Envelope structure of Semliki Forest virus reconstructed from cryo-electron micrographs

Area of Science:

• Structural biology
• Virology
• Cryo-electron microscopy

Background:

• Enveloped viruses are challenging to study due to resistance to crystallization and deformation during preparation.
• Conventional electron microscopy and X-ray crystallography have limitations for enveloped virus structural determination.

Purpose of the Study:

• To develop and apply a cryo-electron microscopy method for high-resolution structural analysis of enveloped viruses.
• To overcome the limitations of conventional techniques in studying enveloped virus architecture.

Main Methods:

• Utilized cryo-electron microscopy with unfixed, unstained viruses in vitrified suspension.
• Employed a novel 'reconstruction by optimized series expansion' (ROSE) method to combine images of multiple virus particles.
• Addressed electron beam damage by combining views from numerous differently oriented viruses.

Main Results:

• Achieved a 3.5-nm resolution reconstruction of the Semliki Forest virus envelope.
• Visualized the T = 4 surface lattice geometry.
• Determined the shape of trimeric spikes and their arrangement on the lipid bilayer.

Conclusions:

• The developed cryo-EM method and ROSE technique are effective for high-resolution structural studies of enveloped viruses.
• Detailed structural features of the Semliki Forest virus envelope have been elucidated.
• This approach provides new insights into the architecture of enveloped viruses.