High-resolution structure determination of sub-100 kDa complexes using conventional cryo-EM.

Area of Science:

• Structural Biology
• Biophysics
• Biochemistry

Background:

• Determining high-resolution structures of small proteins (<100 kDa) is a key challenge in cryo-electron microscopy (cryo-EM).
• Existing methods like Volta phase plates have limitations in automation and technical feasibility.

Purpose of the Study:

• To demonstrate that conventional defocus-based cryo-EM can achieve high-resolution structures for proteins under 100 kDa.
• To validate the utility of this method for drug-target interaction studies and conformational analysis.

Main Methods:

• Utilized a 200 keV transmission electron microscope with a direct electron detector.
• Employed conventional defocus-based cryo-EM methodologies.
• Processed data to determine high-resolution structures of small proteins.

Main Results:

• Determined a ~2.7 Å structure of alcohol dehydrogenase (82 kDa), resolving bound ligands.
• Obtained ~2.8 Å and ~3.2 Å structures of methemoglobin (64 kDa), identifying distinct conformational states.
• Achieved a sub-nanometer resolution cryo-EM structure for a protein smaller than 50 kDa.

Conclusions:

• Conventional defocus cryo-EM is effective for high-resolution structure determination of small proteins (<100 kDa).
• This approach enables detailed investigation of ligand binding and protein conformational dynamics.
• The method significantly advances the capabilities of cryo-EM for studying small biological macromolecules.