Human endothelin receptor type A (ETA) is a G-protein coupled receptor that mediates vasoconstriction of blood vessels. To determine the structural characteristics and signaling mechanism of ETA, we have expressed recombinant ETA as a fusion protein with p9 envelope protein from phi6 bacteriophage. The His-tag-labeled p9-ETA fusion protein was highly expressed in the membrane fraction of Escherichia coli and purified to homogeneity by single affinity chromatography after solubilization with detergents. Purified p9-ETA appeared as an oligomer and presented mainly as an a-helical structure. The protein also showed specific binding to endothelin-1 (ET-1) and the alpha subunit of G(q) protein with apparent K-D values of 17 and 20 nM, respectively. An antagonist of ETA, bosentan, prevented the interaction between p9-ETA and ET-1 in a concentration-dependent manner. These results indicate that recombinant p9-ETA has a competent conformation for interactions with EF-1 and the alpha subunit of G(q) protein. (c) 2012 Elsevier Inc. All rights reserved.