Processing of HBsAg expressed by variceela-zosten virus

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Hepatitis B surface antigen (HBsAg) was expressed by varicella-zoster virus (VZV) and morphogenesis of expressed HBsAg particles was studied by using metabolic inhibitors. HBsAg was modified by N-linked and O-linked glycosylation, and sialylation, and these were used for the markers of glycosylation process in the morphogenesis of HBsAg. Transmission and immunoelectron microscopic observations were used to identify the subcellular localization of HBsAg and HBsAg particle formation. Biochemical and morphological results were used to construct a model for morphogenesis of HBsAg particles. HBsAg was synthesized as 26K protein in the rough endoplasmic reticulum (ER) and then the high mannose glycan was added to form 30K protein. Three kinds of dimers with disulfide bonds 26K-26K, 26K-30K, and 30K-30K, were transported into the cytoplasmic vacuoles of the cis Golgi area. HBsAg particles were formed by the assembly of HBsAg in the cytoplasmic vacuoles and were not formed by budding or extrusion of transmemrane precursor containing HBsAg into the lumen of the ER.HBsAg particles in the vacuoles were further processed by glycosylation enzymes in the Golgi apparatus during transport to the cell surface by the cytoplasmic vacuolar flow ; conversion from the high mannose glycan to the complex type glycan, O-linked glycosylation, and sialylation in both glycans. Then fully processed HBsAg particles composed of 30K-30K, 30K-35K, and 35K-35K dimers were secreted into extracellular space possibly by exocytosis. Thus HBsAg particles expressed by VZV had novel features in its morphogenesis and glycosylation.