Recombinant Rubella Virus E2 protein

The two envelope glycoproteins of rubella virus (RV), E1 of 58 kDa and E2 of 42-47 kDa, were individually expressed in lepidopteran Spodoptera frugiperda as well as in Trichoplusia ni insect cells using baculovirus vectors. The authentic signal sequences of E1 and E2 were replaced with the honeybee melittin signal sequence, allowing efficient entrance into the secretory pathway of the insect cell. In addition, the hydrophobic transmembrane anchors at the carboxyl termini of E1 and E2 proteins were removed to enable secretion rather than maintenance in the cellular membranes. Synthesis of the recombinant proteins in the absence and presence of tunicamycin revealed that both E1 and E2 were glycosylated with apparent molecular weights of 52 kDa and 37 kDa, respectively. Recombinant E2 appeared to be partially secreted, whereas E1 was essentially found inside the infected insect cell. The E1 protein was produced in large scale using a 10-1 bioreactor and serum-free medium (SFM). Purification of the recombinant protein product was performed from cytoplasmic extracts by ammonium sulphate precipitation followed by Concanavalin A affinity chromatography. This type of purified recombinant viral glycoproteins may be useful not only in diagnostic medicine or for immunization, but should enable studies designed to solve the structure of the virus particle.

Two rubella virus DNA vaccines were constructed from a cDNA clone of the rubella virus genomic RNA, one which contained the coding sequences for all three virion proteins (C, E2. and El) and one which contained the two envelope glycoproteins (E2 and El). When used to immunize mice via gene gun delivery, both constructs induced an antibody response of equivalent titer to that induced by rubella virus that persisted for at least seven months. A booster injection given four weeks after the initial injection increased antibody titers by over thirty-fold. The antibody response in DNA vaccine-injected mice was directed primarily against the El glycoprotein, as was the case in rubella virus-injected mice, and neutralizing activity was detected. These DNA vaccines are thus prototypes for a nonreplicating rubella virus vaccine that could be used in specialized circumstances. (C) 1999 Elsevier Science Ltd. All rights reserved.