Characterization Standard for In-situ Cryo-electron Tomography

Area of Science:

• Structural Biology
• Microscopy Techniques
• Biophysics

Background:

• Standardized biological specimens are crucial for optimizing cryo-electron microscopy (cryoEM) workflows and benchmarking instrument performance.
• Apoferritin serves as a standard for single-particle analysis, but a similar benchmark is lacking for cryo-electron tomography (cryo-ET).
• Ribosomes are commonly used in cryo-ET but require large datasets due to C1 symmetry and structural heterogeneity, hindering rapid optimization and standardized comparisons.

Purpose of the Study:

• To introduce a scalable in situ benchmark for cryo-electron tomography (cryo-ET).
• To provide a standardized specimen for optimizing cryo-ET workflows and validating instrument performance.

Main Methods:

• Overexpression of PP7 virus-like particles (VLPs) in *E. coli*.
• Utilizing the high symmetry of VLPs for rapid validation.
• Employing distinct structural features of VLPs as a resolution metric.

Main Results:

• PP7 VLPs serve as a scalable in situ benchmark for cryo-ET.
• High symmetry of VLPs allows for high-resolution validation of tomographic pipelines with minimal datasets.
• Distinct structural features provide a practical resolution metric across various resolutions.

Conclusions:

• PP7 VLPs are a suitable replacement for ribosomes as a standard in cryo-ET.
• This VLP benchmark facilitates rapid optimization and standardized comparison of cryo-ET workflows.
• The use of PP7 VLPs can accelerate advancements in cryo-ET methodology and application.