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Cryo-EM structures of adenosine receptor A₃AR bound to selective agonists.

ABSTRACT: The adenosine A₃ receptor (A₃AR), a key member of the G protein-coupled receptor family, is a promising therapeutic target for inflammatory and cancerous conditions. The selective A₃AR agonists, CF101 and CF102, are clinically significant, yet their recognition mechanisms remained elusive. Here we report the cryogenic electron microscopy structures of the full-length human A₃AR bound to CF101 and CF102 with heterotrimeric G_i protein in complex at 3.3-3.2 Å resolution. These agonists reside in the orthosteric pocket, forming conserved interactions via their adenine moieties, while their 3-iodobenzyl groups exhibit distinct orientations. Functional assays reveal the critical role of extracellular loop 3 in A₃AR's ligand selectivity and receptor activation. Key mutations, including His^3.37, Ser^5.42, and Ser^6.52, in a unique sub-pocket of A₃AR, significantly impact receptor activation. Comparative analysis with the inactive A_2AAR structure highlights a conserved receptor activation mechanism. Our findings provide comprehensive insights into the molecular recognition and signaling of A₃AR, paving the way for designing subtype-selective adenosine receptor ligands.

SUBMITTER: Cai H

PROVIDER: S-EPMC11021478 | biostudies-literature | 2024 Apr

REPOSITORIES: biostudies-literature

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Cryo-EM structures of adenosine receptor A3AR bound to selective agonists.

Cai Hongmin H Guo Shimeng S Xu Youwei Y Sun Jun J Li Junrui J Xia Zhikan Z Jiang Yi Y Xie Xin X Xu H Eric HE

Nature communications 20240416 1

The adenosine A3 receptor (A3AR), a key member of the G protein-coupled receptor family, is a promising therapeutic target for inflammatory and cancerous conditions. The selective A3AR agonists, CF101 and CF102, are clinically significant, yet their recognition mechanisms remained elusive. Here we report the cryogenic electron microscopy structures of the full-length human A3AR bound to CF101 and CF102 with heterotrimeric Gi protein in compl ...[more]

PMID: 38627384

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Project description:ABCG2 is a transporter protein of the ATP-binding-cassette (ABC) family that is expressed in the plasma membrane in cells of various tissues and tissue barriers, including the blood-brain, blood-testis and maternal-fetal barriers1-4. Powered by ATP, it translocates endogenous substrates, affects the pharmacokinetics of many drugs and protects against a wide array of xenobiotics, including anti-cancer drugs5-12. Previous studies have revealed the architecture of ABCG2 and the structural basis of its inhibition by small molecules and antibodies13,14. However, the mechanisms of substrate recognition and ATP-driven transport are unknown. Here we present high-resolution cryo-electron microscopy (cryo-EM) structures of human ABCG2 in a substrate-bound pre-translocation state and an ATP-bound post-translocation state. For both structures, we used a mutant containing a glutamine replacing the catalytic glutamate (ABCG2EQ), which resulted in reduced ATPase and transport rates and facilitated conformational trapping for structural studies. In the substrate-bound state, a single molecule of estrone-3-sulfate (E1S) is bound in a central, hydrophobic and cytoplasm-facing cavity about halfway across the membrane. Only one molecule of E1S can bind in the observed binding mode. In the ATP-bound state, the substrate-binding cavity has collapsed while an external cavity has opened to the extracellular side of the membrane. The ATP-induced conformational changes include rigid-body shifts of the transmembrane domains, pivoting of the nucleotide-binding domains (NBDs), and a change in the relative orientation of the NBD subdomains. Mutagenesis and in vitro characterization of transport and ATPase activities demonstrate the roles of specific residues in substrate recognition, including a leucine residue that forms a 'plug' between the two cavities. Our results show how ABCG2 harnesses the energy of ATP binding to extrude E1S and other substrates, and suggest that the size and binding affinity of compounds are important for distinguishing substrates from inhibitors.

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Cryo-EM structures of adenosine receptor A₃AR bound to selective agonists.

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Cryo-EM structures of adenosine receptor A<sub>3</sub>AR bound to selective agonists.

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