Epitope mapping for the anti-rabbit cholesteryl ester transfer protein monoclonal antibody that selectively inhibits triglyceride transfer

Among the monoclonal antibodies (Mab) against rabbit plasma cholesteryl est er transfer protein (CETP), Mab 14-8F cross-reacted with human CETP and sel ectively inhibited triglyceride transfer but not cholesteryl ester transfer (Ko, K. W. S., T. Ohnishi, and S. Yokoyama. 1994.J. Biol. Chem. 269: 28206 -28213), The epitope of this antibody was studied by using synthetic fragme nt peptides of rabbit and human CETP, Mab 14-8F reacted with the peptide R4 51-Q473 of human CETP near the carboxl-terminal and not with the peptides r epresenting any other regions, and inhibited the binding of human CETP to t he goat antibody against its carboxyl 1-terminal peptide R451-S476, The exp eriments with a series of the fragment peptides in this region revealed tha t the epitope requires the segment 465-473 (EHLLVDFLQ) of human CETP or 485 -493 (KHLLVDFLQ) Of rabbit CETP (core epitope) though neither peptide by it self binds to the antibody Both peptides needed extension at least by one r esidue beyond either amino- or carboxyl-end in order to show the reactivity to the antibody, but the effect was not highly residue-specific at least a t the amino-end. Circular dichroism analysis demonstrated the increase of h elical conformation by the extension of the "core epitope'' peptides to eit her direction. Thus, the epitope is dependent on conformation of the core e pitope induced by the presence of an additional residue(s) in either end, T he core epitope occupies the central 64% of the reported linear epitope of Mab TP2, a widely used anti-human CETP monoclonal antibody that inhibits bo th cholesteryl ester and triglyceride transfer. Therefore, we conclude that the Limited interaction of Mab with a common lipid interaction site causes selective inhibition of the transfer of triglyceride that has presumably l ower priority than cholesteryl ester for the CETP reaction.