Computational investigation of binding of chloroquinone and hydroxychloroquinone against PLPro of SARS-CoV-2

Novel coronavirus SARS-CoV-2 has infected 18 million people with 700,000+ mortalities worldwide and this deadly numeric figure is rapidly rising. With very few success stories, the therapeutic targeting of this epidemic has been mainly attributed to main protease (Mpro), whilst Papain-like proteases (PLpro) also plays a vital role in the processing of replicase polyprotein. Multifunctional roles of PLpro such as viral polypeptide cleavage, de-ISGlyation and immune suppression have made it a promising drug target for therapeutic interventions. Whilst there have been a number of studies and others are on-going on repurposing and new-small molecule screening, albeit previously FDA approved drugs viz. Chloroquine (CQ) and Hydroxychloroquine (HCQ) have only been found effective against this pandemic. Inspired by this fact, we have carried out molecular docking and dynamics simulation studies of FDA approved CQ and HCQ against SARS-CoV-2 PLpro. The end aim is to characterise the binding mode of CQ and HCQ and identify the key amino acid residues involved in the mechanism of action. Further, molecular dynamics simulations (MDS) were carried out with the docked complex to search for the conformational space and for understanding the integrity of binding mode. We showed that the CQ and HCQ can bind with better binding affinity with PLpro as compared to reference known PLpro inhibitor. Based on the presented findings, it can be anticipated that the SARS-CoV-2 PLpro may act as molecular target of CQ and HCQ, and can be projected for further exploration to design potent inhibitors of SARS-CoV-2 PLpro in the near future.