Antigenicity of the norovirus capsid

The purpose of this study was to produce monoclonal antibodies against prevalent genogroup I (GI) and genogroup II (GII) noroviruses. Monoclonal antibody CM45 was raised to the Leeds capsid protein (GIId) and cross-reacted with GIIb, GIIc and GIId noroviruses. Monoclonal antibody CM55 was raised to the Toronto virus capsid protein (GIIa) and was specific for GIIa noroviruses. These monoclonal antibodies were incorporated into Enzyme Linked Immunosorbent Assays (ELISAs) for the detection of GII noroviruses in clinical specimens and in the future will be used in epidemiological studies. Monoclonal antibody CM54 was raised to the Southampton virus (SV) capsid protein (GIa) and cross-reacted with GI capsid proteins. To characterise the monoclonal antibody binding site a series of truncated forms of the SV capsid protein were expressed as fusions to GST in E. coli. Immunoblot analysis indicated the monoclonal antibody binding site was located between amino acid residues 102-255 of the SV capsid protein. The epitope recognised by monoclonal antibody CM54 was mapped using a peptide array. Monoclonal antibody CM54 bound to the sequence LEDVRN. Alignment of norovirus capsid protein sequences illustrated the epitope (LEDVRN) was common to GI capsid proteins, but not present in GII capsid proteins. Interestingly this epitope was also present in GIIIb capsid protein sequences. Monoclonal antibody CM54 reacted by ELISA and immunoblot to NA-2 (GIIIb) VLPs. The epitope recognised by monoclonal antibody CM39 was also deduced. Monoclonal antibody CM39 reacts to Jena virus (JV), a bovine norovirus (GIIIa). Monoclonal antibody CM39 bound to the pentapeptide sequence PTAGA, which is common to the genogroup III (GIII) noroviruses. Interestingly, both of these epitopes are present in the shell domain of the capsid protein. This work described the precise molecular recognition sequence of two monoclonal antibodies and the binding sites were mapped on the published three dimensional structure of the norovirus capsid protein.