Expression and characterization of a soluble rubella virus E1 envelope protein.

Individual specific antigenic rubella virus (RV) structural proteins are required for accurate serological diagnosis of acute and congenital rubella infections as well as rubella immune status. The RV envelope glycoprotein E1 is the major target antigen and plays an important role in viral-specific immune responses. The native virion is difficult to produce in large quantities and the protein subunits are also difficult to isolate without loss of antigenicity. The production of a soluble RV E1 (designated E1 delta Tm) using the baculovirus-insect cell expression system is described. In contrast to wild-type RV E1, the genetically engineered E1 delta Tm protein lacks a transmembrane anchor. It behaved as a secretory protein and was secreted abundantly from insect cells. Pulse-chase studies were used to examine the synthesis, glycosylation, and secretion of E1 delta Tm by the insect cells. The secreted E1 delta Tm protein was purified from serum-free medium by one-step immunochromatography. The purified E1 delta Tm protein retained full antigenicity and may be a convenient source of E1 protein for use in diagnostic assay and rubella vaccine development.