Heme binding to the SARS-CoV-2 spike glycoprotein

Area of Science:

• Virology
• Immunology
• Biochemistry

Background:

• The SARS-CoV-2 spike glycoprotein is a key target for vaccine development and humoral immunity.
• Previous studies showed the spike N-terminal domain (NTD) binds biliverdin, affecting neutralizing antibodies.
• Heme is a product of heme catabolism.

Purpose of the Study:

• To investigate the interaction between SARS-CoV-2 spike glycoprotein and heme.
• To determine the binding affinity and location of heme on the spike protein.
• To explore the functional consequences of heme binding and potential catalytic activity.

Main Methods:

• Molecular modeling to predict heme binding site.
• Biochemical assays to determine heme binding affinity (K_D).
• Site-directed mutagenesis to confirm the binding pocket.
• Oxidation experiments with ascorbate to assess catalytic activity.

Main Results:

• SARS-CoV-2 spike glycoprotein binds heme with a K_D of 0.5 ± 0.2 μM.
• Molecular modeling identified a pocket in the NTD, lined by hydrophobic residues, as the heme binding site.
• Mutagenesis of N121 significantly reduced heme binding affinity, confirming the pocket's importance.
• The spike glycoprotein demonstrated catalytic activity, slowly converting heme to biliverdin in the presence of ascorbate.

Conclusions:

• The SARS-CoV-2 spike protein binds heme in a specific pocket within the NTD.
• This heme-binding capability, along with its oxidation activity, may be a viral mechanism to reduce free heme levels.
• Such activity could facilitate immune evasion by modulating host immune responses during infection.