Post-translational Processing and Oligomerization of the Fusion Glycoprotein of Human Respiratory Syncytial Virus

The post-translational maturation of the fusion protein (F) of human respiratory syncytial virus was investigated. Chemical cross-linking experiments indicated that F forms homotetramers and provided evidence that the intermonomer contacts involve primarily the F1 subunit. Homooligomerization as measured by sedimentation in sucrose gradients was insensitive to carbonyl cyanide m-chlorophenylhydrazone, indicating that it occurs in the endoplasmic reticulum. Cleavage of the F0 precursor to yield the F1 and F2 subunits was blocked by monensin or brefeldin A, indicating that it takes place in distal cisternae of the trans Golgi compartment or in the more distal trans Golgi network. The F0 precursor was not detected at the cell surface in surface immunoprecipitation experiments, indicating that cleavage is intracellular. The appearance of the cleaved F1 protein at the cell surface was concurrent with that of the attachment glycoprotein (G); this and other information indicated that the type 2 membrane orientation of G is not obligatorily associated with a reduced transit rate. Examination of F maturation in the presence of tunicamycin provided evidence that its expression at the cell surface depends upon cleavage and not directly upon glycosylation.