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Query: UMLS:C1175175 (SARS)
 19,188 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cell clone #21 is a long-term producer of the infectious SARS-coronavirus, although the incorporation rate of spike (S) protein into virions is significantly lower. Sequencing analysis of the viral structural proteins revealed four and one amino acid substitutions in the S and membrane (M) proteins, respectively. We demonstrated, using a viral-like particle formation system, that the S mutations were involved in the lower incorporation of the S protein into virions, although the M mutation that disrupts the glycosylation was not present in this phenotype. Further mutational experiments identified two substitutions, Y442C and L472F, within the receptor binding domain that could be critical for the reduced S incorporation, as well as reduced binding affinity between the S protein and ACE2 receptor. Thus, these two amino acid substitutions might lead to a conformational change in the S protein, resulting in reduced incorporation into viral particles.
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PMID:Reduced incorporation of SARS-CoV spike protein into viral particles due to amino acid substitutions within the receptor binding domain. 1836

Zoonotic severe acute respiratory syndrome coronavirus (SARS-CoV) likely evolved to infect humans by a series of transmission events between humans and animals in markets in China. Virus sequence data suggest that the palm civet served as an amplification host in which civet and human interaction fostered the evolution of the epidemic SARS Urbani strain. The prototypic civet strain of SARS-CoV, SZ16, was isolated from a palm civet but has not been successfully cultured in vitro. To propagate a chimeric recombinant SARS-CoV bearing an SZ16 spike (S) glycoprotein (icSZ16-S), we constructed cell lines expressing the civet ortholog (DBT-cACE2) of the SARS-CoV receptor (hACE2). Zoonotic SARS-CoV was completely dependent on ACE2 for entry. Urbani grew with similar kinetics in both the DBT-cACE2 and the DBT-hACE2 cells, while icSZ16-S only grew in DBT-cACE2 cells. The SZ16-S mutant viruses adapted to human airway epithelial cells and displayed enhanced affinity for hACE2 but exhibited severe growth defects in the DBT-cACE2 cells, suggesting that the evolutionary pathway that promoted efficient hACE2 interactions simultaneously abolished efficient cACE2 interactions. Structural modeling predicted two distinct biochemical interaction networks by which zoonotic receptor binding domain architecture can productively engage hACE2, but only the Urbani mutational repertoire promoted efficient usage of both hACE2 and cACE2 binding interfaces. Since dual species tropism was preserved in Urbani, it is likely that the virus evolved a high affinity for cACE2/hACE2 receptors through adaptation via repeated passages between human and civet hosts. Furthermore, zoonotic SARS-CoV was variably neutralized by antibodies that were effective against the epidemic strain, highlighting their utility for evaluating passive immunization efficacy.
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PMID:Pathways of cross-species transmission of synthetically reconstructed zoonotic severe acute respiratory syndrome coronavirus. 1857 4

To establish a rapid and economical method for the expression of viral proteins in high yield and purity by Pichia pastoris, the S protein of the SARS-CoV was selected in this study. Six S glycoprotein fragments were expressed in Escherichia coli BL21 and yeast KM71H strains. After purification by affinity chromatography, the protein identities were confirmed by western blot analysis, N-terminal sequencing and mass spectrometry. The proteins expressed in E. coli were low in solubility and bound by GroEL. They still formed soluble aggregates even when the GroEL was removed by urea. The proteins expressed in P. pastoris were relatively soluble. The maximal yield of the RBD reached 46 mg/l with purity greater than 95%. Pull-down assay revealed that ACE2 was specifically captured from cell lysate, indicating that the RBD was biologically active. The glycosylated and deglycosylated RBD was then subjected to SEC and results showed that deglycosylated RBD formed soluble aggregates again. Taken together, pure and biological active RBD of the S protein could be expressed in P. pastoris, and the P. pastoris expression platform will be a good alternative for the expression of viral proteins, in particular, the highly glycosylated surface proteins that mediate the tissue tropism and viral entry.
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PMID:Expression of SARS-coronavirus spike glycoprotein in Pichia pastoris. 1895 13

The receptor-binding domain (RBD) on spike protein of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) is the main region interacting with the viral receptor-ACE2 and is a useful target for induction of neutralizing antibodies against SARS-CoV infection. Here we generated two monoclonal antibodies (mAbs), targeting RBD, with marked virus neutralizing activity. The mAbs recognize a new conformational epitope which consists of several discontinuous peptides (aa. 343-367, 373-390 and 411-428) and is spatially located neighboring the receptor-binding motif (RPM) region of the RBD. Importantly, W423 and N424 residues are essential for mAb recognition and are highly conserved among 107 different strains of SARS, indicating that the residues are the most critical in the epitope which is a novel potential target for therapeutic mAbs. A human-mouse chimeric antibody, based upon the original murine mAb, was also constructed and shown to possess good neutralizing activity and high affinity.
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PMID:Conserved amino acids W423 and N424 in receptor-binding domain of SARS-CoV are potential targets for therapeutic monoclonal antibody. 1898 62

