A Fungal Defensin Targets the SARS-CoV-2 Spike Receptor-Binding Domain

Area of Science:

• Biochemistry
• Structural Biology
• Antimicrobial Peptides

Background:

• Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) causes COVID-19, necessitating new targeted therapies.
• Viral entry into host cells is mediated by the Spike protein's receptor-binding domain (RBD) interacting with ACE2.
• Developing high-affinity RBD binders is a promising strategy to inhibit viral entry.

Purpose of the Study:

• To discover and improve high-affinity binders targeting the SARS-CoV-2 RBD.
• To explore fungal defensins as a potential source for antiviral agents.
• To investigate the binding mechanism of micasin to the SARS-CoV-2 RBD.

Main Methods:

• Computational modeling to predict binding interactions.
• Experimental validation using microscale thermophoresis (MST) to assess binding affinity.
• Protein engineering (single point mutation) to enhance binding affinity.

Main Results:

• Micasin, a fungal defensin, demonstrated binding to the SARS-CoV-2 RBD via shape complementarity and hydrophobic/hydrogen-bonding interactions.
• Micasin and its derivative showed low micromolar affinity for RBD.
• A single point mutation in micasin increased the interface area and hydrogen bond network, enhancing binding affinity six-fold.

Conclusions:

• Naturally occurring fungal defensins, like micasin, represent a promising resource for developing novel antiviral agents against SARS-CoV-2.
• Targeting the RBD-ACE2 interaction with improved micasin derivatives could lead to effective therapeutics for COVID-19.
• Structure-based design and experimental validation are effective for optimizing natural compounds into potent antiviral agents.