Retrovirus envelope protein complex structure in situ studied by cryo-electron tomography

Area of Science:

• Structural Biology
• Virology
• Biophysics

Background:

• Retrovirus envelope glycoproteins (Env) are crucial for viral entry.
• Understanding Env structure is key to developing antiviral strategies.
• Previous structural studies often lacked resolution or were performed on isolated components.

Purpose of the Study:

• To determine the 3D structure of intact Moloney murine leukemia retrovirus Env complexes.
• To provide insights into the prefusion conformation of retroviral surface proteins.
• To develop advanced imaging techniques for studying intact viruses.

Main Methods:

• Cryo-electron tomography (cryo-ET) for 3D imaging of frozen-hydrated retrovirus particles.
• Single-particle averaging techniques to enhance resolution.
• Development of an iterative 3D averaging algorithm to overcome the
• missing-wedge
• effect and improve signal-to-noise ratio.

Main Results:

• Determined the trimeric structure of Env at 2.7 nm resolution, resolving individual domains.
• The 3D reconstruction revealed a tripod-like shape where the trimer penetrates the membrane at three distinct sites.
• Enabled tentative docking of the receptor-binding domain structure.

Conclusions:

• Provides unprecedented 3D structural information of an intact retrovirus surface protein in its prefusion state.
• The novel tripod structure offers new perspectives on Env-membrane interactions.
• This study advances cryo-ET and averaging methods for studying complex biological macromolecules in situ.