Effects of E2 and E1 glycosylation on specific membrane fusion in rubella virus strain JR23

To explore the effects of glycosylation in glycoprotein on membrane fusion in rubella virus strain JR23.

The N-linked glycosylation sites in glycoproteins were mutated individually or in combination. Total expression and cell surface expression efficiencies of mutant proteins were assayed with Western blot and FACS. The fusion functions were assayed with Giemsa staining and reporter gene method. Binding activity of mutant proteins was detected with hemadsorption assays.

We observed that total expression levels of all the mutant proteins in cells were unchanged, but the cell surface expression efficiencies of all the mutant proteins except E2 S131V were lower than wild-type protein. When effects of reduced cell surface expression were eliminated, mutant proteins N53G, S73I, S131V and T78A had lower fusion activities than wild-type protein, and binding abilities of E2 S73I and E1 T78A decreased slightly. But in all the combined mutants, no cell fusion was detected, and only a minor hemadsorption was observed in N53G-S131V, N53G-T78A and N53G-T211A.

Glycosylation of glycoproteins were involved in cell surface expression synergistically. Glycosylation on E2 N53, N71, N129 and E1 N76 altered the specific membrane fusion, whereas no effects were detected on E1 N177 and N209 individually.