ABSTRACT
Zinc deficiency is linked to poor prognosis in COVID-19 patients while clinical trials with zinc demonstrate better clinical outcomes. The molecular targets and mechanistic details of the anti-coronaviral activity of zinc remain obscure. We show that zinc not only inhibits the SARS-CoV-2 main protease (Mpro) with nanomolar affinity, but also viral replication. We present the first crystal structure of the Mpro-Zn2+ complex at 1.9 Å and provide the structural basis of viral replication inhibition. We show that Zn2+ coordinates with the catalytic dyad at the enzyme active site along with two previously unknown water molecules in a tetrahedral geometry to form a stable inhibited Mpro-Zn2+ complex. Further, the natural ionophore quercetin increases the anti-viral potency of Zn2+. As the catalytic dyad is highly conserved across SARS-CoV, MERS-CoV and all variants of SARS-CoV-2, Zn2+ mediated inhibition of Mpro may have wider implications.
Subject(s)
Coronavirus 3C Proteases/antagonists & inhibitors , Protease Inhibitors/chemistry , SARS-CoV-2/enzymology , Zinc/chemistry , Animals , Binding Sites , COVID-19/pathology , Catalytic Domain , Chlorocebus aethiops , Coordination Complexes/chemistry , Coordination Complexes/metabolism , Coronavirus 3C Proteases/metabolism , Crystallography, X-Ray , Humans , Ions/chemistry , Kinetics , Molecular Dynamics Simulation , Protease Inhibitors/metabolism , Protease Inhibitors/pharmacology , SARS-CoV-2/isolation & purification , Surface Plasmon Resonance , Thermodynamics , Vero Cells , Virus Replication/drug effectsABSTRACT
Acinetobacter baumannii is an opportunistic Gram-negative bacterial pathogen, associated mostly with hospital-acquired infections. The emergence of drug resistance strains made it necessary to explore new pathways for the development of more effective antibiotics. Enoyl CoA reductase (FabI), a key enzyme in the fatty acid biosynthesis (FAS) pathway, has emerged as a potential target for antibacterial drug development. Earlier reports show that the lead SaFabI inhibitor AFN-1252 can inhibit FabI from other organisms including Escherichia coli and Burkholderia pseudomallei, but with differential potency. In the present work, we show that AFN-1252 is a moderate inhibitor of AbFabI with an IC50 of 216 nM. AFN-1252 stabilized AbFabI with a 4.2°C increase in the melting temperature (Tm ) and, interestingly, the stabilization effect was significantly increased in presence of the cofactor NADH (∆Tm = 17°C), suggesting the formation of a ternary complex AbFabI: AFN-1252: NADH. X-ray crystallography studies of AbFabI co-crystalized with AFN-1252 and NADH confirmed the ternary complex formation. The critical interactions of AFN-1252 with AbFabI and NADH identified from the co-crystal structure may facilitate the design and development of new drugs against A. baumannii infections by targeting the FAS pathway.
