Structure of murine polyomavirus complexed with an oligosaccharide receptor fragment

THE polyomaviruses are non-enveloped, icosahedrally symmetrical particles with circular double-stranded DNA genomes1,2. The outer shell of the virion contains 360 copies of viral protein VP1 (Mr ˜42K) arranged in pentamers3. We report here the structure at 3.65 Å 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. Although very similar in structure to SV40, poly oma has interesting biological differences. Cell-surface N-ace-tyl neuraminic acid (sialic acid) is required for polyoma infectivity, but not for SV40. Polyoma attaches to the surface of susceptible cells by stereospecific recognition of oligosaccharides terminating in (α2,3)-linked sialic acid5,6. Studies of pathogenicity show that the specificity of viral binding to such oligosaccharides is an important determinant of the virus’ ability to establish a disseminated infection and to induce tumours in the natural host. The complex described here shows how polyoma recognizes the receptor fragment and how strains with different receptor specificities can distinguish between alternative ligands. The results also suggest an explanation for the large disparity in pathogenicity exhibited by strains differing in only one amino-acid residue of VP17,8.