scholarly journals Structural basis for translational shutdown and immune evasion by the Nsp1 protein of SARS-CoV-2

Science ◽  
2020 ◽  
Vol 369 (6508) ◽  
pp. 1249-1255 ◽  
Author(s):  
Matthias Thoms ◽  
Robert Buschauer ◽  
Michael Ameismeier ◽  
Lennart Koepke ◽  
Timo Denk ◽  
...  
Keyword(s):  
Messenger Rna ◽  
Nonstructural Protein ◽  
Ribosomal Subunit ◽  
Mrna Translation ◽  
Structural Basis ◽  
Innate Immune Responses ◽  
Structure Based Drug Design ◽  
Nonstructural Protein 1 ◽  
C Terminus

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the current coronavirus disease 2019 (COVID-19) pandemic. A major virulence factor of SARS-CoVs is the nonstructural protein 1 (Nsp1), which suppresses host gene expression by ribosome association. Here, we show that Nsp1 from SARS-CoV-2 binds to the 40S ribosomal subunit, resulting in shutdown of messenger RNA (mRNA) translation both in vitro and in cells. Structural analysis by cryo–electron microscopy of in vitro–reconstituted Nsp1-40S and various native Nsp1-40S and -80S complexes revealed that the Nsp1 C terminus binds to and obstructs the mRNA entry tunnel. Thereby, Nsp1 effectively blocks retinoic acid–inducible gene I–dependent innate immune responses that would otherwise facilitate clearance of the infection. Thus, the structural characterization of the inhibitory mechanism of Nsp1 may aid structure-based drug design against SARS-CoV-2.

scholarly journals Structural basis for translational shutdown and immune evasion by the Nsp1 protein of SARS-CoV-2

2020 ◽  
Author(s):  
Matthias Thoms ◽  
Robert Buschauer ◽  
Michael Ameismeier ◽  
Lennart Koepke ◽  
Timo Denk ◽  
...  
Keyword(s):  
Nonstructural Protein ◽  
Mrna Translation ◽  
Structural Basis ◽  
Innate Immune Responses ◽  
Structure Based Drug Design ◽  
Nonstructural Protein 1 ◽  
Cryo Electron Microscopy ◽  
C Terminus

AbstractSARS-CoV-2 is the causative agent of the current COVID-19 pandemic. A major virulence factor of SARS-CoVs is the nonstructural protein 1 (Nsp1) which suppresses host gene expression by ribosome association via an unknown mechanism. Here, we show that Nsp1 from SARS-CoV-2 binds to 40S and 80S ribosomes, resulting in shutdown of capped mRNA translation both in vitro and in cells. Structural analysis by cryo-electron microscopy (cryo-EM) of in vitro reconstituted Nsp1-40S and of native human Nsp1-ribosome complexes revealed that the Nsp1 C-terminus binds to and obstructs the mRNA entry tunnel. Thereby, Nsp1 effectively blocks RIG-I-dependent innate immune responses that would otherwise facilitate clearance of the infection. Thus, the structural characterization of the inhibitory mechanism of Nsp1 may aid structure-based drug design against SARS-CoV-2.

scholarly journals Structural characterization of Nonstructural protein 1 from SARS-CoV-2

2020 ◽  
Author(s):  
Cameron Semper ◽  
Nobuhiko Watanabe ◽  
Alexei Savchenko
Keyword(s):  
Crystal Structure ◽  
Rna Virus ◽  
Nonstructural Protein ◽  
Ribosomal Subunit ◽  
Structural Features ◽  
Globular Domain ◽  
Nonstructural Protein 1 ◽  
C Terminus ◽  
40S Ribosomal Subunit ◽  
Efficient Replication

AbstractSevere acute respiratory syndrome (SARS) coronavirus-2 (SARS-CoV-2) is a single-stranded, enveloped RNA virus and the etiological agent of the current COVID-19 pandemic. Efficient replication of the virus relies on the activity of nonstructural protein 1 (Nsp1), a major virulence factor shown to facilitate suppression of host gene expression through promotion of host mRNA degradation and interaction with the 40S ribosomal subunit. Here, we report the crystal structure of the globular domain of SARS-CoV-2 Nsp1, encompassing residues 13 to 127, at a resolution of 1.65 Å. Our structure features a six-stranded, capped β-barrel motif similar to Nsp1from SARS-CoV and reveals how variations in amino acid sequence manifest as distinct structural features. Through comparative analysis of structural homologues, we identified a topological signature associated with this protein fold that facilitated modeling of Nsp1 from MERS-CoV. Combining our high-resolution crystal structure with existing data on the C-terminus of Nsp1 from SARS-CoV-2, we propose a model of the full-length protein. Our results provide unparalleled insight into the molecular structure of a major pathogenic determinant of SARS-CoV-2.

