REACTIVITY OF ANTIBODIES TO HETEROCLITIC PEPTIDES BASED ON THE CHLAMYDIA-TRACHOMATIS MAJOR OUTER-MEMBRANE PROTEIN

One problem of peptide vaccines is that antibodies generated against t hem react poorly with the target sequence on the native protein. Using monoclonal antibodies (mAbs) to the serovar L1 type-specific epitope on the major outer-membrane protein of Chlamydia trachomatis as our mo del in conjunction with the Pin Technology Epitope Scanning technique, we had previously identified the critical binding site at this epitop e as DAVP. Amino acid substitution showed that AV were essential resid ues for binding. A series of structurally related (heteroclitic) pepti des retaining AV were synthesized. Some of these were found to be much more reactive with the model mAb than peptides of cognate sequence. I t was hypothesized that the DAVP peptide only approximated to the conf ormation of the homologous sequence in the native protein, whereas som e of the flexible heteroclitic peptides produced conformations which m ore closely resembled the native constrained sequence. The key questio n was whether the most reactive heteroclitic peptide would also genera te antibody capable of more efficient binding to the native protein. W e therefore immunized mice with one of six heteroclitic peptides or on e of two native sequence control peptides. The reactivity of these ant isera with the peptide immunogens and with native chlamydial elementar y bodies was then evaluated by enzyme immunoassay. Pooled antisera to two of the heteroclitic peptides reacted with significantly greater ab sorbance (P < 0.05) and at higher dilution with whole chlamydiae than did pooled antisera to the control peptides. This suggests that hetero clitic peptides may in some circumstances be useful to increase the re activity of site-specific antibodies with epitopes on the native prote in important for vaccine development or for serodiagnosis.