Amino acids 15–28 in the ectodomain of SARS coronavirus 3a protein induces neutralizing antibodies

Abstract

A synthetic peptide corresponding to amino acids (aa) 15-28 of the severe acute respiratory syndrome coronavirus (SARS-CoV) 3a protein was used to raise polyclonal antibodies in rabbits. This anti-3a N-terminal antibody could detect 3a protein in infected cells, as did an anti-3a C-terminal antibody previously described. The latter targeted the C-terminal cytoplasmic domain of 3a (aa 134-274). The anti-3a N-terminal antibody could detect intracellular 3a as well as 3a expressed on the cell surface. Interestingly, only the anti-3a N-terminal antibody can inhibit SARS-CoV propagation in Vero E6 culture although the binding affinity of the anti-3a N-terminal antibody was lower than the anti-3a C-terminal antibody.

Cross-reactive antibodies in convalescent SARS patients' sera against the emerging novel human coronavirus EMC (2012) by both immunofluorescent and neutralizing antibody tests

“…Of all the surface proteins, only the ectodomains of S (spike) and Orf3a can induce significant neutralizing antibody with some augmentation from the M (matrix) and E (envelope) proteins. 41,42 Though Orf3a is absent in HCoV-EMC, we cannot completely exclude the possibility that similar Orf3a-like proteins are being coded by the accessory protein gene but homology search does not reveal the presence of similar protein. All betacoronaviruses use the S protein for attachment and fusion of the virion with the host cell membrane.…”

The Role of Severe Acute Respiratory Syndrome (SARS)-Coronavirus Accessory Proteins in Virus Pathogenesis

“…The sera from rabbits immunized with recombinant ORF3a (a.a. 125–274) does not exhibit any significant neutralizing activity on SARS-CoV infected Vero E6 cells [59]. In another study, however, sera from rabbits immunized with a different recombinant ORF3a (a.a. 15–28) contains neutralizing antibodies that do inhibit SARS-CoV infection in Vero E6 cells [61]. These contrasting results could be explained by differences in the immunogenicity of the central region and C-terminal domain compared to the N-terminal ectodomain, respectively.…”

Vaccines to prevent severe acute respiratory syndrome coronavirus-induced disease

“…In addition, it was recently reported that the N-terminal domain of 3a protein elicits strong and potentially protective humoral responses in infected patients (Zhong et al, 2006). Accordingly, rabbit polyclonal antibodies raised against a synthetic peptide corresponding to aa 15-28 of 3a protein inhibit SARS-CoV propagation in Vero E6 cells, in contrast to antibodies specific for the C-terminal domain of the protein (Akerstrom et al, 2006). SARS-CoV E, M, and 7a proteins have shown low immunogenicity (Tan et al, 2004a).…”