scholarly journals The N-terminal and central domains of CoV-2 nsp1 play key functional roles in suppression of cellular gene expression and preservation of viral gene expression

2021 ◽  
Author(s):  
Aaron Stephen Mendez ◽  
Michael Ly ◽  
Angélica M. González-Sánchez ◽  
Ella Hartenian ◽  
Nicholas Ingolia ◽  
...  
Keyword(s):  
Gene Expression ◽  
Mutational Analysis ◽  
Nonstructural Protein ◽  
Ribosomal Subunit ◽  
Viral Gene ◽  
Viral Mrna ◽  
Cellular Gene ◽  
Cellular Gene Expression ◽  
Nonstructural Protein 1

Nonstructural protein 1 (nsp1) is the first viral protein synthesized during coronavirus (CoV) infection and is a key virulence factor that dampens the innate immune response. It restricts cellular gene expression through a combination of inhibiting translation by blocking the mRNA entry channel of the 40S ribosomal subunit and by promoting mRNA degradation. We performed a detailed structure-guided mutational analysis of CoV-2 nsp1 coupled with in vitro and cell-based functional assays, revealing insight into how it coordinates these activities against host but not viral mRNA. We found that residues in the N-terminal and central regions of nsp1 not involved in docking into the 40S mRNA entry channel nonetheless stabilize its association with the ribosome and mRNA, thereby enhancing its restriction of host gene expression. These residues are also critical for the ability of mRNA containing the CoV-2 leader sequence to escape translational repression. Notably, we identify CoV-2 nsp1 mutants that gain the ability to repress translation of viral leader-containing transcripts. These data support a model in which viral mRNA binding functionally alters the association of nsp1 with the ribosome, which has implications for drug targeting and understanding how engineered or emerging mutations in CoV-2 nsp1 could attenuate the virus.

scholarly journals SARS-CoV-2 Nsp1 suppresses host but not viral translation through a bipartite mechanism

2020 ◽  
Author(s):  
Ming Shi ◽  
Longfei Wang ◽  
Pietro Fontana ◽  
Setu Vora ◽  
Ying Zhang ◽  
...  
Keyword(s):  
Nonstructural Protein ◽  
Ribosomal Subunit ◽  
Direct Interaction ◽  
Mrna Translation ◽  
Protein Translation ◽  
Host Protein ◽  
Terminal Domain ◽  
Nonstructural Protein 1 ◽  
40S Ribosomal Subunit ◽  
Open Question

SUMMARYThe Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a highly contagious virus that underlies the current COVID-19 pandemic. SARS-CoV-2 is thought to disable various features of host immunity and cellular defense. The SARS-CoV-2 nonstructural protein 1 (Nsp1) is known to inhibit host protein translation and could be a target for antiviral therapy against COVID-19. However, how SARS-CoV-2 circumvents this translational blockage for the production of its own proteins is an open question. Here, we report a bipartite mechanism of SARS-CoV-2 Nsp1 which operates by: (1) hijacking the host ribosome via direct interaction of its C-terminal domain (CT) with the 40S ribosomal subunit and (2) specifically lifting this inhibition for SARS-CoV-2 via a direct interaction of its N-terminal domain (NT) with the 5’ untranslated region (5’ UTR) of SARS-CoV-2 mRNA. We show that while Nsp1-CT is sufficient for binding to 40S and inhibition of host protein translation, the 5’ UTR of SARS-CoV-2 mRNA removes this inhibition by binding to Nsp1-NT, suggesting that the Nsp1-NT-UTR interaction is incompatible with the Nsp1-CT-40S interaction. Indeed, lengthening the linker between Nsp1-NT and Nsp1-CT of Nsp1 progressively reduced the ability of SARS-CoV-2 5’ UTR to escape the translational inhibition, supporting that the incompatibility is likely steric in nature. The short SL1 region of the 5’ UTR is required for viral mRNA translation in the presence of Nsp1. Thus, our data provide a comprehensive view on how Nsp1 switches infected cells from host mRNA translation to SARS-CoV-2 mRNA translation, and that Nsp1 and 5’ UTR may be targeted for anti-COVID-19 therapeutics.

scholarly journals Structural Basis and Function of the N Terminus of SARS-CoV-2 Nonstructural Protein 1

