![]() The 2′,3′-cyclic phosphodiester is then hydrolyzed to 3′-phosphomonoester. It was reported that NendoU cleaves both single- and double-stranded RNA at uridine sites producing 2′,3′-cyclic phosphodiester and 5′-hydroxyl termini 2. The Nsp15 enzyme is active as a 234 kDa hexamer consisting of three dimers. The viral EndoU subfamily has been named NendoU. They are involved in RNA processing and broadly distributed in viruses, archaea, bacteria, plants, humans, and other animals. Its catalytic C-terminal domain shows sequence similarity and functionality of the EndoU family enzymes. ![]() Nsp15 is a uridine-specific endoribonuclease. Non-structural proteins are potential drug targets for therapies and, because of their essentiality, sequence, and function conservation, developed therapeutics might in principle inhibit all human coronaviruses. In addition, several sub-genomic RNAs are generated from (-) sense RNA during virus proliferation, resulting in translation of 4 structural and 9-10 accessory proteins. For CoV-2 the cleavage yields 15 Nsps, (Nsp11 is just a 7-residues peptide) that assemble into a large membrane-bound RTC that exhibits multiple enzymatic and binding activities. These polypeptides are processed by two viral proteases: papain-like protease (PLpro, a domain within non-structural protein 3 (Nsp3)), and 3C-like protease (Nsp5 or 3CLpro or Mpro). These genomes are used as mRNA for translation of a replicase-transcriptase complex (RTC) constituents made of two large polyproteins, Pp1a and Pp1ab, and as a template for replication of its own copy 1. Since February 2020, concerted efforts have focused on characterizing its biology and developing various detection and treatment options, ranging from vaccines through antibodies to antivirals.Īs a typical member of the Coronaviridae family, it is spherical, enveloped, non-segmented, (+) sense RNA virus with a large ~30 kbs genome. At the time of writing, there is no vaccine or proven drug against SARS-CoV-2. The current pandemic of COVID-19 is caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Our findings provide new insights for the development of uracil scaffold-based drugs. Using crystallography, biochemical, and whole-cell assays, we demonstrate that Tipiracil inhibits SARS-CoV-2 Nsp15 by interacting with the uridine binding pocket in the enzyme’s active site. ![]() This acquired knowledge was instrumental in identifying Tipiracil, an FDA approved drug that is used in the treatment of colorectal cancer, as a potential anti-COVID-19 drug. In the presence of manganese ions, the enzyme cleaves unpaired RNAs. The structure with a transition state analog, uridine vanadate, confirms interactions key to catalytic mechanisms. In addition to a uridine site we present evidence for a second base binding site that can accommodate any base. Here we report the first structures with bound nucleotides and show how the enzyme specifically recognizes uridine moiety. As endoribonuclease activity seems to be responsible for the interference with the innate immune response, Nsp15 emerges as an attractive target for therapeutic intervention. ![]() ![]() SARS-CoV-2 Nsp15 is a uridine-specific endoribonuclease with C-terminal catalytic domain belonging to the EndoU family that is highly conserved in coronaviruses. ![]()
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