MODELING OF THE RECOGNITION SITE OF THE NK1 RECEPTOR

The tachykinin receptor, NK1, and its native neuropeptide ligand, subs tance P, are believed to play a major role in the biochemistry of infl ammation and in the transmission of pain. The binding of substance P i s known to involve extracellular as well as transmembrane regions of t he NK1 receptor. Reported here is the design of a model of the recogni tion site of the second transmembrane domain of the NK1 receptor. Mole cular mechanics calculations were employed to evaluate the potential o f six polypeptides corresponding to the first, second and third transm embrane domains of the NK1 receptor, to bind with substance P. One of the most promising of these models contained 30 amino acid residues co rresponding to part of the first extracellular region coupled to the s econd transmembrane domain. A model of reduced size (18 amino acid res idues) that contains the correct type and location of the amino acid r esidues predicted to be involved in ligand binding was used to validat e the results of the molecular mechanics calculations. One-dimensional proton NMR spectra acquired in DMSO-d(6) indicated that this 18 amino acid residue polypeptide forms a complex with substance P.