Analysis of the protein-protein interactions in the parvovirus H-1 capsid.

The structure of the icosahedral capsid of the H-1 parvovirus was probed by chemical cross-linking methods. Treatment of empty capsids with high-molecular-weight polyethylene glycols resulted in irreversible aggregation of the minor capsid protein VP1. Multimers of VP1 containing at least five and perhaps six molecules were obtained, but only with empty capsids and not with the full, DNA-containing virus. Cross-linking of the empty capsids with dimethylsuberimidate confirmed the assignments of the products formed after treatment with polyethylene glycol. With dimethylsuberimidate the most abundant product was a heterologous dimer containing VP1 and the major capsid protein VP2'. A small amount of homologous VP2' dimer was also obtained, but the majority of VP2' remained unreacted even at high concentrations of dimethylsuberimidate. The capsid proteins of the full virus, on the other hand, were completely unreactive to dimethylsuberimidate. The data suggest that the minor protein VP1 may be clustered in the capsid and perhaps composes one or two of the morphological units of the icosahedral shell.