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A distinct ssDNA/RNA binding interface in the Nsp9 protein from SARS-CoV-2.

ABSTRACT: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel, highly infectious RNA virus that belongs to the coronavirus family. Replication of the viral genome is a fundamental step in the virus life cycle and SARS-CoV-2 non-structural protein 9 (Nsp9) is shown to be essential for virus replication through its ability to bind RNA in the closely related SARS-CoV-1 strain. Two recent studies revealing the three-dimensional structure of Nsp9 from SARS-CoV-2 have demonstrated a high degree of similarity between Nsp9 proteins within the coronavirus family. However, the binding affinity to RNA is very low which, until now, has prevented the determination of the structural details of this interaction. In this study, we have utilized nuclear magnetic resonance spectroscopy (NMR) in combination with surface biolayer interferometry (BLI) to reveal a distinct binding interface for both ssDNA and RNA that is different to the one proposed in the recently solved SARS-CoV-2 replication and transcription complex (RTC) structure. Based on these data, we have proposed a structural model of a Nsp9-RNA complex, shedding light on the molecular details of these important interactions.

SUBMITTER: El-Kamand S

PROVIDER: S-EPMC8441931 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Nanobodies agains Sars Cov 2 Nsp9 protein protects cells from virus infection

Project description:Nanobodies are emerging as ideal instruments for drug design and several have recently been created to block SARS-Cov-2 entry in the host cell by targeting surface-exposed Spike protein. However, due to the high frequency of mutations that affect Spike, these nanobodies may not efficiently target Spike during viral entry. Here we have established a pipeline that instead targets highly conserved viral proteins that are made only after viral entry into the host cell when the SARS-Cov-2 RNA-based genome is translated. As proof of principle, we designed nanobodies against the SARS-CoV-2 non-structural protein Nsp9, required for replication of the viral genome. To find out if this strategy efficiently blocked viral replication, one of these anti-Nsp9 nanobodies, 2NSP23, previously characterized using immunoassays and NMR spectroscopy for epitope mapping, was encapsulated into lipid nanoparticles (LNP) as mRNA. We show that this nanobody, hereby referred to as LNP-mRNA-2NSP23, is internalized and translated in HEK293 cells. We next infected HEK293-ACE2 cells subjected to LNP-mRNA-2NSP23 with multiple SARS-CoV-2 variants. Analysis of total RNA isolated form infected cells treated or untreated with LNP-mRNA-2NSP23 using qPCR and RNA deep sequencing shows that the LNP-mRNA-2NSP23 nanobody protects HEK293-ACE2 cells and suppresses replication of several SARS-CoV-2 variants. These observations indicate that following translation, the nanobody 2NSP23 inhibits viral replication by targeting Nsp9 in living cells. We propose that LNP-mRNA-2NSP23 may be translated into an innovative technology to generate novel antiviral drugs highly efficient across coronaviruses.

2023-10-10 | GSE244714 | GEO

Binding Studies of the Prodrug HAO472 to SARS-Cov-2 Nsp9 and Variants.

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| S-EPMC8862745 | biostudies-literature

Crystal Structure of the SARS-CoV-2 Non-structural Protein 9, Nsp9.

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A natural product compound inhibits coronaviral replication in vitro by binding to the conserved Nsp9 SARS-CoV-2 protein.

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| S-EPMC8553373 | biostudies-literature

Structural basis for the multimerization of nonstructural protein nsp9 from SARS-CoV-2.

Project description:Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of a potentially fatal disease named coronavirus disease 2019 (COVID-19), has raised significant public health concerns globally. To date, the COVID-19 pandemic has caused millions of people to be infected with SARS-CoV-2 worldwide. It has been known since the 2003 SARS epidemic that coronaviruses (CoVs) have large RNA genomes, the replication of which requires an RNA-dependent RNA replication/transcription complex. CoV nonstructural proteins (Nsps) play pivotal roles in the assembly of this complex and associated enzymatic functions in virus genomic replication. Several smaller nonenzymatic Nsps assist with RNA-dependent RNA polymerase function. In this study, we determined the structure of SARS-CoV-2 nonstructural protein 9 (nsp9), an RNA-binding protein that is essential for CoV replication. Its homotetrameric structure with two stable dimeric interfaces provids a structural basis for understanding the mechanisms of RNA-binding protein self-assembly, which may be essential for the regulation of viral RNA replication and transcription.

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Discrimination against RNA Backbones by a ssDNA Binding Protein.

Project description:Pot1 is the shelterin component responsible for the protection of the single-stranded DNA (ssDNA) overhang at telomeres in nearly all eukaryotic organisms. The C-terminal domain of the DNA-binding domain, Pot1pC, exhibits non-specific ssDNA recognition, achieved through thermodynamically equivalent alternative binding conformations. Given this flexibility, it is unclear how specificity for ssDNA over RNA, an activity required for biological function, is achieved. Examination of the ribose-position specificity of Pot1pC shows that ssDNA specificity is additive but not uniformly distributed across the ligand. High-resolution structures of several Pot1pC complexes with RNA-DNA chimeric ligands reveal Pot1pC discriminates against RNA by utilizing non-compensatory binding modes that feature significant rearrangement of the binding interface. These alternative conformations, accessed through both ligand and protein flexibility, recover much, but not all, of the binding energy, leading to the observed reduction in affinities. These findings suggest that intermolecular interfaces are remarkably sophisticated in their tuning of specificity toward flexible ligands.

