Ser165 of transmembrane helix IV is not involved in the interaction of catecholamines with the alpha-2a-adrenoceptor.
Molecular modeling studies have predicted that the beta-hydroxyl group of the catecholamines interacts with the beta 2-adrenoceptor at the serine residue at position 165 (Ser165) located on transmembrane helix IV; however, this has not been confirmed by site-directed mutagenesis. It has been inferred that this site, which is conserved in all of the nine known alpha- and beta-adrenoceptor subtypes, is also involved in the interaction of catecholamines with the alpha 2a-adrenoceptor. To test the hypothesis that the beta-hydroxyl group of the catecholamines interacts with Ser165 of the alpha 2a-adrenoceptor, we prepared a mutant alpha 2a-adrenoceptor where Ser165 was mutated to alanine. Mutation of Ser165 of the alpha 2a-adrenoceptor to alanine had no effect on the affinity of dopamine (which lacks the beta-hydroxyl group) or either enantiomer of norepinephrine or epinephrine (both of which possess the beta-hydroxyl group), indicating that Ser165 is not involved in the interaction of the catecholamines with the alpha 2a-adrenoceptor. We have previously shown that mutation of Ser90, located in transmembrane helix II, to either alanine or cysteine produces a selective reduction in the affinity of the (-)-enantiomers of the catecholamines for the alpha 2a-adrenoceptor, with no effect on the (+)-enantiomers or the corresponding beta-desoxy analogs. This is consistent with the known stereoselectivity involved in the interactions of catecholamines with the alpha 2a-adrenoceptor. The results of the present investigation indicate that Ser165 is not involved in the interaction of catecholamines with the alpha 2a-adrenoceptor. Because all known alpha-adrenoceptor subtypes have a serine residue at a position corresponding to Ser90 of the alpha 2a-adrenoceptor, it would appear that this site represents an important point for attachment of the beta-hydroxyl group of catecholamines.
Hehr
A
A
Department of Pharmacological Sciences, SmithKline Beecham Pharmaceuticals, King of Prussia, PA 19406-0939, USA.
Hieble
J P
JP
Li
Y O
YO
Bergsma
D J
DJ
Swift
A M
AM
Ganguly
S
S
Ruffolo
R R
RR
D000409:Alanine / Q000737:chemistry; D000818:Animals; D019556:COS Cells; D002395:Catecholamines / Q000737:chemistry / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism; D004837:Epinephrine / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009638:Norepinephrine / Q000378:metabolism; D011869:Radioligand Assay; D018341:Receptors, Adrenergic, alpha-2 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012694:Serine / Q000737:chemistry* / Q000235:genetics
D002395:Catecholamines; D018341:Receptors, Adrenergic, alpha-2; D012694:Serine; D000409:Alanine; D004298:Dopamine; D009638:Norepinephrine; D004837:Epinephrine