Recent high resolution structures of modified G-protein coupled receptors (GPCRs) have provided major insight into the mechanisms of receptor-ligand binding. However understanding of the complete mechanism of GPCR function remains limited. This study characterised C-terminally truncated versions of the human adenosine A(2A) receptor (A(2A)R) with a view to producing protein suitable for structural studies. The constructs terminated at residue A316, removing the intracellular C-terminal tail, or V334, producing a C-terminal tail equivalent in length to that of rhodopsin. Higher levels of functional receptor before and after solubilisation were obtained for both C-terminally truncated constructs compared to the wild-type receptor (WT) as assessed by radioligand binding analysis using [H-3]ZM241385. The construct which yielded the highest level of functional receptor, V334 A(2A)R, was purified in DDM to high homogeneity with a final yield of 2 mg/L. Binding analysis revealed that the purified receptor had a specific activity of 20.2 +/- 1.2 nmol/mg, close to the theoretical maximum. Pure V334 A(2A)R was resistant to degradation over 15 days when stored at 4 degrees C or 20 degrees C and showed remarkable functional stability when stored at 4 degrees C, retaining 84% of initial functionality after 30 days. This construct is an excellent candidate for structural studies. (C) 2010 Elsevier Inc. All rights reserved.