Detailed Insights into the Inhibitory Mechanism of New Ebselen Derivatives against Main Protease (Mpro) of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2).

SARS-CoV-2 main protease (Mpro/3CLpro) is a crucial target for therapeutics, which is responsible for viral polyprotein cleavage and plays a vital role in virus replication and survival. Recent studies suggest that 2-phenylbenzisoselenazol-3(2H)-one (ebselen) is a potent covalent inhibitor of Mpro, which affects its enzymatic activity and virus survival. Herein, we synthesized various ebselen derivatives to understand the mechanism of Mpro inhibition by ebselen. Using ebselen derivatives, we characterized the detailed interaction mechanism with Mpro. We discovered that modification of the parent ebselen inhibitor with an electron-withdrawing group (NO2) increases the inhibition efficacy by 2-fold. We also solved the structure of an Mpro complex with an ebselen derivative showing the mechanism of inhibition by blocking the catalytic Cys145 of Mpro. Using a combination of crystal structures and LC-MS data, we showed that Mpro hydrolyzes the new ebselen derivative and leaves behind selenium (Se) bound with Cys145 of the catalytic dyad of Mpro. We also described the binding profile of ebselen-based inhibitors using molecular modeling predictions supported by binding and inhibition assays. Furthermore, we have also solved the crystal structure of catalytically inactive mutant H41N-Mpro, which represents the inactive state of the protein where the substrate binding pocket is blocked. The inhibited structure of H41N-Mpro shows gatekeeper residues in the substrate binding pocket responsible for blocking the substrate binding; mutation of these gatekeeper residues leads to hyperactive Mpro.

Comparative transcriptome profiling reveals the basis of differential sheath blight disease response in tolerant and susceptible rice genotypes.

Rice sheath blight (ShB) disease, caused by the fungal pathogen Rhizoctonia solani AG1-IA, is one of the devastating diseases and causes severe yield losses all over the world. No completely resistant germplasm is known till now, and as a result, the progress in resistance breeding is unsatisfactory. Basic studies to identify candidate genes, QTLs, and to better understand the host-pathogen interaction are also scanty. In this study, we report the identification of a new ShB-tolerant rice germplasm, CR 1014. Further, we investigated the basis of tolerance by exploring the disease responsive differentially expressed transcriptome and comparing them with that of a susceptible variety, Swarna-Sub1. A total of 815 and 551 genes were found to be differentially regulated in CR 1014 and Swarna-Sub1, respectively, at two different time points. The result shows that the ability to upregulate genes for glycosyl hydrolase, secondary metabolite biosynthesis, cytoskeleton and membrane integrity, the glycolytic pathway, and maintaining photosynthesis make CR 1014 a superior performer in resisting the ShB pathogen. We discuss several putative candidate genes for ShB resistance. The present study, for the first time, revealed the basis of ShB tolerance in the germplasm CR1014 and should prove to be particularly valuable in understanding molecular response to ShB infection. The knowledge could be utilized to devise strategies to manage the disease better.