Expression and characterization of secreted forms of Rubella virus E2 glycoprotein in insect cells

Abstract

Two different forms of rubella virus E2 glycoproteins were expressed in insect cells: intact wild-type E2 and a soluble form of E2 (E2ΔTm) glycoprotein, in which the C-terminal membrane-anchor domain was deleted. E2ΔTm behaved as a secretory protein and was secreted abundantly (5 mg/liter) from insect cells. In contrast to wild-type E2 (36 kDa), E2ΔTm was secreted into the media and was detected as two species (33 and 30 kDa). Lectin binding assays in conjunction with glycosidase analyses revealed that both intracellular wild-type E2 and E2ΔTm contained only N-linked glycans, while the two secreted forms of E2ΔTm were found to differ in their glycosylation, with the 30-kDa form having only Winked glycans while the 33-kDa species had both Winked and O-linked glycans. The secreted E2ΔTm species were purified by precipitation between 20 and 40% saturation with (NH 4) 2SO 4 and retained full antigenicity. The levels of antibodies elicited in mice immunized with purified E2ΔTm showed that the immunogenicity of secreted E2ΔTm compared favorably to that of natural virion E2.