The Extracellular Loop 2 (ECL2) of the Human Histamine H4 Receptor Substantially Contributes to Ligand Binding and Constitutive Activity

• DOI: 10.1371/journal.pone.0117185
• Publication Date: 2015-01-28T18:59:24Z
• Authors: David Wifling; Günther Bernhardt; Stefan Dove; Armin Buschauer
• Keywords: Inverse agonist; Thioperamide

In contrast to the corresponding mouse and rat orthologs, human histamine H4 receptor (hH4R) shows extraordinarily high constitutive activity. extracellular loop (ECL), replacement of F169 by V as in H4R significantly reduced Stabilization inactive state was even more pronounced for a double mutant, which, addition F169V, S179 ligand binding site replaced M. To study role FF motif ECL2, we generated hH4R-F168A mutant. The co-expressed Sf9 insect cells with G-protein subunits Gαi2 Gβ1γ2, membranes were studied [3H]histamine functional [35S]GTPγS assays. potency various ligands at mutant decreased compared wild-type hH4R, example 30- than 100-fold case agonist UR-PI376 histamine, respectively. activity hH4R completely lost reflected neutral antagonism thioperamide, full inverse hH4R. By analogy, JNJ7777120 partial but again demonstrating decrease due F168A mutation. Thus, F168 proven play key not only potency, also