Scanning mutagenesis in a yeast system delineates the role of the NPxxY(x)5,6F motif and helix 8 of the adenosine A2B receptor in G protein coupling

The adenosine receptor subfamily includes four subtypes: the A1, A2A, A2B and A3 receptors, which all belong to the superfamily of G protein-coupled receptors (GPCRs). The adenosine A2B receptor is the least investigated of the adenosine receptors, and the molecular mechanisms of its activation have hardly been explored. We used a single-GPCR-one-G protein yeast screening method in combination with mutagenesis studies, molecular modeling and bio-informatics to investigate the importance of the different amino acid residues of the NPxxY(x)6F motif and helix 8 in the human adenosine A2B receptor (hA2BR) activation. A scanning mutagenesis protocol was employed, yielding 11 single mutations and one double mutation of the NPxxY(x)6F motif and 16 single mutations of helix 8. The amino acid residues P2877.50, Y2907.53, R2937.56 and I3048.57 were found to be essential, since mutation of these amino acid residues to alanine led to a complete loss of function. Western blot analysis showed that mutant receptor R2937.56A was not expressed, whereas the other proteins were. Amino acid residues that are also important in receptor activation are: N2867.49, V2897.52, Y2927.55, N2948.47, F2978.50, R2988.51, H3028.55 and R3078.60. The mutation Y2907.53F lost 50% of efficacy, while F2978.50A behaved similar to wild type receptor. The double mutation, Y2907.53F/F2978.50Y, lost around 70% of efficacy and displayed a lower potency for the reference agonist 5′-(N-ethylcarboxamido)adenosine (NECA). This study provides new insight into the molecular interplay and impact of TM7 and helix 8 for hA2B receptor activation, which may be extrapolated to other adenosine receptors and possibly to other GPCRs.

Figure optionsDownload as PowerPoint slide