Oligomerization of N-terminal domain of carcinoembryonic antigen (CEA) expressed in Escherichia coli.

The N-terminal domain of CEA, which is essential for cell adhesion activity and lacks cysteine residue, was expressed in Escherichia coli and purified from the solubilized inclusion bodies by DEAE-Sepharose and gel filtration chromatographies. The purified N-domain migrated in SDS-PAGE as a single 13-kDa band, whereas it migrated in non-SDS-PAGE as five distinct bands. The N-domain, analyzed by two-dimensional PAGE after cross-linking with DSS, migrated in multiple forms ranging from monomer to pentamer, showing unequivocally the presence of multimers in each band. The amount of monomer was distinctively the least among the oligomers in the non-SDS-PAGE. These results suggest that the N-domain of CEA molecule has a strong tendency to self-assemble that may convey the homophilic cell adhesion of CEA.