Molecular mechanism for agonist-promoted alpha(2A)-adrenoceptor activation by norepinephrine and epinephrine.
We present a mechanism for agonist-promoted alpha(2A)-adrenergic receptor (alpha(2A)-AR) activation based on structural, pharmacological, and theoretical evidence of the interactions between phenethylamine ligands and alpha(2A)-AR. In this study, we have: 1) isolated enantiomerically pure phenethylamines that differ both in their chirality about the beta-carbon, and in the presence/absence of one or more hydroxyl groups: the beta-OH and the catecholic meta- and para-OH groups; 2) used [(3)H]UK-14,304 [5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine; agonist] and [(3)H]RX821002 [2-(2-methoxy-1,4-benzodioxan-2-yl)-2-imidazoline; antagonist] competition binding assays to determine binding affinities of these ligands to the high- and low-affinity forms of alpha(2A)-AR; 3) tested the ability of the ligands to promote receptor activation by measuring agonist-induced stimulation of [(35)S]GTPgammaS binding in isolated cell membranes; and 4) used automated docking methods and our alpha(2A)-AR model to predict the binding modes of the ligands inside the alpha(2A)-AR binding site. The ligand molecules are sequentially missing different functional groups, and we have correlated the structural features of the ligands and ligand-receptor interactions with experimental ligand binding and receptor activation data. Based on the analysis, we show that structural rearrangements in transmembrane helix (TM) 5 could take place upon binding and subsequent activation of alpha(2A)-AR by phenethylamine agonists. We suggest that the following residues are important in phenethylamine interactions with alpha(2A)-AR: Asp113 (D(3.32)), Val114 (V(3.33)), and Thr118 (T(3.37)) in TM3; Ser200 (S(5.42)), Cys201 (C(5.43)), and Ser204 (S(5.46)) in TM5; Phe391 (F(6.52)) and Tyr394 (Y(6.55)) in TM6; and Phe411 (F(7.38)) and Phe412 (F(7.39)) in TM7.
Nyrönen
T
T
Department of Biochemistry and Pharmacy, Abo Akademi University, Turku, Finland.
Pihlavisto
M
M
Peltonen
J M
JM
Hoffrén
A M
AM
Varis
M
M
Salminen
T
T
Wurster
S
S
Marjamäki
A
A
Kanerva
L
L
Katainen
E
E
Laaksonen
L
L
Savola
J M
JM
Scheinin
M
M
Johnson
M S
MS
D000322:Adrenergic Agonists / Q000494:pharmacology*; D000818:Animals; D001667:Binding, Competitive; D016466:CHO Cells; D002396:Catechols / Q000737:chemistry; D006224:Cricetinae; D004837:Epinephrine / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology*; D006841:Hydrocarbons, Aromatic / Q000737:chemistry; D008958:Models, Molecular; D009638:Norepinephrine / Q000737:chemistry / Q000494:pharmacology*; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014162:Transfection; D014316:Tritium
D000322:Adrenergic Agonists; D002396:Catechols; D006841:Hydrocarbons, Aromatic; D018341:Receptors, Adrenergic, alpha-2; D014316:Tritium; C034221:catechol; D009638:Norepinephrine; D004837:Epinephrine