Expression of the spike protein of murine coronavirus JHM using a baculovirus vector

The spike (S) protein of murine coronavirus JHM strain (JHMV) has been expressed in insect cells using a recombinant baculovirus vector. The expressed S protein was shown to be glycosylated and expressed on the cell surface, and to be similar in size and antigenic properties to the S protein produced in mouse cells infected by JHMV. However, no proteolytic cleavage was detected in insect cells. The sera from rats immunised with S protein derived from insect cells reacted in immunoprecipitation and immunofluorescence with the S protein produced in JHMV-infected mouse cells. However, the antisera failed to neutralize the infectivity of JHMV. The studies on two proteins expressed by recombinant baculoviruses, corresponding to the cleavage products S1 and S2, and a panel of monoclonal antibodies suggest that the majority of epitopes which elicit the neutralizing antibodies are present in the N terminal half of the S protein.