Severe acute respiratory syndrome coronavirus (SARS-CoV) encodes a highly basic nucleocapsid (N) protein which can inhibit the synthesis of type I interferon (IFN), but the molecular mechanism of this antagonism remains to be identified. In this study, we demonstrated that the N protein of SARS-CoV could inhibit IFN-beta (IFN-β) induced by poly(I:C) or Sendai virus. However, we found that N protein could not inhibit IFN-β production induced by overexpression of downstream signaling molecules of two important IFN-β induction pathways, toll-like receptor 3 (TLR3)- and RIG-I-like receptors (RLR)-dependent pathways. These results indicate that SARS-CoV N protein targets the initial step, probably the cellular PRRs (pattern recognition receptors)-RNAs-recognition step in the innate immune pathways, to suppress IFN expression responses. In addition, co-immunoprecipitation assays revealed that N protein did not interact with RIG-I or MDA5. Further, an assay using truncated mutants revealed that the C-terminal domain of N protein was critical for its antagonism of IFN induction, and the N deletion mutant impaired for RNA-binding almost completely lost the IFN-β antagonist activity. These results contribute to our further understanding of the pathogenesis of SARS-CoV.

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Eukaryotic cellular mRNAs and many viral mRNAs contain a modified 5=-terminal "cap" structure that is essential for efficient splicing, nuclear export, translation, and stability of the mRNAs (1, 2). The cap structures are usually formed by three sequential enzymatic reactions: (i) the 5=-triphosphate end of the nascent mRNA is hydrolyzed to a diphosphate by RNA triphosphatase (TPase); (ii) a GMP residue derived from GTP is transferred to the diphosphate mRNA by RNA guanylyltransferase (GTase) via a two-step reaction; and (iii) the guanosine cap is methylated by guanine-N7-methyltransferase (N7-MTase) at the N7 position to generate a cap-0 structure (m 7 GpppN) in the presence of the methyl group donor S-adenosyl-

Coronaviruses are the etiological agents of respiratory and enteric diseases in humans and livestock, exemplified by the life-threatening severe acute respiratory syndrome (SARS) caused by SARS coronavirus (SARS-CoV). However, effective means for combating coronaviruses are still lacking. The interaction between nonstructural protein (nsp) 10 and nsp16 has been demonstrated and the crystal structure of SARS-CoV nsp16/10 complex has been revealed. As nsp10 acts as an essential trigger to activate the 2'-O-methyltransferase activity of nsp16, short peptides derived from nsp10 may have inhibitory effect on viral 2'-O-methyltransferase activity. In this study, we revealed that the domain of aa 65-107 of nsp10 was sufficient for its interaction with nsp16 and the region of aa 42-120 in nsp10, which is larger than the interaction domain, was needed for stimulating the nsp16 2'-O-methyltransferase activity. We further showed that two short peptides derived from the interaction domain of nsp10 could inhibit the 2'-O-methyltransferase activity of SARS-CoV nsp16/10 complex, thus providing a novel strategy and proof-of-principle study for developing peptide inhibitors against SARS-CoV.

Sepsis‐induced myocardial dysfunction (SIMD) causes high mortality in seriously ill patients. Ginsenoside Rg1 has been proven to have effective anti‐inflammatory and antiapoptotic properties. However, the specific role of Rg1 in SIMD and the molecular mechanism remain unclear. Hence, we aimed to investigate the latent effects of ginsenoside Rg1 against SIMD and explore its underlying mechanisms. Male C57BL/6J mice and neonatal rat cardiomyocytes (NRCMs) were used as in vivo and in vitro models, respectively. Western blot analysis was used to detect the level of protein expression, and reverse transcription polymerase chain reaction was conducted to determine the messenger RNA expression of inflammatory factors. The terminal deoxynucleotidyl transferase‐mediated nick end labeling assay and flow cytometry were used to determine the apoptosis rate. Echocardiography was performed to assess cardiac function. The results showed that Rg1 improved cardiac function and attenuated lipopolysaccharide (LPS)‐induced apoptosis and inflammation in mice. In addition, in NRCMs, Rg1 downregulated the expression of LPS‐induced inflammatory cytokines and reversed the increased expression of Toll‐like receptor 4 (TLR4), nuclear factor‐κB (NF‐κB), and NOD‐like receptor 3 (NLRP3). In addition, treatment with TLR4 small interfering RNA (siRNA), a p‐NF‐κB inhibitor, or NLRP3 siRNA suppressed LPS‐induced apoptosis and inflammation. In conclusion, Rg1 can attenuate LPS‐induced inflammation and apoptosis both in NRCMs and septic mice and restore impaired cardiac function. Moreover, Rg1 may exert its effect via blocking the TLR4/NF‐κB/NLRP3 pathway.