Peptidomimetic Analogues Act as Effective Inhibitors against SARS-CoV-2 by Blocking the Function of Cathepsin L.

Cathepsin L (CatL) is a promising antiviral drug target of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as an important protease for cleaving the SARS-CoV-2 spike protein and enhancing viral entry to cells. We identified a tripeptide aldehyde candidate, D1-1, which exhibited inhibitory effects against SARS-CoV-2 in Vero E6 cells. The protease screening analysis and protein pull-down assays demonstrated the direct binding of D1-1 to CatL. Guided by molecular docking, we synthesized 72 analogues. Upon analyzing the structure-activity relationships of these inhibitors, the D6 series was developed. Among them, D6-3 functioned as the most potent CatL inhibitor (IC50 = 0.27 nM, EC50 = 0.26 µM). D6-3 effectively blocked the CatL function and substantially hindered the entry of the SARS-CoV-2 pseudovirus to cells. Our work presented novel compounds for targeting and inhibiting CatL, offering valuable insights into the development of SARS-CoV-2 antivirals.

The structure-based design of peptidomimetic inhibitors against SARS-CoV-2 3C like protease as Potent anti-viral drug candidate.

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), as the pathogen of coronavirus disease 2019 (COVID-19), has infected millions of people and took hundreds of thousands of lives. Unfortunately, there is deficiency of effective medicines to prevent or treat COVID-19. 3C like protease (3CLPro) of SARS-CoV-2 is essential to the viral replication and transcription, and is an attractive target to develop anti-SARS-CoV-2 agents. Targeting on the 3CLPro, we screened our protease inhibitor library and obtained compound 10a as hit to weakly inhibit the SARS-CoV-2 3CLPro, and determined the co-crystal structure of 10a and the protease. Based on the deep understanding on the protein-ligand complexes between the hit and SARS-CoV-2 3CLPro, we designed a series of peptidomimetic inhibitors, with outstanding inhibitory activity against SARS-CoV-2 3CLPro and excellent anti-viral potency against SARS-CoV-2. The protein-ligand complexes of the other key inhibitors with SARS-CoV-2 3CLPro were explicitly described by the X-ray co-crystal study. All such results suggest these peptidomimetic inhibitors could be further applied as encouraging drug candidates.

Comprehensive Insights into the Catalytic Mechanism of Middle East Respiratory Syndrome 3C-Like Protease and Severe Acute Respiratory Syndrome 3C-Like Protease.

Coronavirus 3C-like protease (3CLPro) is a highly conserved cysteine protease employing a catalytic dyad for its functions. 3CLPro is essential to the viral life cycle and, therefore, is an attractive target for developing antiviral agents. However, the detailed catalytic mechanism of coronavirus 3CLPro remains largely unknown. We took an integrated approach of employing X-ray crystallography, mutational studies, enzyme kinetics study, and inhibitors to gain insights into the mechanism. Such experimental work is supplemented by computational studies, including the prereaction state analysis, the ab initio calculation of the critical catalytic step, and the molecular dynamic simulation of the wild-type and mutant enzymes. Taken together, such studies allowed us to identify a residue pair (Glu-His) and a conserved His as critical for binding; a conserved GSCGS motif as important for the start of catalysis, a partial negative charge cluster (PNCC) formed by Arg-Tyr-Asp as essential for catalysis, and a conserved water molecule mediating the remote interaction between PNCC and catalytic dyad. The data collected and our insights into the detailed mechanism have allowed us to achieve a good understanding of the difference in catalytic efficiency between 3CLPro from SARS and MERS, conduct mutational studies to improve the catalytic activity by 8-fold, optimize existing inhibitors to improve the potency by 4-fold, and identify a potential allosteric site for inhibitor design. All such results reinforce each other to support the overall catalytic mechanism proposed herein.

Crystal Structure of African Swine Fever Virus pS273R Protease and Implications for Inhibitor Design.

African swine fever (ASF) is a highly contagious hemorrhagic viral disease of domestic and wild pigs that is responsible for serious economic and production losses. It is caused by the African swine fever virus (ASFV), a large and complex icosahedral DNA virus of the Asfarviridae family. Currently, there is no effective treatment or approved vaccine against the ASFV. pS273R, a specific SUMO-1 cysteine protease, catalyzes the maturation of the pp220 and pp62 polyprotein precursors into core-shell proteins. Here, we present the crystal structure of the ASFV pS273R protease at a resolution of 2.3 Å. The overall structure of the pS273R protease is represented by two domains named the "core domain" and the N-terminal "arm domain." The "arm domain" contains the residues from M1 to N83, and the "core domain" contains the residues from N84 to A273. A structure analysis reveals that the "core domain" shares a high degree of structural similarity with chlamydial deubiquitinating enzyme, sentrin-specific protease, and adenovirus protease, while the "arm domain" is unique to ASFV. Further, experiments indicated that the "arm domain" plays an important role in maintaining the enzyme activity of ASFV pS273R. Moreover, based on the structural information of pS273R, we designed and synthesized several peptidomimetic aldehyde compounds at a submolar 50% inhibitory concentration, which paves the way for the design of inhibitors to target this severe pathogen.IMPORTANCE African swine fever virus, a large and complex icosahedral DNA virus, causes a deadly infection in domestic pigs. In addition to Africa and Europe, countries in Asia, including China, Vietnam, and Mongolia, were negatively affected by the hazards posed by ASFV outbreaks in 2018 and 2019, at which time more than 30 million pigs were culled. Until now, there has been no vaccine for protection against ASFV infection or effective treatments to cure ASF. Here, we solved the high-resolution crystal structure of the ASFV pS273R protease. The pS273R protease has a two-domain structure that distinguishes it from other members of the SUMO protease family, while the unique "arm domain" has been proven to be essential for its hydrolytic activity. Moreover, the peptidomimetic aldehyde compounds designed to target the substrate binding pocket exert prominent inhibitory effects and can thus be used in a potential lead for anti-ASFV drug development.