The structure of an individual pentamer of the murine polyomavirus VP1 protein. Each monomer is colored differently. The conformationally flexible C-terminal arms are shown here in conformations compatible with binding to neighboring molecules. Superposed is a fragment of the polyomavirus VP2 protein (white), which binds to a pentamer oriented toward the central cavity. VP1 is from PDB ID 1SIE; VP2 is from PDB ID 1CN3.