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Structural, energetic and lipophilic analysis of SARS-CoV-2 non-structural protein 9 (NSP9).

Project description:In SARS-CoV-2 replication complex, the Non-structural protein 9 (Nsp9) is an important RNA binding subunit in the RNA-synthesizing machinery. The dimeric forms of coronavirus Nsp9 increase their nucleic acid binding affinity and the N-finger motif appears to play a critical role in dimerization. Here, we present a structural, lipophilic and energetic study about the Nsp9 dimer of SARS-CoV-2 through computational methods that complement hydrophobicity scales of amino acids with molecular dynamics simulations. Additionally, we presented a virtual N-finger mutation to investigate whether this motif contributes to dimer stability. The results reveal for the native dimer that the N-finger contributes favorably through hydrogen bond interactions and two amino acids bellowing to the hydrophobic region, Leu45 and Leu106, are crucial in the formation of the cavity for potential drug binding. On the other hand, Gly100 and Gly104, are responsible for stabilizing the α-helices and making the dimer interface remain stable in both, native and mutant (without N-finger motif) systems. Besides, clustering results for the native dimer showed accessible cavities to drugs. In addition, the energetic and lipophilic analysis reveal that the higher binding energy in the native dimer can be deduced since it is more lipophilic than the mutant one, increasing non-polar interactions, which is in line with the result of MM-GBSA and SIE approaches where the van der Waals energy term has the greatest weight in the stability of the native dimer. Overall, we provide a detailed study on the Nsp9 dimer of SARS-CoV-2 that may aid in the development of new strategies for the treatment and prevention of COVID-19.

| S-EPMC8626507 | biostudies-literature

SND1 binds SARS-CoV-2 negative-sense RNA and promotes viral RNA synthesis through NSP9

Project description:Regulation of viral RNA biogenesis is fundamental to productive SARS-CoV-2 infection. To characterize host RNA-binding proteins involved in this process, we biochemically identified proteins bound to genomic and subgenomic SARS-CoV-2 RNAs. We find that the host protein SND1 specifically binds to the 5'-end of negative-sense viral RNA and is required for SARS-CoV-2 RNA synthesis. SND1-depleted cells form smaller replication organelles and display diminished virus growth kinetics. We discover that NSP9, a viral RNA-binding protein and direct SND1 interaction partner, is covalently linked to the 5'-ends of positive and negative-sense RNAs produced during infection. These linkages occur at replication-transcription initiation sites, consistent with NSP9 priming viral RNA synthesis. Mechanistically, SND1 remodels NSP9 occupancy and alters the covalent linkage of NSP9 to initiating nucleotides in viral RNA. Our findings implicate NSP9 in the initiation of SARS-CoV-2 RNA synthesis and unravel an unsuspected role of a cellular protein in orchestrating viral RNA production.

2023-10-03 | GSE217429 | GEO

Backbone chemical shift assignments for the SARS-CoV-2 non-structural protein Nsp9: intermediate (ms - ?s) dynamics in the C-terminal helix at the dimer interface.

Project description:The Betacoronavirus SARS-CoV-2 non-structural protein Nsp9 is a 113-residue protein that is essential for viral replication, and consequently, a potential target for the development of therapeutics against COVID19 infections. To capture insights into the dynamics of the protein's backbone in solution and accelerate the identification and mapping of ligand-binding surfaces through chemical shift perturbation studies, the backbone 1H, 13C, and 15N NMR chemical shifts for Nsp9 have been extensively assigned. These assignments were assisted by the preparation of an?~?70% deuterated sample and residue-specific, 15N-labelled samples (V, L, M, F, and K). A major feature of the assignments was the "missing" amide resonances for N96-L106 in the 1H-15N HSQC spectrum, a region that comprises almost the complete C-terminal ?-helix that forms a major part of the homodimer interface in the crystal structure of SARS-CoV-2 Nsp9, suggesting this region either undergoes intermediate motion in the ms to ?s timescale and/or is heterogenous. These "missing" amide resonances do not unambiguously appear in the 1H-15N HSQC spectrum of SARS-CoV-2 Nsp9 collected at a concentration of 0.0007 mM. At this concentration, at the detection limit, native mass spectrometry indicates the protein is exclusively in the monomeric state, suggesting the intermediate motion in the C-terminal of Nsp9 may be due to intramolecular dynamics. Perhaps this intermediate ms to ?s timescale dynamics is the physical basis for a previously suggested "fluidity" of the C-terminal helix that may be responsible for homophilic (Nsp9-Nsp9) and postulated heterophilic (Nsp9-Unknown) protein-protein interactions.

| S-EPMC7779335 | biostudies-literature

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