THE STRUCTURE OF PARVOVIRUSES

Capsids of autonomous parvoviruses are assembled from two proteins, VPI and VP2, which overlap in sequence, with VP1 having additional amino-terminal residues. Empty capsids can be assembled from VP2 alone. Post-translational cleavage of assembled particles can modify some of the proteins by truncation of a few of the amino-terminal residues of VP2 to generate VP3 in full virions. The structures of canine parvovirus (CPV) and feline panleukopenia virus (FPV) have been solved to better than 3.5 Angstrom resolution while the structure of human parvovirus, B19, has been determined to 8 Angstrom resolution only. In each case the T = 1 icosahedron is made up of 60 copies of a mixture of VP1, VP2 and VP3, where each subunit has a structural motif common to many other RNA and DNA viruses, consisting of an eight-stranded anti-parallel beta-barrel. The surface of the capsid is made up primarily of large elaborate loops which connect the beta-strands that make up the barrel. Variation, in the amino acid sequence and topology of these loops account for differing biological properties.