PT  - JOURNAL ARTICLE
AU  - Melissa T. Kelley
AU  - Tilmann Bürckstümmer
AU  - Katharina Wenzel-Seifert
AU  - Stefan Dove
AU  - Armin Buschauer
AU  - Roland Seifert
TI  - Distinct Interaction of Human and Guinea Pig Histamine  H<sub>2</sub>-Receptor with Guanidine-Type Agonists
AID  - 10.1124/mol.60.6.1210
DP  - 2001 Dec 01
TA  - Molecular Pharmacology
PG  - 1210--1225
VI  - 60
IP  - 6
4099  - http://molpharm.aspetjournals.org/content/60/6/1210.short
4100  - http://molpharm.aspetjournals.org/content/60/6/1210.full
SO  - Mol Pharmacol2001 Dec 01; 60
AB  - It is unknown why the potencies and efficacies of long-chained guanidine-type histamine H2-receptor (H2R) agonists are lower at the H2R of human neutrophils than at the H2R of the guinea pig atrium. To elucidate these differences, we analyzed fusion proteins of the human H2R (hH2R) and guinea pig H2R (gpH2R), respectively, and the short splice variant of Gsα(GsαS) expressed in Sf9 cells. The potencies and efficacies of small H2R agonists in the GTPase assay and the potencies of antagonists at inhibiting histamine-stimulated GTP hydrolysis by hH2R-GsαS and gpH2R-GsαS were similar. In contrast, the potencies and efficacies of guanidines were lower at hH2R-GsαS than at gpH2R-GsαS. Guanidines bound to hH2R-GsαS with lower affinity than to gpH2R-GsαS, and high-affinity binding of guanidines at gpH2R-GsαS was more resistant to disruption by GTPγS than binding at hH2R-GsαS. Molecular modeling suggested that the nonconserved Asp-271 in transmembrane domain 7 of gpH2R (Ala-271 in hH2R) confers high potency to guanidines. This hypothesis was confirmed by Ala-271→Asp-271 mutation in hH2R-GsαS. Intriguingly, the efficacies of guanidines at the Ala-271→Asp-271 mutant and at hH2R/gpH2R chimeras were lower than at gpH2R. Our model suggests that a Tyr-17/Asp-271 H-bond, present only in gpH2R-GsαS but not the other constructs studied, stabilizes the active guanidine-H2R state. Collectively, our data show 1) distinct interaction of H2R species isoforms with guanidines, 2) that a single amino acid in transmembrane domain 7 critically determines guanidine potency, and 3) that an interaction between transmembrane domains 1 and 7 is important for guanidine efficacy.