FOLDING OF RABIES VIRUS GLYCOPROTEIN - EPITOPE ACQUISITION AND INTERACTION WITH ENDOPLASMIC-RETICULUM CHAPERONES

Four well-characterized monoclonal antibodies (MAbs) directed against rabies virus glycoprotein (G) were used to study G folding in vivo. Tw o of the MAbs were able to immunoprecipitate incompletely oxidized fol ding intermediates, The two others recognized G only after folding was completed, By using these MAbs, the ability of G to undergo low-pH-in duced conformational changes during folding was also investigated, It appeared that some domains acquire this ability before folding is comp leted, In addition, interactions between unfolded G and some of the mo lecular chaperones mere analyzed, Unfolded G was associated with BiP a nd calnexin, Association with BiP was maximal immediately after the pu lse, whereas association with calnexin was maximal after 5 to 10 min o f chase. The effects of tunicamycin and castanospermine on chaperone b inding and folding were also studied, In the presence of both drugs, c alnexin binding was reduced, consistent with the view that calnexin sp ecifically recognizes monoglucosylated oligosaccharides, but some resi dual binding was still observed, indicating that calnexin also recogni zes the polypeptide chain, In the presence of both drugs, association with BiP was increased and prolonged and folding was impaired, However , the global effects of the drugs were different, since folding was mu ch more efficient in the presence of castanospermine than in the prese nce of tunicamycin. Taken together, these results provide the basis to draw a schematic view of rabies virus glycoprotein folding.