INTERACTION OF POLYOMAVIRUS INTERNAL PROTEIN VP2 WITH THE MAJOR CAPSID PROTEIN VP1 AND IMPLICATIONS FOR PARTICIPATION OF VP2 IN VIRAL ENTRY

A complex of the polyomavirus internal protein VP2/VP3 with the pentam eric major capsid protein VPI has been prepared by co-expression in Es cherichia coli, A C-terminal segment of VP2/VP3 is required for tight association, and a crystal structure of this segment, complexed with a VPI pentamer, has been determined at 2,2;Angstrom resolution. The str ucture shows specific contacts between a single copy of the internal p rotein and a pentamer of VP1, These interactions were not detected in the previously described structure of the virion, but the location of VP2 in the recombinant complex is consistent with features in the viri on electron-density map. The C-terminus of VP2/VP3 inserts in an unusu al, hairpin-like manner into the axial cavity of the VP1 pentamer, whe re it is anchored strongly by hydrophobic interactions, The remainder of the internal protein appears to have significant flexibility. This structure restricts possible models for exposure of the internal prote ins during viral entry.