Identification of residues involved in neurotensin binding and modeling ofthe agonist binding site in neurotensin receptor 1

The neurotensin receptor 1 (NTR1) subtype belongs to the family of G protei n-coupled receptors and mediates most of the known effects of the neuropept ide including modulation of central dopaminergic transmission. This suggest ed that nonpeptide agonist mimetics acting at the NTR1 might be helpful in the treatment of Parkinson's disease and schizophrenia. Here, we attempted to define the molecular interactions between neurotensin-(8-13), the pharma cophore of neurotensin, and the rat NTR1, Mutagenesis of the NTR1 identifie d residues that interact with neurotensin, Structure-activity studies with neurotensin-(8-13) analogs identified the peptide residues that interact wi th the mutated amino acids in the receptor. By taking these data into accou nt, computer-assisted modeling techniques were used to build a tridimension al model of the neurotensin-(8-13)-binding site in which the N-terminal tet rapeptide of neurotensin(8-13) fits in the third extracellular loop and the C-terminal dipeptide binds to residues at the junction between the extrace llular and transmembrane domains of the receptor. Interestingly, the agonis t binding site lies on top of the previously described NTR1-binding site fo r the nonpeptide neurotensin antagonist SR 48692, Our data provide a basis for understanding at the molecular level the agonist and antagonist binding modes and may help design nonpeptide agonist mimetics of the NTR1.