A monoclonal antibody directed against the neurokinin-1 receptor contains a peptide sequence with similar hydropathy and functional properties to substance P, the natural ligand for the receptor

Monoclonal antibody (mAb) PS12, obtained using the complementary peptide me thodology, mimics the neuropeptide substance P (SP) in recognizing the SP-b inding domain of the neurokinin-l receptor (NK1R) and eliciting production of polyclonal antibodies cross-reacting with SP with a high affinity (Dery et al., 1997. J. Neuroimmunol. 76, 1-9). The aim of the present study was t o investigate which structural features of mAb PS12 might account for this molecular mimicry. Cloning and sequencing of variable regions of both light (VL) and heavy (VH) chains of this 'SP-like' antibody did not indicate any primary sequence homology between SP and any antibody region. Instead, the y revealed a striking similarity between the hydropathic profile of SP and that of an 11-amino-acid region in the light chain encompassing the second complementarity determining region (CDR2). When applied to CHO cells expres sing the human NK1R, a synthetic extended 17-amino-acid peptide (denoted CD R2L) corresponding to this VL region inhibited the high-affinity binding of radiolabeled SP and antagonized the SP-induced inositol phosphate producti on. Moreover, a re-examination of the sequences of several antibodies that previously served in the design of CDR-derived bioactive peptides indicated that these antibodies also carried the hydropathic image of the respective ligands that they mimic. In agreement with previous observations on artifi cial synthetic peptides, our data thus suggest that the molecular mimicry b etween natural proteins (i.e. antibody and hormone, for example) could be u nderstood on a structural level directly related, at least in part, to hydr opathic homology. These results could then guide the search for bioactive p aratope-derived peptides of potential pharmacological interest. We also obs erved inverse hydropathy between multiple CDRs of mAb PS12 (including CDR3H and CDR3L) and the peptide epitope, confirming the importance of hydropath ic complementarity in antigen-antibody interactions. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.