2021 ◽  
Author(s):  
Kaitao Zhao ◽  
Zunhui Ke ◽  
Hongbing Hu ◽  
Yahui Liu ◽  
Aixin Li ◽  
...  
Keyword(s):  
Severe Acute Respiratory Syndrome ◽  
Nonstructural Protein ◽  
Protein Translation ◽  
Host Protein ◽  
Structural Basis ◽  
Pathogenic Factor ◽  
Nonstructural Protein 1 ◽  
C Terminus ◽  
N Terminus ◽  
And Function

Nonstructural protein 1 (Nsp1) of severe acute respiratory syndrome coronaviruses (SARS-CoVs) is an important pathogenic factor that inhibits host protein translation by means of its C terminus. However, its N-terminal function remains elusive.

scholarly journals Structural basis for the transition from translation initiation to elongation by an 80S-eIF5B complex

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Jinfan Wang ◽  
Jing Wang ◽  
Byung-Sik Shin ◽  
Joo-Ran Kim ◽  
Thomas E. Dever ◽  
...  
Keyword(s):  
Single Molecule ◽  
Translation Initiation ◽  
Messenger Rna ◽  
Ribosomal Subunit ◽  
Mrna Translation ◽  
Start Codon ◽  
Structural Basis ◽  
Large Ribosomal Subunit ◽  
Reading Frame ◽  
Fluorescence Measurements

Abstract Recognition of a start codon by the initiator aminoacyl-tRNA determines the reading frame of messenger RNA (mRNA) translation by the ribosome. In eukaryotes, the GTPase eIF5B collaborates in the correct positioning of the initiator Met-tRNAiMet on the ribosome in the later stages of translation initiation, gating entrance into elongation. Leveraging the long residence time of eIF5B on the ribosome recently identified by single-molecule fluorescence measurements, we determine the cryoEM structure of the naturally long-lived ribosome complex with eIF5B and Met-tRNAiMet immediately before transition into elongation. The structure uncovers an unexpected, eukaryotic specific and dynamic fidelity checkpoint implemented by eIF5B in concert with components of the large ribosomal subunit.

scholarly journals Structural basis of GTPase-mediated mitochondrial ribosome biogenesis and recycling

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Hauke S. Hillen ◽  
Elena Lavdovskaia ◽  
Franziska Nadler ◽  
Elisa Hanitsch ◽  
Andreas Linden ◽  
...  
Keyword(s):  
Ribosomal Proteins ◽  
Ribosome Biogenesis ◽  
Ribosomal Subunit ◽  
Structural Basis ◽  
Peptidyl Transferase ◽  
Mitochondrial Ribosomes ◽  
Mitochondrial Ribosome ◽  
In Vitro Reconstitution

AbstractRibosome biogenesis requires auxiliary factors to promote folding and assembly of ribosomal proteins and RNA. Particularly, maturation of the peptidyl transferase center (PTC) is mediated by conserved GTPases, but the molecular basis is poorly understood. Here, we define the mechanism of GTPase-driven maturation of the human mitochondrial large ribosomal subunit (mtLSU) using endogenous complex purification, in vitro reconstitution and cryo-EM. Structures of transient native mtLSU assembly intermediates that accumulate in GTPBP6-deficient cells reveal how the biogenesis factors GTPBP5, MTERF4 and NSUN4 facilitate PTC folding. Addition of recombinant GTPBP6 reconstitutes late mtLSU biogenesis in vitro and shows that GTPBP6 triggers a molecular switch and progression to a near-mature PTC state. Additionally, cryo-EM analysis of GTPBP6-treated mature mitochondrial ribosomes reveals the structural basis for the dual-role of GTPBP6 in ribosome biogenesis and recycling. Together, these results provide a framework for understanding step-wise PTC folding as a critical conserved quality control checkpoint.

Influenza A viruses balance ER stress with host protein synthesis shutoff

2021 ◽  
Vol 118 (36) ◽  
pp. e2024681118
Author(s):  
Beryl Mazel-Sanchez ◽  
Justyna Iwaszkiewicz ◽  
Joao P. P. Bonifacio ◽  
Filo Silva ◽  
Chengyue Niu ◽  
...  
Keyword(s):  
Viral Replication ◽  
Er Stress ◽  
Host Cell ◽  
Messenger Rna ◽  
Influenza A ◽  
Nonstructural Protein ◽  
Host Protein ◽  
Stress Induction ◽  
Nonstructural Protein 1

