Structure-based stabilization of non-native protein-protein interactions of coronavirus nucleocapsid proteins in antiviral drug design

Structure-based stabilization of protein-protein interactions (PPIs) is a promising strategy for drug discovery. However, this approach has mainly focused on the stabilization of native PPIs and non-native PPIs have received little consideration. Here, we identified a non-native interaction interface on the 3D dimeric structure of the N-terminal domain of the MERS-CoV nucleocapsid protein (MERS-CoV N-NTD). The interface formed a conserved hydrophobic cavity suitable for targeted drug screening. By considering the hydrophobic complementarity during the virtual screening step, we identified 5-benzyloxygramine as a new N protein PPI orthosteric stabilizer that possesses both antiviral and N-NTD protein-stabilizing activity. X-ray crystallography and small-angle X-ray scattering showed that 5-benzyloxygramine stabilizes the N-NTD dimers through simultaneous hydrophobic interactions to both partners, resulting in abnormal N protein oligomerization that was further confirmed in the cell. This unique approach based on the identification and stabilization of non-native PPIs of N protein could be applied towards drug discovery against CoV diseases.