Two Binding Sites of SARS-CoV-2 Macrodomain 3 Probed by Oxaprozin and Meclomen.

Severe acute respiratory syndrome-coronavirus-1/2 (SARS-CoV-1/2) macrodomain 3 (Mac3) is critical for replication and transcription of the viral genome and is therefore a potential therapeutic target. Here, we solved the crystal structure of SARS-CoV-2 Mac3, which reveals a small-molecule binding pocket. Two low-molecular-weight drugs, oxaprozin and meclomen, induced different patterns of nuclear magnetic resonance (NMR) chemical shift perturbations (CSPs). Meclomen binds to site I of SARS-CoV-2 Mac3 with binding pose determined by NMR CSP and transferred paramagnetic relaxation enhancement, while oxaprozin binds to site II as revealed by the crystal structure. Interestingly, oxaprozin and meclomen both perturb residues in site I of SARS-CoV Mac3. Fluorescence polarization experiments further demonstrated that oxaprozin and meclomen inhibited the binding of DNA-G4s to SARS-CoV-2 Mac3. Our work identified two adjacent ligand-binding sites of SARS-CoV-2 Mac3 that shall facilitate structure-guided fragment linking of these compounds for more potent inhibitors.

Repurposing Low-Molecular-Weight Drugs against the Main Protease of Severe Acute Respiratory Syndrome Coronavirus 2.

The coronavirus disease pandemic caused by infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has affected the global healthcare system. As low-molecular-weight drugs have high potential to completely match interactions with essential SARS-CoV-2 targets, we propose a strategy to identify such drugs using the fragment-based approach. Herein, using ligand- and protein-observed fragment screening approaches, we identified niacin and hit 1 binding to the catalytic pocket of the main protease (Mpro) of SARS-CoV-2, thereby modestly inhibiting the enzymatic activity of Mpro. We further searched for low-molecular-weight drugs containing niacin or hit 1 pharmacophores with enhanced inhibiting activity, e.g., carmofur, bendamustine, triclabendazole, emedastine, and omeprazole, in which omeprazole is the only one binding to the C-terminal domain of SARS-CoV-2 Mpro. Our study demonstrates that the fragment-based approach is a feasible strategy for identifying low-molecular-weight drugs against the SARS-CoV-2 and other potential targets lacking specific drugs.