Orexin/hypocretin receptor chimaeras reveal structural features important for orexin peptide distinction

We wanted to analyze the basis for the distinction between OX1 and OX2 orexin receptors by the known agonists, orexin-A, orexin-B and Ala(11), D-Leu(15)-orexin-B, of which the latter two show some selectivity for OX2. For this, chimaeric OX1/OX2 and OX2/OX1 orexin receptors were generated. The receptors were transiently expressed in HEK-293 cells, and potencies of the agonists to elicit cytosolic Ca2+ elevation were measured. The results show that the N-terminal regions of the receptor are most important, and the exchange of the area from the C-terminal part of the transmembrane helix 2 to the transmembrane helix 4 is enough to lead to an almost total change of the receptor's ligand profile. (C) 2011 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.