title: Role of the second transmembrane domain of rat adenosine A1 receptor in ligand-receptor interaction.
abstract: Initial mutagenesis studies exploring the ligand recognition model of A1 adenosine receptor (A1R) mainly focused on the residues in the 5th-7th transmembrane domains (TMs5-7). Little is known about the role of residues in TM2. To explore the importance of reserved hydrophobic region in TM2 of A1R, we mutated the hydrophobic residues at positions 65 and 69 to hydrophilic residues (L65T, Leu-65 to Thr-65; I69T, Ile-69 to Thr-69; I69S, Ile-69 to Ser-69) to change the hydrophobicity at the outer end of TM2. Binding assays showed that the affinities of mutant receptors were significantly decreased for ribose group-containing agonists (2-chloro-N6-cyclopentyladenosine (CCPA) and 5'-N-ethyl-carboxamidoadenosine (NECA)) but not for antagonists, N6-cyclopentyl-9-methyladenine (N-0840), an adenine derivative lacking ribose group, and 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX), a xanthine derivative. This observation suggests that the hydrophobic region at the outer end of TM2 may mediate the recognition of the ribose group of CCPA and NECA.
authors.affiliation: Department of Pharmacology, Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 201203, PR China.
authors.forename: Ke-Qiang
authors.initials: KQ
authors.lastname: Xie
authors.forename: Yan
authors.initials: Y
authors.lastname: Cao
authors.forename: Xing-Zu
authors.initials: XZ
authors.lastname: Zhu
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D000241:Adenosine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D058907:Adenosine A1 Receptor Agonists; D058916:Adenosine A1 Receptor Antagonists; D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D017434:Protein Structure, Tertiary; D051381:Rats; D043682:Receptor, Adenosine A1 / Q000737:chemistry*; D014970:Xanthines / Q000737:chemistry / Q000378:metabolism
chemical_list: D058907:Adenosine A1 Receptor Agonists; D058916:Adenosine A1 Receptor Antagonists; D008024:Ligands; D043682:Receptor, Adenosine A1; D014970:Xanthines; C080758:N(6)-cyclopentyl-9-methyladenine; D019830:Adenosine-5'-(N-ethylcarboxamide); C058394:2-chloro-N(6)cyclopentyladenosine; C051360:1,3-dipropyl-8-cyclopentylxanthine; D000225:Adenine; D000241:Adenosine