Excessive production of viral glycoproteins during infections poses a tremendous stress potential on the endoplasmic reticulum (ER) protein folding machinery of the host cell. The host cell balances this by providing more ER resident chaperones and reducing translation. For viruses, this unfolded protein response (UPR) offers the potential to fold more glycoproteins. We postulated that viruses could have developed means to limit the inevitable ER stress to a beneficial level for viral replication. Using a relevant human pathogen, influenza A virus (IAV), we first established the determinant for ER stress and UPR induction during infection. In contrast to a panel of previous reports, we identified neuraminidase to be the determinant for ER stress induction, and not hemagglutinin. IAV relieves ER stress by expression of its nonstructural protein 1 (NS1). NS1 interferes with the host messenger RNA processing factor CPSF30 and suppresses ER stress response factors, such as XBP1. In vivo viral replication is increased when NS1 antagonizes ER stress induction. Our results reveal how IAV optimizes glycoprotein expression by balancing folding capacity.

scholarly journals Evolutionary and structural analysis of SARS-CoV-2 specific evasion of host immunity

2020 ◽  
Vol 21 (6-8) ◽  
pp. 409-419
Author(s):  
Irfan Hussain ◽  
Nashaiman Pervaiz ◽  
Abbas Khan ◽  
Shoaib Saleem ◽  
Huma Shireen ◽  
...  
Keyword(s):  
Immune Responses ◽  
Nonstructural Protein ◽  
Critical Role ◽  
Clinical Manifestations ◽  
Host Immunity ◽  
Innate Immune ◽  
Host Immune System ◽  
Innate Immune Responses ◽  
In Vivo Models

AbstractThe outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is spreading fast worldwide. There is a pressing need to understand how the virus counteracts host innate immune responses. Deleterious clinical manifestations of coronaviruses have been associated with virus-induced direct dysregulation of innate immune responses occurring via viral macrodomains located within nonstructural protein-3 (Nsp3). However, no substantial information is available concerning the relationship of macrodomains to the unusually high pathogenicity of SARS-CoV-2. Here, we show that structural evolution of macrodomains may impart a critical role to the unique pathogenicity of SARS-CoV-2. Using sequence, structural, and phylogenetic analysis, we identify a specific set of historical substitutions that recapitulate the evolution of the macrodomains that counteract host immune response. These evolutionary substitutions may alter and reposition the secondary structural elements to create new intra-protein contacts and, thereby, may enhance the ability of SARS-CoV-2 to inhibit host immunity. Further, we find that the unusual virulence of this virus is potentially the consequence of Darwinian selection‐driven epistasis in protein evolution. Our findings warrant further characterization of macrodomain-specific evolutionary substitutions in in vitro and in vivo models to determine their inhibitory effects on the host immune system.

scholarly journals CONTROLLED PROTEOLYSIS OF NASCENT POLYPEPTIDES IN RAT LIVER CELL FRACTIONS

1970 ◽  
Vol 45 (1) ◽  
pp. 130-145 ◽  
Author(s):  
G. Blobel ◽  
D. D. Sabatini
Keyword(s):  
Messenger Rna ◽  
Ribosomal Proteins ◽  
Ribosomal Subunit ◽  
Subunit Structure ◽  
Amino Acid Residues ◽  
Nascent Polypeptide ◽  
Nascent Chain ◽  
Cell Fractions ◽  
Carboxy Terminal

Free ribosomes containing nascent polypeptide chains labeled in vitro were submitted to proteolysis at 0° by a mixture of trypsin and chymotrypsin. Sucrose gradient analysis showed that polysome patterns are retained even after 24 hr of proteolysis in the cold, while messenger RNA-free ribosomes (generated progressively during in vitro incorporation) are, within 2 hr, completely dissociated into subunits by trypsin. Although ribosomes and subunits are not extensively degraded into smaller fragments during low temperature proteolysis, changes in the acrylamide gel electrophoresis pattern showed that most ribosomal proteins are accessible to and are partially degraded by the proteases. Ribosome-bound nascent polypeptides are partially resistant to proteolysis at 0°, although they are totally digested at 37° or when the ribosomal subunit structure is disrupted by other means. Radioactivity incorporated into nascent chains during incubation times shorter than 3 min was mostly resistant to digestion at 0°. A larger fraction of the initial radioactivity became degraded in ribosomes which incorporated for longer times. In these ribosomes, the amount of radioactivity which was resistant to proteolysis was constant and independent of the initial value, which reflects the labeled length of the nascent chains. These results suggest that the growing end of the nascent polypeptide is resistant to digestion and is protected from proteolytic attack by the ribosomal structure. A pulse and chase experiment confirmed this suggestion, showing that the protected segment is located at the carboxy-terminal end of the nascent chain. The protected segment was contained in the large ribosomal subunit and had a length of ∼39 amino acid residues, as estimated by chromatography on Sephadex G-50.

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