A monoclonal antibody generated against a recombinant peptide fragment of the B3 domain of carcinoembryonic antigen reacts with intact carcinoembryonic antigen

摘要

The chemical synthesis of a gene coding for a polypeptide of 77 amino acid residues (designated ceaB3) representing a fragment of the CEA-B3 domain of carcinoembryonic antigen (CEA) was achieved. The ceaB3 fragment was cloned into the plasmid pLZPWBI at the C-terminus of a derivative IacZMF of the lacZ gene, devoid of methionine and cysteine amino acid residues. The fusion protein lacZMF-ceaB3 represented approx. 30% of total proteins expressed after induction. The fusion protein was formed as inclusion bodies. Simple washing steps led to an insoluble fusion protein which was of approx. 80% purity. Another fusion gene was generated by inserting ceaB3 between the malE gene encoding maltose binding protein (mbp) and lacZα of the pmal-c2 vector. Expression of the resulting pmal-c2-ceaB3-lacZα yielded the fusion protein mbp-ceaB3-IacZα with a molecular mass of 57.94 kDa, which was obtained as a soluble protein in almost homogenous form after affinity chromatography employing amylopectin. Polyclonal sheep anti-CEA antiserum specifically reacted with fusion proteins lacZMF-ceaB3 and mbp-ceaB3-lacZα. A monoclonal antibody CEA/HK2 was generated employing lacZMF-ceaB3 for immunization and CEA for screening purposes. The mAB CEA/HK2 specifically recognized CEA in immunoblots. The described experimental strategy should be generally applicable for generation of fusion proteins. These fusion proteins are suitable for epitope characterization of existing antibodies, production of regiospecific polyclonal or monoclonal antibodies.