INTRACELLULAR PROCESSING AND ANTIGENIC MATURATION OF MEASLES-VIRUS HEMAGGLUTININ PROTEIN

The intracellular processing and antigenic maturation of the measles v irus (MV) hemagglutinin (H) protein in virus infected cells were probe d with murine monoclonal antibodies (Mabs) that reacted with continuou s and discontinuous epitopes. The antibodies distinguished between the immature, cotranslational monomeric form of the protein and the matur e, dimeric hemagglutinin structure. This was evidenced by testing of i mmunoreactivity of the Mabs with synthetic peptides, by in vitro synth esized H protein analysis, and by pulse-chase analysis of gel separate d monomeric and dimeric forms of the H protein. Time kinetics analysis showed that the protein was synthesized as monomers and most of them were converted into dimers with t(1/2) about 30 min. The H protein rem ained endoglycosidase H (Endo H) sensitive up to 30 min and started to acquire partial resistance to Endo H between 30 and 60 min (t(1/2) ab out 60 min) after synthesis. Oligomerization of the H protein was unaf fected in virus infected cells treated with a compound (carbonylcyanid e m-chlorophenylhydrazone, CCCP) that blocks transport from the endopl asmic reticulum (ER) to the Golgi complex. These results suggest that the H protein dimerization takes place in the ER before its transport to the medial Golgi complex. The Mabs specific for discontinuous epito pes reacted with the H protein in cells treated with CCCP. Thus confor mational antigenic epitope formation appears to take place in the ER.