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Earlier electron microscopy studies of the location of various antigenic sites in tobacco mosaic virus indicated that epitopes specific for the quaternary structure and absent in dissociated viral subunits (so-called neotopes) were present along the entire length of the virus particle. In contrast, epitopes expressed in both intact particles and dissociated subunits (so-called metatopes) were found only at the one extremity of the particle containing the 5' end of the RNA. In the present study, the binding properties of antibodies to neotopes and metatopes were studied with the BIAcore. From the results of capture assays with viral subunits and on the basis of binding stoichiometry calculations, it was possible to demonstrate the presence of neotope and metatope specificities on additional parts of the viral surface where they had not been identified before by classical immunoassays. In two site binding assays it was also found that a neotope specificity could be induced in dissociated viral subunits by the binding of a first antimetatope antibody. The results clearly demonstrated the superiority of the biosensor technology for mapping conformational epitopes in viral proteins.