The use of sulfite to study the mechanism of membrane fusion induced by E1 of Semliki Forest virus.

In this study we have used 35S-labeled sulfite to modify the disulfide bonds of the proteins at the cell surface of Semliki Forest-infected Aedes albopictus cells before and after low pH treatment. This reagent specifically cleaves disulfide bonds and concomitantly reacts with the newly formed cysteines, thereby labeling the respective protein. Treatment of the infected cells with sulfite led to inhibition of the fusion activity only when applied after low pH exposure. These cells exhibited substantial incorporation of the label into the viral E1 glycoprotein as compared to the E2 glycoprotein. These results provide direct evidence for the low pH-induced conformational change of E1 during the generation of its fusogenic potential.