The effects of processing inhibitors of N-linked oligosaccharides on the intracellular migration of glycoprotein E2 of mouse hepatitis virus and the maturation of coronavirus particles.

We have studied the effects of tunicamycin and inhibitors of the processing of N-linked glycans including N-methyl-1-deoxynojirimycin, castanospermine, mannodeoxynojirimycin, and swainsonine on the transport of glycoprotein E2 and the intracellular maturation of the coronavirus mouse hepatitis virus A59. Indirect immunofluorescence staining with monoclonal antibodies revealed that glycoprotein E2 exhibits different antigenic properties depending on the presence and on the structure of the N-linked oligosaccharides and that efficient transport of glycoprotein E2 to the plasma membrane requires the removal of glucose residues. In the presence of tunicamycin in the nonglycosylated E2 apoprotein was synthesized in normal amounts and readily acylated throughout the infectious cycle. This E2-species could not be detected on the surface of mouse hepatitis virus A59-infected cells with indirect immunofluorescence staining or lactoperoxidase labeling. N-Methyl-1-deoxynojirimycin and castanospermine, both of which selectively inhibited the processing glucosidases, caused a drop in virion formation by two log steps and a drastic delay in the surface expression of glycoprotein E2. The E2 species synthesized under such conditions was acylated but accumulated intracellularly in a compartment distinct from the Golgi. Concomitantly, synthesis of the matrix glycoprotein E1 of mouse hepatitis virus A59 was drastically impaired. Mannodeoxynojirimycin and swainsonine, which block later stages of the processing pathway, had less or no effect on the transport of glycoprotein E2 and the formation of virus particles.