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- Han, Dong P (x)
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Show moreThe etiological agent of severe acute respiratory syndrome (SARS) has been identified as a novel coronavirus SARS-CoV. Similar to other coronaviruses, spike (S)-glycoprotein of the virus interacts with a cellular receptor and mediates membrane fusion to allow viral entry into susceptible target cells. Accordingly, S-protein plays an important role in virus infection cycle and is the primary target of neutralizing antibodies. To begin to understand its biochemical and immunological properties, we expressed both full-length and ectodomain of the protein in various primate cells. Our results show that the protein has an electrophoretic mobility of about 160–170 kDa. The protein is glycosylated with high mannose and/or hybrid oligosaccharides, which account for approximately 30 kDa of the apparent protein mass. The detection of S-protein by immunoassays was difficult using human convalescent sera, suggesting that the protein may not elicit strong humoral immune response in virus-infected patients. We were able to pseudotype murine leukemia virus particles with S-protein and produce SARS pseudoviruses. Pseudoviruses infected Vero E6 cells in a pH-independent manner and the infection could be specifically inhibited by convalescent sera. Consistent with low levels of antibodies against S-protein, neutralizing activity was weak with 50% neutralization titers ranging between 1:15 to 1:25. To facilitate quantifying pseudovirus-infected cells, which are stained blue with X-Gal, we devised an automated procedure using an ELISPOT analyzer. The high-throughput capacity of this procedure and the safety of using SARS pseudoviruses should make possible large-scale analyses of neutralizing antibody responses against SARS-CoV.
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Show moreSevere acute respiratory syndrome (SARS) is caused by a novel coronavirus, SARS-CoV. Virus entry into cells is mediated through interactions between spike (S) glycoprotein and angiotensin-converting enzyme 2 (ACE2). Alanine scanning mutagenesis analysis was performed to identify determinants on ACE2 critical for SARS-CoV infection. Results indicated that charged amino acids between residues 22 and 57 were important, K26 and D30, in particular. Peptides representing various regions of ACE2 critical for virus infection were chemically synthesized and evaluated for antiviral activity. Two peptides (a.a. 22–44 and 22–57) exhibited a modest antiviral activity with IC(50) of about 50 μM and 6 μM, respectively. One peptide comprised of two discontinuous segments of ACE2 (a.a. 22–44 and 351–357) artificially linked together by glycine, exhibited a potent antiviral activity with IC(50) of about 0.1 μM. This novel peptide is a promising candidate as a therapeutic agent against this deadly emerging pathogen.
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