Identification in the NK1 tachykinin receptor of a domain involved in recognition of neurokinin A and septide but not of substance P

The three mammalian tachykinins, substance P (SP), neurokinin A (NKA) and n eurokinin B (NKB), exert their physiological effects through specific recep tors, NK1, NK2 and NK3, respectively. However, homologous binding studies h ave recently demonstrated that, contrary to the generally accepted belief, NKA could bind NK1 receptor with high affinity (Hastrup and Schwartz, 1996) , Using COS-7 cells expressing the human NK1 receptor, me show that two sim ultaneous point mutations (E193L and V195R) in a restricted five amino acid sequence (the (193-197) region), selected because of its hydropathic compl ementarity with the common C-terminal extremity of tachykinins, abolish bot h the high-affinity binding and highly potent biological activity of NKA, w ithout affecting those of SP, In addition, the same mutations also suppress ed the high functional activity of septide, a synthetic SP atypical agonist ([pGlu(6)-Pro(9)] SP 6-11), These results suggest that the (193-197) regio n, located at the end of the second extracellular loop of the receptor, cou ld be part of a common high-affinity binding domain for both NKA and septid e, distinct from the SP binding site. (C) 1999 Federation of European Bioch emical Societies.