In recent history, coronaviruses have proven to be a very serious threat to the human population. Severe acute respiratory syndrome (SARS) coronavirus and the Middle East respiratory syndrome (MERS) coronavirus emerged in 2003 and 2012, respectively. We are currently witnessing a new outbreak caused by the highly pathogenic SARS-coronavirus-2 (SARS-CoV-2) that spread from China all over the world causing serious respiratory disease in humans (COVID-19) with a high mortality rate. All three coronaviruses probably originated in bats and were transmitted to humans. Currently, there are no vaccines or drugs that can treat any zoonotic coronavirus and they are a permanent threat to public health.In the framework of this project, we will try to disable the mechanism that coronaviruses have evolved to manipulate the host antiviral response to their advantage. Our focus will be on a posttranslational modification, i.e., ADP-ribosylation, that plays an important role in antiviral response and innate immunity. Antiviral PARP activity (transfer of ADP-ribose onto different target proteins) leads to the induction of interferon response (a central part of the innate immune system) and inhibition of virus replication. A key role in the regulation of ADP-ribosylation play evolutionarily conserved protein domains called macrodomains which can remove ADP-ribose from modified proteins. All coronaviruses contain such a macrodomain as a part of their non-structural protein 3 (Nsp3) and use them to neutralize effects of antiviral ADP-ribosylation. Coronavirus macrodomains have been shown to be essential for viral pathogenesis they promote virus replication and suppress interferon response, and as such are promising antiviral drug targets. Inhibition of coronaviruses' macrodomains using small molecules has become a novel therapeutic approach for treating coronavirus-induced disease.The aim of our project is to find coronavirus-specific macrodomain inhibitors with the potential to interfere with SARS-CoV-2 macrodomain activities. First, we will perform virtual screening of FDA-approved and commercial small compound libraries to select potential SARS-CoV-2 macrodomain inhibitors. Next, the inhibitory effect of selected compounds will be validated by testing the ability of the coronavirus macrodomain to hydrolyse different ADP-ribosylated substrates in inhibitor presence in vitro. Finally, the most promising inhibitor candidates will be subjected to in vivo testing using macrophage and mouse models. We hope that our research will result in a compound (or compounds) with the potential of becoming a drug for treating coronavirus-induced disease. Also, our results will contribute to the understanding of the mechanism which coronaviruses use through their macrodomains to promote virus replication and weaken the host immune system. Using the proposed computational and experimental analysis, we will obtain information necessary for designing novel, structure-based, and highly specific coronavirus macrodomain inhibitors. With this project, we will build and establish a streamlined pipeline for coronavirus macrodomain inhibitor discovery which together with our expertise could be mobilised anytime in the future to find/improve macrodomain inhibitors for potential new highly pathogenic coronaviruses.