Molnupiravir is an orally available antiviral drug candidate currently in phase III trials for the treatment of patients with COVID-19. Molnupiravir increases the frequency of viral RNA mutations and impairs SARS-CoV-2 replication in animal models and in humans. Here, we establish the molecular mechanisms underlying molnupiravir-induced RNA mutagenesis by the viral RNA-dependent RNA polymerase (RdRp). Biochemical assays show that the RdRp uses the active form of molnupiravir, β-d-N4-hydroxycytidine (NHC) triphosphate, as a substrate instead of cytidine triphosphate or uridine triphosphate. When the RdRp uses the resulting RNA as a template, NHC directs incorporation of either G or A, leading to mutated RNA products. Structural analysis of RdRp–RNA complexes that contain mutagenesis products shows that NHC can form stable base pairs with either G or A in the RdRp active center, explaining how the polymerase escapes proofreading and synthesizes mutated RNA. This two-step mutagenesis mechanism probably applies to various viral polymerases and can explain the broad-spectrum antiviral activity of molnupiravir.
In this study, the carbamate structure of pseudoirreversible butyrylcholinesterase (BChE) inhibitors was optimized with regard to a longer binding to the enzyme. A set of compounds bearing different heterocycles (e.g., morpholine, tetrahydroisoquinoline, benzimidazole, piperidine) and alkylene spacers (2 to 10 methylene groups between carbamate and heterocycle) in the carbamate residue was synthesized and characterized in vitro for their binding affinity, binding kinetics, and carbamate hydrolysis. These novel BChE inhibitors are highly selective for hBChE over human acetycholinesterase (hAChE), yielding short-, medium-, and long-acting nanomolar hBChE inhibitors (with a halflife of the carbamoylated enzyme ranging from 1 to 28 h). The inhibitors show neuroprotective properties in a murine hippocampal cell line and a pharmacological mouse model of Alzheimer's disease (AD), suggesting a significant benefit of BChE inhibition for a disease-modifying treatment of AD.
The study of bacterial adhesion is crucial to our understanding of infection processes as well as for the development of antiadhesives. Here we have investigated new nanodiamond glycoconjugates intended to inhibit adhesion of type 1 fimbriated E. coli bacteria. For conjugation of saccharides and nanodiamond, thiourea‐bridging was employed, a method that has not been used before in nanodiamond derivatization. Amino‐prefunctionalized diamond nanoparticles were prepared employing aromatic diazonium salts and reacted with different isothiocyanato‐functionalized mannose derivatives. The resulting glyconanodiamonds were characterized and then tested in bacterial binding assays. They are recognized by the bacterial protein FimH according to the structure‐activity relationships known for this lectin. Thus, owing to the particular properties of nanodiamond, a valuable material is introduced with the potential to control bacterial adhesion and colonization in a favorable way.
Deoxyribozymes are emerging as modification‐specific endonucleases for the analysis of epigenetic RNA modifications. Here, we report RNA‐cleaving deoxyribozymes that differentially respond to the presence of natural methylated cytidines, 3‐methylcytidine (m3C), N4‐methylcytidine (m4C), and 5‐methylcytidine (m5C), respectively. Using in vitro selection, we found several DNA catalysts, which are selectively activated by only one of the three cytidine isomers, and display 10‐ to 30‐fold accelerated cleavage of their target m3C‐, m4C‐ or m5C‐modified RNA. An additional deoxyribozyme is strongly inhibited by any of the three methylcytidines, but effectively cleaves unmodified RNA. The mXC‐detecting deoxyribozymes are programmable for the interrogation of natural RNAs of interest, as demonstrated for human mitochondrial tRNAs containing known m3C and m5C sites. The results underline the potential of synthetic functional DNA to shape highly selective active sites.
RNA-cleaving deoxyribozymes can serve as selective sensors and catalysts to examine the modification state of RNA. However,s ite-specific endonuclease deoxyribozymes that selectively cleave post-transcriptionally modified RNAare extremely rare and their specificity over unmodified RNAi s low.W ereport that the native tRNAmodification N 6-isopentenyladenosine (i 6 A) strongly enhances the specificity and has the power to reconfigure the active site of an RNA-cleaving deoxyribozyme.Using in vitro selection, we identified aDNA enzyme that cleaves i 6 A-modified RNAatleast 2500-fold faster than unmodified RNA. Another deoxyribozyme shows unique and unprecedented behaviour by shifting its cleavage site in the presence of the i 6 AR NA modification. Together with deoxyribozymes that are strongly inhibited by i 6 A, these results highlight that post-transcriptional RNAm odifications modulate the catalytic activity of DNAi nvarious intricate ways.
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