The structure of human parvovirus B19 at 8 A resolution

Empty capsids of the human parvovirus B19, self-assembled in a baculovirus expression system, have been crystallized in a cubic space group P2(1)3 with a = 362 A. In spite of extensive purifications, the crystals diffract X-rays to only 8.0 A resolution. Diffraction data were collected using oscillation photography with synchrotron radiation. The orientations of the particles in the unit cell were determined with a self-rotation function and their positions were obtained with an R-factor search using the known homologous canine parvovirus (CPV) structure. The resultant phases were improved by electron density averaging and solvent flattening to include all the terms between 23.0 and 8.0 A resolution. The central eight-stranded antiparallel beta-barrel, common to many viruses, is situated similarly in B19 with respect to the icosahedral symmetry axes to that observed for feline panleukopenia virus (FPV) and CPV. However, the surface structure of B19 is significantly different from the other known parvoviruses. The most striking difference is that B19 lacks the prominent spikes on the threefold icosahedral axes observed in FPV and CPV. This spike region contains residues involved in host recognition and antigenicity for the latter viruses, showing that there are major differences between subgroups of autonomous parvoviruses.