Structure-Function Basis of Attenuated Inverse Agonism of Angiotensin II Type 1 Receptor Blockers for Active-State Angiotensin II Type 1 Receptor

Abstract

Ligand-independent signaling by the angiotensin II type 1 receptor (AT1R) can be activated in clinical settings by mechanical stretch and autoantibodies as well as receptor mutations. Transition of the AT1R to the activated state is known to lower inverse agonistic efficacy of clinically used AT1R blockers (ARBs). The structure-function basis for reduced efficacy of inverse agonists is a fundamental aspect that has been understudied not only in relation to the AT1R but also regarding other homologous receptors. Here, we demonstrate that the active-state transition in the AT1R indeed attenuates an inverse agonistic effect of four biphenyl-tetrazole ARBs through changes in specific ligand-receptor interactions. In the ground state, tight interactions of four ARBs with a set of residues (Ser109 TM3 , Phe182 ECL2 , Gln257 TM6 , Tyr292 TM7 , and Asn295 TM7 ) results in potent inverse agonism. In the activated state, the ARB-AT1R interactions shift to a different set of residues (Val108 TM3 , Ser109 TM3 , Ala163 TM4 , Phe182 ECL2 , Lys199 TM5 , Tyr292 TM7 , and Asn295 TM7 ), resulting in attenuated inverse agonism. Interestingly, V108I, A163T, N295A, and F182A mutations in the activated state of the AT1R shift the functional response to the ARB binding toward agonism, but in the ground state the same mutations cause inverse agonism. Our data show that the second extracellular loop is an important regulator of the functional states of the AT1R. Our findings suggest that the quest for discovering novel ARBs, and improving current ARBs, fundamentally depends on the knowledge of the unique sets of residues that mediate inverse agonistic potency in the two states of the AT1R.

Current topics in angiotensin II type 1 receptor research: Focus on inverse agonism, receptor dimerization and biased agonism

“…We recently analyzed the structure-function relationships of losartan, EXP3174 (an active metabolite of losartan), valsartan and irbesartan for the basal and constitutively active states of AT1R, and identified the molecular mechanism of decreased maximal inverse agonist activity of the ARBs for the active state of AT1R compared to the ground state [16]. Details of the mechanism are described in Sections 3 through 5.…”

“…This landmark achievement paved the way for determination of the precise docking models of various ARBs based on the solved crystal structure [16, 43]. Energy-based docking simulations of the ARBs using the crystal structure of human AT1R revealed that the interactions of the biphenyl-tetrazole ARBs with AT1R were completely different from previously proposed ARB-AT1R interactions [16, 43, 44]. For example, differences of losartan binding mode between in a previously proposed AT1R model based on bovine rhodopsin structure and crystal structure of human AT1R are shown in Fig.…”

“…Although EXP3174 and candesartan bind in orientations similar to that of losartan, the carboxyl groups of EXP3174 and candesartan could form additional salt bridges with Arg167 ECL2 (Figs. 5B and C) [16, 43]. Moreover, the tetrazole group of candesartan is predicted to form a second salt bridge with Lys199 TM5 (Fig.…”

“…We recently identified the molecular mechanism associated with the decrease in inverse agonism [16]. Furthermore, studies revealed that AT1R can form both homodimers and AT1R-GPCR heterodimers, which can alter ligand binding and receptor function [17–25].…”

Molecular docking, 3D-QSAR and structural optimization on imidazo-pyridine derivatives dually targeting AT1 and PPARγ

“…Angiotensin receptor included in this system is a hypertension-related G protein-coupled receptor (GPCR) [21]. There are two main types: AT1 and angiotensin II type-2 receptor (AT2), among which the former receives the most research [22].…”