Insect protease inhibitors; promising inhibitory compounds against SARS-CoV-2 main protease.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has adversely affected global health since its emergence in 2019. The lack of effective treatments prompted worldwide efforts to immediately develop therapeutic strategies against COVID-19. The main protease (M(pro)) of SARS-CoV-2 plays a crucial role in viral replication, and therefore it serves as an attractive target for COVID-19-specific drug development. Due to the richness and diversity of insect protease inhibitors, we docked SARS-CoV-2 M(pro) onto 25 publicly accessible insect-derived protease inhibitors using the ClusPro server, and the regions with high inhibitory potentials against M(pro) were used to design peptides. Interactions of these inhibitory peptides with M(pro) were further assessed by two directed docking programs, AutoDock and Haddock. AutoDock analysis predicted the highest binding energy (-9.39 kcal/mol) and the lowest inhibition constant (130 nM) for the peptide 1KJ0-7 derived from SGCI (Schistocerca gregaria chymotrypsin inhibitor). On the other hand, Haddock analysis resulted in the discovery of a different peptide designated 2ERW-9 from infestin, a serine protease inhibitor of Triatoma infestans, with the best docking score (-131), binding energy (-11.7 kcal/mol), and dissociation constant (2.6E-09 M) for M(pro). Furthermore, using molecular dynamic simulations, 1KJ0-7 and 2ERW-9 were demonstrated to form stable complexes with M(pro). The peptides also showed suitable drug-likeness properties compared to commercially available drugs based on Lipinski's rule. Our findings present two peptides with possible protease inhibitor activities against M(pro) and further demonstrate the potential of insect-derived peptides and computer-aided methods for drug discovery.