The surface nature of proteins of a bovine enterovirus, before and after neutralization

The surface nature of the proteins of a bovine enterovirus have been determined by using 125I and pyridoxal phosphate-sodium borohydride labelling techniques. As found previously, 125I labels only VP1 in intact capsid particles, whereas reaction with pyridoxal phosphate followed by reduction with tritiated sodium borohydride labels VP1, VP2 and VP3. Only VP4 is found to have no surface tyrosine, histidine or lysine available for reaction. After neutralization with homologous antisera, however, VP4 becomes exposed and is then available for labelling with 125I. This must reflect a substantial conformational change in the virus particle after neutralization.