Porcine epidemic diarrhea virus papain-like protease 2 can be noncompetitively inhibited by 6-thioguanine.

Porcine epidemic diarrhea virus (PEDV) is a coronavirus (CoV) discovered in the 1970s that infects the intestinal tract of pigs, resulting in diarrhea and vomiting. It can cause extreme dehydration and death in neonatal piglets. In Asia, modified live attenuated vaccines have been used to control PEDV infection in recent years. However, a new strain of PEDV that belongs to genogroup 2a appeared in the USA in 2013 and then quickly spread to Canada and Mexico as well as Asian and European countries. Due to the less effective protective immunity provided by the vaccines against this new strain, it has caused considerable agricultural and economic loss worldwide. The emergence of this new strain increases the importance of understanding PEDV as well as strategies for inhibiting it. Coronaviral proteases, including main proteases and papain-like proteases, are ideal antiviral targets because of their essential roles in viral maturation. Here we provide a first description of the expression, purification and structural characteristics of recombinant PEDV papain-like protease 2, moreover present our finding that 6-thioguanine, a chemotherapeutic drug, in contrast to its competitive inhibition on SARS- and MERS-CoV papain-like proteases, is a noncompetitive inhibitor of PEDV papain-like protease 2.

Disulfiram can inhibit MERS and SARS coronavirus papain-like proteases via different modes.

Severe acute respiratory syndrome coronavirus (SARS-CoV) emerged in southern China in late 2002 and caused a global outbreak with a fatality rate around 10% in 2003. Ten years later, a second highly pathogenic human CoV, MERS-CoV, emerged in the Middle East and has spread to other countries in Europe, North Africa, North America and Asia. As of November 2017, MERS-CoV had infected at least 2102 people with a fatality rate of about 35% globally, and hence there is an urgent need to identify antiviral drugs that are active against MERS-CoV. Here we show that a clinically available alcohol-aversive drug, disulfiram, can inhibit the papain-like proteases (PLpros) of MERS-CoV and SARS-CoV. Our findings suggest that disulfiram acts as an allosteric inhibitor of MERS-CoV PLpro but as a competitive (or mixed) inhibitor of SARS-CoV PLpro. The phenomenon of slow-binding inhibition and the irrecoverability of enzyme activity after removing unbound disulfiram indicate covalent inactivation of SARS-CoV PLpro by disulfiram, while synergistic inhibition of MERS-CoV PLpro by disulfiram and 6-thioguanine or mycophenolic acid implies the potential for combination treatments using these three clinically available drugs.