A simple method for freeze-drying of macromolecules and macromolecular complexes

Area of Science:

• Biophysics
• Electron Microscopy Techniques
• Molecular Biology

Background:

• Traditional methods for preparing large molecules and cellular structures for electron microscopy often face challenges with air-drying artifacts and inconsistent sample thickness.
• Achieving reproducible and thin sample layers is crucial for high-resolution imaging, especially for hydrophobic specimens.

Purpose of the Study:

• To develop a straightforward and effective method for freeze-drying and rotary shadowing of large biological specimens.
• To overcome limitations of existing techniques, ensuring thin sample layers and preserving structural integrity.

Main Methods:

• A novel "glass sandwich" technique involving specimen adsorption to a glass coverslip, stabilization with methanol, freezing in liquid nitrogen, and subsequent shadowing.
• Dissolution of the glass coverslip using hydrofluoric acid after shadowing and replication.
• Modification of the glass substrate's hydrophobicity/hydrophilicity to influence specimen shape.

Main Results:

• The technique effectively freeze-dries and rotary shadows large molecules, molecular assemblies, and cell organelles.
• It reproducibly provides the necessary thin layer of solution for proper freeze-drying, irrespective of sample hydrophobicity.
• Substrate modification influenced the observed shape of macromolecular assemblies like myosin filaments.

Conclusions:

• The "glass sandwich" method offers a simple, reproducible approach for preparing diverse biological samples for high-resolution electron microscopy.
• This technique enhances structural preservation and allows for controlled sample presentation, overcoming common preparation artifacts.