STRUCTURE OF MURINE POLYOMAVIRUS COMPLEXED WITH AN OLIGOSACCHARIDE RECEPTOR FRAGMENT

THE polyomaviruses are non-enveloped, icosahedrally symmetrical partic les with circular double-stranded DNA genomes(1,2). The outer shell of the virion contains 360 copies of viral protein VP1 (M(r) similar to 42K) arranged in pentamers(3). We report here the structure at 3.65 An gstrom resolution of murine polyomavirus ('polyoma') complexed with an oligosaccharide receptor fragment. This structure has been determined using the previously described model of simian virus 40 (SV40)(4). Al though very similar in structure to SV40, polyoma has interesting biol ogical differences. Cell-surface N-acetyl neuraminic acid (sialic acid ) is required for polyoma infectivity, but not for SV40. Polyoma attac hes to the surface of susceptible cells by stereospecific recognition of oligosaccharides terminating in (alpha 2,3)-linked sialic acid(5,6) . Studies of pathogenicity show that the specificity of viral binding to such oligosaccharides is an important determinant of the virus' abi lity to establish a disseminated infection and to induce tumours in th e natural host. The complex described here shows how polyoma recognize s the receptor fragment and how strains with different receptor specif icities can distinguish between alternative ligands. The results also suggest an explanation for the large disparity in pathogenicity exhibi ted by strains differing in only one amino-acid residue of Vp1(7,8).