Coronaviruses Use ACE2 Monomers as Entry-Receptors

Area of Science:

• Cell biology
• Virology
• Microscopy

Background:

• Angiotensin-converting enzyme 2 (ACE2) acts as the cellular entry receptor for SARS-CoV-2.
• SARS-CoV-2 utilizes its trimeric spike (S) proteins to bind ACE2 on host cells.
• Previous hypotheses suggested that SARS-CoV-2 S proteins bind to clustered ACE2 receptors for efficient infection.

Purpose of the Study:

• To visualize and quantify the distribution of endogenous ACE2 receptors on cell surfaces.
• To investigate whether SARS-CoV-2 S protein binding induces ACE2 receptor oligomerization.
• To determine the minimum ACE2 receptor interaction required for SARS-CoV-2 infection.

Main Methods:

• Direct stochastic optical reconstruction microscopy (dSTORM) was employed for high-resolution imaging.
• Various labeling strategies were utilized to detect ACE2 receptors and S proteins.
• Infection studies using engineered vesicular stomatitis virus (VSV) particles bearing S proteins were conducted.

Main Results:

• Endogenous ACE2 receptors exist as monomers on the plasma membrane at low densities (1-2 receptors/μm²).
• Binding of SARS-CoV-2 S proteins does not lead to the formation of ACE2 oligomers.
• A single S protein interaction with a monomeric ACE2 receptor is sufficient for viral infection.

Conclusions:

• SARS-CoV-2 infects cells via monomeric ACE2 receptors, not clustered ones.
• The low-density, monomeric nature of ACE2 contributes to the high infectivity of SARS-CoV-2.
• This study reframes the understanding of the initial molecular interactions driving SARS-CoV-2 cell entry.