A FUSION PLASMID FOR THE SYNTHESIS OF LIPOPEPTIDE-ANTIGEN CHIMERAS IN ESCHERICHIA-COLI

Lipopeptides are potential vaccine candidates with a built-in adjuvant property. To circumvent the present chemical route of synthesis for lipopeptide-antigen conjugates, the lipoprotein property of the pColE2-P9-encoded lysis protein, CelB, was used to create the bacterial fusion plasmid, pKLY3, to produce lipopeptide-antigen chimeras in Escherichia coli. Plasmid pKLY3 is a derivative of pKK233-2 with the origin of replication of the single-stranded DNA phase, fl. Under control of the promoter, p(trc), is the 5' end of the celB gene coding for a lipoprotein signal peptide and the first five amino acids (aa) (CQANY) of the mature lysis protein. As model systems for the synthesis of small and large lipopeptide-antigens, DNA sequences coding for the P2 peptide and E. coli alkaline phosphatase (PhoA) were fused in frame to the region of celB coding for a lipoprotein signal peptide and CQANY. P2 is a 12-aa peptide including a tyrosine phosphorylation site of the epidermal growth factor receptor (EGF-R). Inducible expression of stable lipohexapeptide CQANYV, lipo-CQANY-P2, and lipo-CQANYA-PhoA, was demonstrated. Similar expression was obtained for lipo-CIEGR-P2 and lipo-CIEGRA-PhoA in which IEGR is a cleavage recognition site for the blood coagulation factor, X(a). Like QANY, IEGR is predicted to form a beta-turn structure. The presence of a lipid moiety on the products was confirmed by demonstrating the incorporation of radioactive palmitic acid and inhibition of processing by globomycin. The lipid-modified peptides were also identified by incorporation of radioactive tyrosine, and the nature of the P2 peptide was verified immunologically. The enzyme portion of the lipopeptide-PhoA chimeras was presented in the periplasm in an active form. Cellular fractionation showed that lipid-modified P2 and PhoA are mainly associated with the outer membrane fraction of the E. coli cells.