IDENTIFICATION OF AMINO-ACIDS CONTROLLING THE LOW-PH-INDUCED CONFORMATIONAL CHANGE OF RABIES VIRUS GLYCOPROTEIN

The glycoprotein (G) of rabies virus assumes at least three different conformations: the native state detected at the viral surface above pH 7, the activated state involved in the first step of the fusion proce ss, and the fusion-inactive conformation (I). A new category of monocl onal antibodies (MAbs) which recognized specifically the I conformatio n at the viral surface has recently been described. These MAbs (17A4 a nd 29EC2) became neutralizing when the virus was preincubated at acidi c pH to induce the conformational change toward the I state of G. Muta nts escaping neutralization were then selected, In this study, we have investigated the fusion and the low-pH-induced fusion inactivation pr operties of these mutants. All of these mutants have fusion properties similar to those of the CVS parental strain, but five mutants (E282K, M44I, M44V, V392G, and M396T) were considerably slowed in their confo rmational change leading to the I state. These mutants allow us to def ine regions that control this conformational change. These results als o reinforce the idea that structural transition toward the I state is irrelevant to the fusion process, Other mutations in amino acids 10, 1 3, and 15 are probably located in the epitopes of selecting MAbs. Furt hermore, in electron microscopy, we observed a hexagonal lattice of gl ycoproteins at the viral surface of mutants M44I and V392G as well as strong cooperativity in the conformational change toward the I state. This finding demonstrates the existence of lateral interactions betwee n the spikes of a rhabdovirus.