Severe acute respiratory syndrome (SARS) coronavirus (CoV) contains a spike (S) protein that binds to a receptor molecule (angiotensin-converting enzyme 2; ACE2), induces membrane fusion, and serves as a neutralizing epitope. To study the functions of the S protein, we describe here the generation of SARS-CoV S protein-bearing vesicular stomatitis virus (VSV) pseudotype using a VSVdeltaG*/GFP system in which the G gene is replaced by the green fluorescent protein (GFP) gene (VSV-SARS-CoV-St19/GFP). Partial deletion of the cytoplasmic domain of SARS-CoV S protein (SARS-CoV-St19) allowed efficient incorporation into the VSV particle that enabled the generation of a high titer of pseudotype virus. Neutralization assay with anti-SARS-CoV antibody revealed that VSV-SARS-St19/GFP pseudotype infection is mediated by SARS-CoV S protein. The VSVdeltaaG*/SEAP system, which secretes alkaline phosphatase instead of GFP, was also generated as a VSV pseudotype having SARS-CoV S protein (VSV-SARS-CoV-St19/SEAP). This system enabled high-throughput analysis of SARS-CoV S protein-mediated cell entry by measuring alkaline phosphatase activity. Thus, VSV pseudotyped with SARS-CoV S protein is useful for developing a rapid detection system for neutralizing antibody specific for SARS-CoV infection as well as studying the S-mediated cell entry of SARS-CoV.
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PMID:Pseudotyped vesicular stomatitis virus for analysis of virus entry mediated by SARS coronavirus spike proteins. 1905 67

In this study, infection of 293/ACE2 cells with severe acute respiratory syndrome coronavirus (SARS-CoV) activated several apoptosis-associated events, namely, cleavage of caspase-3, caspase-8, and poly(ADP-ribose) polymerase 1 (PARP), and chromatin condensation and the phosphorylation and hence inactivation of the eukaryotic translation initiation factor 2alpha (eIF2alpha). In addition, two of the three cellular eIF2alpha kinases known to be virus induced, protein kinase R (PKR) and PKR-like endoplasmic reticulum kinase (PERK), were activated by SARS-CoV. The third kinase, general control nonderepressible-2 kinase (GCN2), was not activated, but late in infection the level of GCN2 protein was significantly reduced. Reverse transcription-PCR analyses revealed that the reduction of GCN2 protein was not due to decreased transcription or stability of GCN2 mRNA. The specific reduction of PKR protein expression by antisense peptide-conjugated phosphorodiamidate morpholino oligomers strongly reduced cleavage of PARP in infected cells. Surprisingly, the knockdown of PKR neither enhanced SARS-CoV replication nor abrogated SARS-CoV-induced eIF2alpha phosphorylation. Pretreatment of cells with beta interferon prior to SARS-CoV infection led to a significant decrease in PERK activation, eIF2alpha phosphorylation, and SARS-CoV replication. The various effects of beta interferon treatment were found to function independently on the expression of PKR. Our results show that SARS-CoV infection activates PKR and PERK, leading to sustained eIF2alpha phosphorylation. However, virus replication was not impaired by these events, suggesting that SARS-CoV possesses a mechanism to overcome the inhibitory effects of phosphorylated eIF2alpha on viral mRNA translation. Furthermore, our data suggest that viral activation of PKR can lead to apoptosis via a pathway that is independent of eIF2alpha phosphorylation.
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PMID:Severe acute respiratory syndrome coronavirus triggers apoptosis via protein kinase R but is resistant to its antiviral activity. 1910 97

Angiotensin-converting enzyme (ACE)-2 is a homolog of the well-characterized plasma membrane-bound angiotensin-converting enzyme. ACE2 is thought to play a critical role in regulating heart function, and in 2003, ACE2 was identified as a functional receptor for severe acute respiratory syndrome coronavirus. We have recently shown that like ACE, ACE2 undergoes ectodomain shedding and that this shedding event is up-regulated by phorbol esters. In the present study, we used gel shift assays to demonstrate that calmodulin, an intracellular calcium-binding protein implicated in the regulation of other ectodomain shedding events, binds a 16-amino acid synthetic peptide corresponding to residues 762-777 within the cytoplasmic domain of human ACE2, forming a calcium-dependent calmodulin-peptide complex. Furthermore, we have demonstrated that ACE2 expressed in Chinese hamster ovary cells specifically binds to glutathione-S-transferase-calmodulin, but not glutathione-S-transferase alone, in pull-down assays using cell lysates. Finally, to investigate whether calmodulin has any effect on ACE2 ectodomain shedding in cells that endogenously express the enzyme, cells from a human liver cell line (Huh-7) expressing ACE2 were incubated with calmodulin-specific inhibitors, trifluoperazine and calmidazolium. Both trifluoperazine (25 micromol/liter) and calmidazolium, (25 micromol/liter) significantly increased the release of ACE2 into the medium (44.1 +/- 10.8%, P < 0.05, Student's t test; unpaired, two-tailed, and 51.1 +/- 7.4% P < 0.05, one-way ANOVA, respectively;), as analyzed by an ACE2-specific quenched fluorescence substrate assay. We also show that the calmodulin-specific inhibitor-stimulated shedding of ACE2 is independent from phorbol ester-induced shedding. In summary, we have demonstrated that calmodulin is able to bind ACE2 and suggest that the ACE2 ectodomain shedding and/or sheddase(s) activation regulated by calmodulin is independent from the phorbol ester-induced shedding.
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PMID:The identification of a calmodulin-binding domain within the cytoplasmic tail of angiotensin-converting enzyme-2. 1916 71

