Intermediates in SARS-CoV-2 spike-mediated cell entry.

Area of Science:

• Virology
• Structural Biology
• Biochemistry

Background:

• SARS-CoV-2 enters host cells via spike (S) protein-mediated membrane fusion.
• Stable prefusion and postfusion S protein structures are known, but transient refolding intermediates remain uncharacterized.

Purpose of the Study:

• To capture and characterize transient refolding intermediates of the SARS-CoV-2 S protein during the membrane fusion process.
• To gain mechanistic insights into coronavirus entry for improved inhibitor design.

Main Methods:

• Utilized an antiviral lipopeptide entry inhibitor to trap S protein refolding intermediates.
• Employed cryo-electron tomography to image S protein conformations interacting with hACE2 and proteases on target membranes.

Main Results:

• Successfully captured and imaged extended and partially folded intermediate states of the S2 subunit.
• Identified a novel late-stage conformation on the pathway to membrane fusion.

Conclusions:

• The identified intermediates provide crucial mechanistic insights into the dynamic S protein-directed fusion process.
• These findings may guide the development of novel coronavirus entry inhibitors.