- GC376 forms a covalent bond with the active site residue Cys145, and can directly block activity of the main protease, which plays a key role of viral infection in the host cell. It was found that GC376 was stabilized in the active site of the main protease of SARS-CoV-2 by multiple hydrophobic and hydrophilic interactions.

GC376 active site bond location for the main protease of SARS-CoV-2

- The Kd value of GC376 to the main protease of SARS-CoV-2 is 1.6uM. This value was determined by isothermal titration calorimetry.

Santa Clara University

Wang and colleagues used differential scanning fluorimetry to look at the binding affinity of GC376 and other main protease inhibitors to SARS-CoV-2.

Study Investigating the Effectiveness of GC376 as a Coronaviral Protease Inhibitor

The Kd is the binding constant, a unit of measurement that demonstrates how tightly a ligand binds to a protein. The lower the Kd value, the tighter the bond is between the ligand and the protein. 

What is Kd?

Wang, Y., Yang W., Chen Y. et al.(2020 Aug 1). Structural basis of SARS-CoV-2 main protease inhibition by a broad spectrum anti-coronaviral drug. American Journal of Cancer Research, 10(8): 2535-2545. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7471349/pdf/ajcr0010-2535.pdf	


Structural basis of SARS-CoV-2 main protease inhibition by a broad spectrum anti-coronaviral drug 

- Studies have demonstrated the ability of GC376 to prevent the proliferation of multiple human and animal coronaviruses.

The coronaviruses it has shown to prevent the proliferation of are:
- MERS-CoV
- SARS-CoV-1
- porcine epidemic diarrhea virus (PEDV)
- feline infectious peritonitis virus (FIPV)


GC376 Prevents the Proliferation of Multiple Coronaviruses

- To determine how effective GC376 is at inhibiting the activity of the main protease of SARS-CoV-2, a fluorescence resolution energy transfer assay with a fluorescence protein substrate was used. It was found that GC376 has a potent ability to inhibit the activity of SARS-CoV-2 main protease, with a half-maximal inhibitory concentration of 0.89uM. 

The inhibition efficiency of GC376 on SARS-CoV-2

The structure of the main protease of SARS-CoV-2 was found to be very similar to the main protease of SARS-CoV-1. The two proteases share 96.08% sequence identity. 


Structural Analysis of the Main Protease of SARS-CoV-2

The structure of the main proteases of the coronaviruses from this study were all very similar. Wang and colleagues suggest that GC376 may be very adaptable to inhibit the main proteases of all coronaviruses since the structures of their main proteases are very similar. 

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