Expression of the S1 sub-unit of pertussis toxin using a recombinant baculovirus

The full-length genome of the S1 sub-unit containing the native signal sequence was inserted downstream of the polyhedrin promoter of Autographa californica nuclear polyhedrosis virus. A large amount of 28 Kd protein, which was larger than the authentic S1 sub-unit (26 Kd), was detected in insect cells infected with the recombinant virus by Coomassie blue staining after resolving by SDS-PAGE. Although the level of expression of the recombinant S1 sub-unit was high, immunoblotting and N-terminal sequencing analyses of the expressed product revealed that the signal sequence of the S1 was poorly processed in the insect cells. In vitro assembly of the recombinant S1 sub-unit with native B oligomer to form holotoxin was low, based on an estimation of both cell cytotoxicity against Chinese hamster ovary (CHO) cells and binding activity to haptoglobin and anti-B oligomer antibody.