Amphibian-Derived Peptides as Natural Inhibitors of SARS-CoV-2 Main Protease (M^pro): A Combined In Vitro and In...

The COVID-19 pandemic, caused by the SARS-CoV-2 virus, has highlighted the urgent need for novel therapeutic agents targeting viral enzymes such as the main protease (M^pro), which plays a crucial role in viral replication. In this study, we investigate the inhibitory potential of 23 peptides isolated from the skin of amphibians belonging to the Hylidae and Leptodactylidae families against SARS-CoV-2 M^pro. Five peptides demonstrated significant inhibition using a colorimetric M^pro inhibition assay, with IC₅₀ values ranging from 41 to 203 µM. Among these, peptides Hp-1081 and Hp-1971, derived from Boana pulchella, exhibited the strongest activity, comparable to the natural M^pro inhibitor quercetin. The binding mechanism of the most potent peptide, Hp-1081, was further investigated through docking and molecular dynamics (MDs) simulations and energetic analysis, which revealed key M^pro residues involved in the binding process. Moreover, because SARS-CoV-2 infection can induce ROS overproduction, the antioxidant activity of Hp-1081 was assessed, reaching 48% of DPPH radical scavenging activity at 100 µM. The most potent peptides also showed no toxicity against human erythrocytes and Artemia salina. This study provides insight into the antiviral potential of amphibian-derived peptides and highlights their applicability as natural templates for drug development targeting coronaviruses.