SUBUNIT INTERACTION IN B19 PARVOVIRUS EMPTY CAPSIDS

B19 parvovirus is a small single-stranded DNA virus with a genome that encodes only two structural proteins, designated VP1 and VP2. 60 copi es of the structural proteins assemble into the viral capsid, with app roximately 95% VP2 and 5% VP1. Recombinant empty capsids composed of V P2 alone or of VP2 and VP1 self-assemble into particles that are morph ologically indistinguishable from full virions. Empty capsids containi ng both VP2 and VP1 elicit a strong neutralizing antibody response whe n used to immunize rabbits. Capsids containing only VP2 are similarly antigenic but elicit only weak neutralizing activity. We performed fin e structure epitope mapping by measuring the reactivity of antisera ra ised against capsids composed of VP2 and VP1 or VP2 alone against 85 o verlapping peptides spanning the sequence of the two structural protei ns. A profile of the antigenic difference between empty capsids with a nd without VP1 was produced from the resulting data. This profile divi ded the sequence of the structural proteins into four regions that cor related well with expected viral structures. Thus, the addition of a s mall number of VP1 residues altered the antigenicity of the entire cap sid. The major area of enhanced antigenicity is homologous to the spik e of canine parvovirus, an area known to contain both neutralizing and host-range determinants. Our data are consistent with a model in whic h the unique region of VP1 is necessary for the virus to assume its ma ture capsid conformation.