Cell Discovery: Revealing the molecular mechanism by which adenosine receptor A2BR binds endogenous and selective ligands

Adenosine (ADO) is widely distributed in various tissues and organs of the human body, and regulates a variety of important physiological and pathological processes
in the human body by acting on adenosine receptors (ARs).
The ARs family includes four subtypes, A1R, A2AR, A2BR, and A3R, with A2BR having a weak affinity for the adenosine molecule (micromolar level) and the other three receptors binding at the nanomolar level
.
A2BR is expressed in immune cells, fibroblasts, smooth muscle cells and a variety of tumor cells, regulating immunity, cell growth, heart function, etc
.
The adenosine/A2BR signaling pathway has a histoprotective effect in acute disease models, such as myocardial ischemia and acute lung injury
.
The small molecule non-nucleoside ligand BAY 60-6583 is a high-affinity selective agonist of A2BR with cardioprotective effects
.

Recently, Xu Huaqiang's team, a researcher at the Shanghai Institute of Materia Medica, Chinese Academy of Sciences, and Jiang Yi, a co-researcher in the team of researcher Xie Xin, jointly published the latest research results
in Cell Discovery with the title of Structures of adenosine receptor A2BR bound to endogenous and synthetic agonists 。 The cryo-EM structure of the A2BR receptor family binding to endogenous ligand adenosine (ADO) and selective agonist small molecules (BAY 60-6583) and coupling the modified Gs complex with resolutions of 3.
2 angstroms and 2.
9 angstroms
, respectively was resolved.

The study showed that A2BR has highly conserved adenosine ligand-binding pockets
compared to the adenosine receptor family.
Molecular dynamics simulations show that the binding of ADO to A2BR ligand-recognition pockets has lower stability than A1R and A2AR, which may mediate the relatively low affinity
of ADO for A2BR.
Compared to endogenous ADO, BAY 60-6583 has a deeper binding site and forms polar interactions
with amino acids deep in the pocket.
By analyzing the difference between ligand-binding pocket residues in the adenosine family receptor, the researchers found that the 6.
51-position valine (V6.
51) in the A2BR pocket, while the other members of the adenosine receptor family were all leucine (L6.
51)
at that site.
Leucine has a longer side chain than valine and may cause steric hindrance
on ligand binding.
The researchers reversed mutations at the 6.
51 site of A1R/A2AR and found that these mutants all acquired the ability to bind BAY 60-6583 molecules, suggesting that the 6.
51-position valine is a key site for A2BR binding selective
ligands.
The results of this study helped researchers understand the mechanism of A2BR binding to adenosine and non-nucleoside ligands from the perspective of structure, and laid a structural foundation
for the selective ligand development of adenosine family receptors.

Figure 1 a-b.
ADO and BAY 60-6583 complex structures with A2BR and GS proteins; e.
Kinetic simulation of adenosine receptor binding to adenosine pockets; f.
adenosine receptor family regular pocket amino acids; g.
potential steric steric hindrance between BAY 60-6583 and L6.
51; h.
Effect
of leucine/valine at position 6.
51 for wild-type and mutant ARs on BAY 60-6583.