title: The catalytic site structural gate of adenosine deaminase allosterically modulates ligand binding to adenosine receptors.
abstract: The enzyme adenosine deaminase (ADA) is a multifunctional protein that can both degrade adenosine and bind extracellularly to adenosine receptors, acting as an allosteric modulator regulating the hormonal effects of adenosine. The molecular regions of ADA responsible for the latter are unknown. In this work, alanine scanning mutagenesis of various ADA amino acid stretches, selected through in silico docking experiments, allowed us to identify regions of the enzyme responsible for modulating both its catalytic activity and its ability to modulate agonist binding to A and A adenosine receptors (AR and AR). The combination of computational and in vitro experiments show that the structural gate to the catalytic site; i.e., the α-1 helix containing residues L58-I72 and the loop containing residues A184-I188 of ADA, were important to maintain both the catalytic efficiency of the enzyme and its action as an allosteric modulator of the adenosine receptors. These data are consistent with a predicted supramolecular assembly, in which ADA bridges AR and CD26 and are in line with the notion that the interaction of ADA with adenosine receptors has an important role in the immunosynapse. We propose that it is the ADA open form, but not the closed one, that is responsible for the functional interaction with A₁R and A₂AR.
authors.affiliation: Laboratory of Molecular Neurobiology, Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Av. Diagonal 643, 08028 Barcelona, Spain.
authors.forename: Eduard
authors.initials: E
authors.lastname: Gracia
authors.forename: Daniel
authors.initials: D
authors.lastname: Farré
authors.forename: Antoni
authors.initials: A
authors.lastname: Cortés
authors.forename: Carles
authors.initials: C
authors.lastname: Ferrer-Costa
authors.forename: Modesto
authors.initials: M
authors.lastname: Orozco
authors.forename: Josefa
authors.initials: J
authors.lastname: Mallol
authors.forename: Carme
authors.initials: C
authors.lastname: Lluís
authors.forename: Enric I
authors.initials: EI
authors.lastname: Canela
authors.forename: Peter J
authors.initials: PJ
authors.lastname: McCormick
authors.forename: Rafael
authors.initials: R
authors.lastname: Franco
authors.forename: Francesca
authors.initials: F
authors.lastname: Fanelli
authors.forename: Vicent
authors.initials: V
authors.lastname: Casadó
mesh_terms: D000243:Adenosine Deaminase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000494:Allosteric Regulation / Q000502:physiology; D006801:Humans; D062105:Molecular Docking Simulation; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D011485:Protein Binding; D017433:Protein Structure, Secondary; D043682:Receptor, Adenosine A1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D043705:Receptor, Adenosine A2A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D043682:Receptor, Adenosine A1; D043705:Receptor, Adenosine A2A; C548482:ADA protein, human; D000243:Adenosine Deaminase