Agonist interactions with chimeric and mutant beta1- and beta3-adrenergic receptors: involvement of the seventh transmembrane region in conferring subtype specificity.
beta1- and beta3-adrenergic receptors (AR) are the predominant beta-AR subtypes in adipocytes, and analysis of native and recombinant beta-AR has revealed several pharmacological and biochemical differences between these subtypes. This study used chimeric and mutated rat beta-AR expressed in Chinese hamster ovary cells to examine the basis of certain characteristic differences in the agonist properties of catecholamines and prototypic beta3-AR agonists. The exchange of sequence beyond transmembrane (TM) region 6 between the beta-AR subtypes had dramatic and reciprocal effects on the affinity and efficacy of the prototypic beta3-AR agonists BRL 37,344 and CL 316,243, without affecting the interactions with catecholamines. Mutation of Phe350 and Phe351 in TM7 of the beta1-AR to Ala and Leu found in the beta3-AR was sufficient to allow activation by prototypic beta3-AR agonists. Interestingly, this mutation did not affect catecholamine action and it did not impair the ability of propranolol to block the actions of isoproterenol or the selective beta3-AR agonists. beta1-AR containing beta3-AR sequence from predicted TM5 through TM6 exhibited reduced affinity for catecholamines without altering agonist potency, suggesting enhanced coupling efficiency. Inclusion of the homologous beta1-AR sequence in the beta3-AR, however, did not produce reciprocal effects. These results are the first to define a major determinant of beta3-AR subtype-selective agonism in TM7 and demonstrate that the determinants of selective phenethanolamines, catecholamines, and propranolol action are distinct.
Granneman
J G
JG
Cellular and Clinical Neurobiology Program, Department of Psychiatry and Behavioral Neuroscience, Wayne State University School of Medicine Detroit, Michigan 48201, USA. jgranne@med.wayne.edu
Lahners
K N
KN
Zhai
Y
Y
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D008969:Molecular Sequence Data; D009154:Mutation; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000737:chemistry / Q000187:drug effects* / Q000235:genetics; D018342:Receptors, Adrenergic, beta-1 / Q000737:chemistry / Q000187:drug effects* / Q000235:genetics; D022702:Receptors, Adrenergic, beta-3; D011993:Recombinant Fusion Proteins / Q000187:drug effects*; D017386:Sequence Homology, Amino Acid
D000318:Adrenergic beta-Agonists; D011943:Receptors, Adrenergic, beta; D018342:Receptors, Adrenergic, beta-1; D022702:Receptors, Adrenergic, beta-3; D011993:Recombinant Fusion Proteins