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Human Adenosine A2A Receptor Binds Calmodulin with High Affinity in a Calcium-Dependent Manner

Piirainen, Henni, Hellman, Maarit, Tossavainen, Helena, Permi, Perttu, Kursula, Petri and Jaakola, Veli-Pekka (2015) Human Adenosine A2A Receptor Binds Calmodulin with High Affinity in a Calcium-Dependent Manner. Biophysical Journal, 108 (4). pp. 903-917.


Understanding how intracellular ligands bind to GPCRs and how binding changes receptor structure to affect signalling is critical for developing a complete picture of the signal transduction process. The adenosine A2A receptor (A2AR) is a particularly interesting example, as it has an exceptionally long intracellular carboxyl terminus, which is predicted to be mainly disordered. Experimental data on the structure of the A2AR C-terminus is lacking, since published structures of A2AR do not include the C-terminus. Calmodulin has been reported to bind to the A2AR C-terminus, with a possible binding site on helix 8, next to the membrane. The biological meaning of the interaction as well as its calcium dependence, thermodynamic parameters and organization of the proteins in the complex are unclear. Here, we characterized the structure of the A2AR C-terminus and the A2AR C-terminus-calmodulin complex using different biophysical methods, including native gel and analytical gel filtration, isothermal titration calorimetry, NMR spectroscopy, and small-angle X-ray scattering. We found that the C-terminus is disordered and flexible, and it binds with high affinity (Kd = 98 nM) to calmodulin without major conformational changes in the domain. Calmodulin binds to helix 8 of the A2AR in a calcium-dependent manner that can displace binding of A2AR to lipid vesicles. We also predicted and classified putative calmodulin binding sites in a larger group of G-protein-coupled receptors.

Item Type: Article
Keywords: intrinsically disordered, calorimetry, circular dichroism, NMR spectroscopy, solution structure, small-angle x-ray scattering
Date Deposited: 13 Oct 2015 13:11
Last Modified: 13 Oct 2015 13:11