enabled by in situ Cryo-ET in virology.

Main Methods:

• Survey of label-free electron density analysis.
• Evaluation of Cryo-immunogold labeling techniques.
• Assessment of genetically encoded and synthetic molecular tags.
• Review of correlative Cryo-light/electron microscopy (Cryo-CLEM) with Cryo-focused ion beam (Cryo-FIB) milling.

Main Results:

• Cryo-ET enables structural interrogation of viral life cycle events without chemical fixation or heavy metal staining.
• Various strategies, including label-free, immunogold, molecular tags, and Cryo-CLEM/Cryo-FIB, address the identification challenge.
• Landmark structural discoveries across diverse virus families have been achieved using these in situ methods.

Conclusions:

• Effective labeling and localization are crucial for interpreting complex Cryo-ET data of viral components.
• Matching the right strategy to the specific viral protein and life cycle stage is essential for successful structural studies.
• In situ Cryo-ET continues to be a powerful tool for advancing our understanding of viral structures and functions.