emClarity: software for high-resolution cryo-electron tomography and subtomogram averaging.

Area of Science:

• Structural Biology
• Biophysics
• Biochemistry

Background:

• Macromolecular complexes are flexible and difficult to purify for single-particle cryo-electron microscopy (cryo-EM).
• Cryo-electron tomography (cryo-ET) with subtomogram analysis offers insights into complex structures but struggles with heterogeneity and low abundance.
• Current methods face challenges in achieving high resolution and distinguishing functional states of heterogeneous complexes.

Purpose of the Study:

• To develop an advanced image-processing package, emClarity, for improved cryo-electron tomography analysis.
• To enhance the resolution and classification capabilities for studying heterogeneous macromolecular complexes.
• To provide a robust computational tool for analyzing low-abundance and conformationally diverse biological samples.

Main Methods:

• Developed emClarity, a GPU-accelerated package featuring an iterative tomographic tilt-series refinement algorithm.
• Utilized subtomograms as fiducial markers within the refinement process.
• Implemented a 3D-sampling-function-compensated, multi-scale principal component analysis for classification.

Main Results:

• Achieved substantial improvements in map resolution for macromolecular complexes.
• Demonstrated enhanced separation of different functional states within heterogeneous samples.
• Showcased superior performance compared to current state-of-the-art cryo-ET software.

Conclusions:

• emClarity significantly advances the structural analysis of flexible and heterogeneous macromolecular complexes using cryo-ET.
• The developed methods enable higher resolution structure determination and better discrimination of functional states.
• This tool provides a powerful approach for studying challenging biological specimens in structural biology.