Protein Expression and Purification, Vol.124, 62-67, 2016
Impact of purification conditions and history on A(2A) adenosine receptor activity: The role of CHAPS and lipids
The adenosine A(2A) receptor (A(2A)R) is a much-studied class A G protein-coupled receptor (GPCR). For biophysical studies, A(2A)R is commonly purified in a detergent mixture of dodecylmaltoside (DDM), 3-(3-cholamidopropyl) dimethylammoniopropane sulfonate (CHAPS), and cholesteryl hemisuccinate (CHS). Here we studied the effects of CHAPS on the ligand binding activity and stability of wild type, full-length human A(2A)R. We also tested the cholesterol requirement for maintaining the active conformation of the receptor when solubilized in detergent micelles. To this end, the receptor was purified using DDM, DDM/CHAPS, or the short hydrocarbon chain lipid 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC, di6:0PC). After solubilization in DDM, DDM/CHAPS, or DHPC micelles, although A(2A)R was found to retain its native-like fold, its binding ability was significantly compromised compared to DDM or DDM/CHAPS with CHS. It therefore appears that although cholesterol is not needed for A(2A)R to retain a native like, a-helical conformation, it may be a critical component for high affinity ligand binding. Further, this result suggests that the conformational differences between the active and inactive protein may be so subtle that commonly used spectroscopic methods are unable to differentiate between the two forms, highlighting the need for activity measurements. The studies presented in this paper also underline the importance of the protein's purification history; i.e., detergents that interact with the protein during purification affect the ligand binding properties of the receptor in an irreversible manner. (C) 2016 Elsevier Inc. All rights reserved.