Reassessment of the Unique Mode of Binding between Angiotensin II Type 1 Receptor and Their Blockers

<div><p>While the molecular structures of angiotensin II (Ang II) type 1 (AT₁) receptor blockers (ARBs) are very similar, they are also slightly different. Although each ARB has been shown to exhibit a unique mode of binding to AT₁ receptor, different positions of the AT₁ receptor have been analyzed and computational modeling has been performed using different crystal structures for the receptor as a template and different kinds of software. Therefore, we systematically analyzed the critical positions of the AT₁ receptor, Tyr¹¹³, Tyr¹⁸⁴, Lys¹⁹⁹, His²⁵⁶ and Gln²⁵⁷ using a mutagenesis study, and subsequently performed computational modeling of the binding of ARBs to AT₁ receptor using CXCR4 receptor as a new template and a single version of software. The interactions between Tyr¹¹³ in the AT₁ receptor and the hydroxyl group of olmesartan, between Lys¹⁹⁹ and carboxyl or tetrazole groups, and between His²⁵⁶ or Gln²⁵⁷ and the tetrazole group were studied. The common structure, a tetrazole group, of most ARBs similarly bind to Lys¹⁹⁹, His²⁵⁶ and Gln²⁵⁷ of AT₁ receptor. Lys¹⁹⁹ in the AT₁ receptor binds to the carboxyl group of EXP3174, candesartan and azilsartan, whereas oxygen in the amidecarbonyl group of valsartan may bind to Lys¹⁹⁹. The benzimidazole portion of telmisartan may bind to a lipophilic pocket that includes Tyr¹¹³. On the other hand, the n-butyl group of irbesartan may bind to Tyr¹¹³. In conclusion, we confirmed that the slightly different structures of ARBs may be critical for binding to AT₁ receptor and for the formation of unique modes of binding.</p> </div

Molecular modeling of the interactions between the 7 ARBs and the AT₁ receptor.

<p>Color notation in the helix is as follows: transmembrane (TM)1, orange; TM2, dark yellow; TM3, yellow; TM4, green; TM5, dark green; TM6, blue; and TM7, purple. </p

Possible molecular modeling of the interactions between a lipophilic pocket (gray zone) in the AT₁ receptor and telmisartan or irbesartan.

<p>Color notation in the helix is as follows: transmembrane (TM)3, yellow; TM5, dark green; and TM6, blue.</p

Molecular modeling of a close-up view of the interactions between the 7 ARBs and the AT₁ receptor.

<p>Color notation in the helix is as follows: transmembrane (TM)1, orange; TM3, yellow; TM5, dark green; TM6, blue; and TM7, purple.</p

Chemical structures of the angiotensin II type 1 receptor blockers EXP3174, which is an active metabolite of losartan, candesartan, valsartan, telmisartan, olmesartan, irbesartan and azilsartan.

<p>Chemical structures of the angiotensin II type 1 receptor blockers EXP3174, which is an active metabolite of losartan, candesartan, valsartan, telmisartan, olmesartan, irbesartan and azilsartan.</p

Binding affinities (<i>K</i>_d) of Ang II, olmesartan, R239470 and R794847 to AT₁ wild-type (WT) and mutant receptors.

<p>Binding affinities (<i>K</i>_d) of Ang II, olmesartan, R239470 and R794847 to AT₁ wild-type (WT) and mutant receptors.</p

Binding affinities (<i>K</i>_d) of Ang II and R compounds to AT₁ wild-type (WT) and mutant receptors.

<p>Binding affinities (<i>K</i>_d) of Ang II and R compounds to AT₁ wild-type (WT) and mutant receptors.</p

Binding affinities (<i>K</i>_d) of Ang II, olmesartan, R239470 and R794847 to AT₁ wild-type (WT) and mutant receptors.

<p>Binding affinities (<i>K</i>_d) of Ang II, olmesartan, R239470 and R794847 to AT₁ wild-type (WT) and mutant receptors.</p

Construction of olmesartan-related compounds.

<p>Construction of olmesartan-related compounds.</p

% inositol phosphate (IP) production with or without 1 µM of olmesartan and olmesartan-related compounds in COS1 cells transiently expressing the wild-type (WT) and N111G AT₁ receptor.

<p>The test compounds were added 1 h before the measurement of IP. 100% IP production indicates basal IP production in WT (1,033±149 cpm) and N111G (2,087±414 cpm) AT₁ receptor-transfected cells. Ang II (0.1 µM)-induced maximum IP production in WT and N111G AT₁ receptor-transfected cells were 4,037±479 cpm and 4,138±362 cpm, respectively. n=4–7, *p<0.05 vs. no treatment.</p