Several respiratory viruses, including influenza virus and severe acute respiratory syndrome coronavirus (SARS-CoV), produce more severe disease in the elderly, yet the molecular mechanisms governing age-related susceptibility remain poorly studied. Advanced age was significantly associated with increased SARS-related deaths, primarily due to the onset of early- and late-stage acute respiratory distress syndrome (ARDS) and pulmonary fibrosis. Infection of aged, but not young, mice with recombinant viruses bearing spike glycoproteins derived from early human or palm civet isolates resulted in death accompanied by pathological changes associated with ARDS. In aged mice, a greater number of differentially expressed genes were observed than in young mice, whose responses were significantly delayed. Differences between lethal and nonlethal virus phenotypes in aged mice could be attributed to differences in host response kinetics rather than virus kinetics. SARS-CoV infection induced a range of interferon, cytokine, and pulmonary wound-healing genes, as well as several genes associated with the onset of ARDS. Mice that died also showed unique transcriptional profiles of immune response, apoptosis, cell cycle control, and stress. Cytokines associated with ARDS were significantly upregulated in animals experiencing lung pathology and lethal disease, while the same animals experienced downregulation of the ACE2 receptor. These data suggest that the magnitude and kinetics of a disproportionately strong host innate immune response contributed to severe respiratory stress and lethality. Although the molecular mechanisms governing ARDS pathophysiology remain unknown in aged animals, these studies reveal a strategy for dissecting the genetic pathways by which SARS-CoV infection induces changes in the host response, leading to death.
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PMID:Early upregulation of acute respiratory distress syndrome-associated cytokines promotes lethal disease in an aged-mouse model of severe acute respiratory syndrome coronavirus infection. 1942 84

Infection by severe acute respiratory syndrome coronavirus (SARS-CoV) is initiated by specific interactions between the SARS-CoV spike (S) protein and its receptor ACE2. In this report, we screened a peptide library representing the SARS-CoV S protein sequence using a human immunodeficiency virus-based pseudotyping system to identify specific regions that affect viral entry. One of the 169 peptides screened, peptide 9626 (S residues 217-234), inhibited SARS-CoV S-mediated entry of the pseudotyped virions in 293T cells expressing a functional SARS-CoV receptor (human angiotensin-converting enzyme 2) in a dose-dependent manner (IC(50) approximately 11 microM). Alanine scanning mutagenesis was performed to assess the roles of individual residues within this region of S, which was previously uncharacterized. The effects included significant reductions in expression (K223A), viral incorporation (L218A, I230A, and N232A), and reduced viral entry (L224A, L226A, I228A, T231A, and F233A). Taken together, these results reveal a new region of the S protein that is crucial for SARS-CoV entry.
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PMID:Identification of a new region of SARS-CoV S protein critical for viral entry. 1985 13

Severe acute respiratory syndrome (SARS), caused by the coronavirus SARS-CoV, is an acute infectious disease with significant mortality. A typical clinical feature associated with SARS is pulmonary fibrosis and associated lung failure. In the aftermath of the SARS epidemic, although significant progress towards understanding the underlying molecular mechanism of the infection has been made, a large gap still remains in our knowledge regarding how SARS-CoV interacts with the host cell at the onset of infection. The rapidly changing viral genome adds another variable to this equation. We have focused on a novel concept of microRNA (miRNA)-mediated host-virus interactions in bronchoalveolar stem cells (BASCs) at the onset of infection by correlating the "BASC-microRNome" with their targets within BASCs and viral genome. This work encompasses miRNA array data analysis, target prediction, and miRNA-mRNA enrichment analysis and develops a complex interaction map among disease-related factors, miRNAs, and BASCs in SARS pathway, which will provide some clues for diagnostic markers to view an overall interplay leading to disease progression. Our observation reveals the BASCs (Sca-1+ CD34+ CD45- Pecam-), a subset of Oct-4+ ACE2+ epithelial colony cells at the broncho-alveolar duct junction, to be the prime target cells of SARS-CoV infection. Upregulated BASC miRNAs-17*, -574-5p, and -214 are co-opted by SARS-CoV to suppress its own replication and evade immune elimination until successful transmission takes place. Viral Nucleocapsid and Spike protein targets seem to co-opt downregulated miR-223 and miR-98 respectively within BASCs to control the various stages of BASC differentiation, activation of inflammatory chemokines, and downregulation of ACE2. All these effectively accounts for a successful viral transmission and replication within BASCs causing continued deterioration of lung tissues and apparent loss of capacity for lung repair. Overall, this investigation reveals another mode of exploitation of cellular miRNA machinery by virus to their own advantage.
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PMID:MicroRNome analysis unravels the molecular basis of SARS infection in bronchoalveolar stem cells. 1991 17


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