Antigenic and structural variation in the major nucleocapsid protein of respiratory syncytial virus

Antigenic and structural variation in the major nucleocapsid protein, VPN41, from different strains of respiratory syncytial (RS) virus was observed using a combination of monoclonal antibodies and two-dimensional peptide mapping. Limited trypsin treatment of intact nucleocapsids produced two peptide fragments Mr 27K and Mr 14K. Two monoclonal antibodies, N1 and N2, reactive with primary sequence epitopes located on intact nucleocapsids also reacted with either the 27K fragment (N2) or the 14K fragment (N1). Competitive radioimmunoassay studies using N1 and N2 antibodies revealed two discrete antigenic groups among the seven human strains of RS virus examined. A bovine strain of RS virus, although antigenically similar to the human strain of RS virus, was placed in a separate group. Two-dimensional peptide mapping of 125I-labelled VPN41 purified by SDS-PAGE revealed extensive structural homology between all strains. However, several unique tryptic/chymotryptic peptides supported the grouping obtained with the monoclonal antibodies.