A bacterial signal peptide directs efficient secretion of eukaryotic proteins in the baculovirus expression system

Escherichia coli remains an organism of choice for the production of recombinant proteins required in large quantities. Whenever possible, secretion is the preferred strategy since it permits easy and efficient purification from the extracellular medium. Our efforts to use E. coli to secrete a human CD23 soluble variant fused to a pair of IgG binding domains via the Staphylococcal protein A signal peptide were unsuccessful. Surprisingly, when the same construct was expressed in the baculovirus system, efficient secretion was observed and cleavage of the signal peptide occurred at the expected site. Varying the genes in the fusions or the tags, or the topology of the gene and the tag, did not affect the high-level secretion and cleavage at the correct site. We envision that fusion of the bacterial signal sequence to eukaryotic recombinant genes will prove to be a tool of value for efficient protein secretion in insect cells using the baculovirus expression system.