An intrinsic loop-mediated structural stability modulating inhibitor potency in the SADS-CoV and SARS-CoV-2 main...

Area of Science:

• Virology
• Structural Biology
• Drug Discovery

Background:

• Swine acute diarrhea syndrome coronavirus (SADS-CoV) presents a substantial zoonotic threat.
• The lack of SADS-CoV main protease (Mpro) structural data hinders antiviral drug development.

Purpose of the Study:

• To elucidate the high-resolution structures of SADS-CoV Mpro and its complexes with inhibitors.
• To understand the novel inhibition mechanism and structural basis for inhibitor potency.

Main Methods:

• X-ray crystallography was used to determine the structures of SADS-CoV Mpro and its inhibitor complexes.
• Cell-based assays and porcine intestinal organoids were employed to assess antiviral activity.

Main Results:

• High-resolution structures of SADS-CoV Mpro with inhibitors 27h and SY110 were obtained, revealing a unique single-helix conformation (residues 40-53).
• This differs from the coiled-coil structure in SARS-CoV-2 Mpro, impacting inhibitor potency.
• Inhibitor 27h demonstrated efficient suppression of SADS-CoV replication in vitro and in organoids.

Conclusions:

• Intrinsic Mpro dynamics significantly influence inhibitor potency.
• The absence of residue '51' in Alphacoronavirus Mpros is crucial for observed conformational changes.
• Findings provide a basis for designing broad-spectrum Mpro inhibitors against coronaviruses.