Mass Photometry Reveals Distinct ACE2 Binding Stoichiometries across SARS-CoV-2 Omicron Subvariants

Area of Science:

• Virology
• Molecular Biology
• Biophysics

Background:

• The SARS-CoV-2 Omicron variant has rapidly evolved, accumulating mutations in its spike (S) protein.
• These mutations contribute to increased transmissibility and immune evasion, posing a global health challenge.
• While Omicron S protein binding affinity to host ACE2 is known, its binding stoichiometry remains unclear.

Purpose of the Study:

• To investigate the binding stoichiometry between different Omicron SARS-CoV-2 S protein subvariants and the human ACE2 receptor.
• To understand how S protein mutations impact ACE2 engagement beyond simple binding affinity.

Main Methods:

• Utilized mass photometry (MP) to precisely measure the stoichiometry of ACE2 binding to various Omicron S subvariants.
• MP allows for direct observation and quantification of molecular complexes.

Main Results:

• Mass photometry revealed diverse binding stoichiometries across different Omicron S subvariants.
• Observed stoichiometries indicate that mutations within the S protein actively modulate ACE2 engagement.
• Findings suggest ACE2 engagement is influenced by factors beyond just binding affinity.

Conclusions:

• The evolutionary path of ACE2 engagement among Omicron subvariants is nonlinear.
• Binding stoichiometry is a critical factor in the viral adaptation of SARS-CoV-2 Omicron subvariants.
• Understanding stoichiometry provides new insights into viral infectivity and evolution.