Interplay between intracellular loop 1 and helix VIII of the angiotensin II type 2 receptor controls its activation
Interplay between intracellular loop 1 and helix VIII of the angiotensin II type 2 receptor controls its activation
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DOI：
10.1016/j.bcp.2019.07.018
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发表时间：
2019-10-01
影响因子：
5.8
通讯作者：
Leduc, Richard
中科院分区：
文献类型：
--
作者：
Connolly, Alexandre;Holleran, Brian J.;Leduc, Richard
血管紧张素II 2型受体（AT（2）R）是一种七螺旋受体，其信号传导机制尚未完全明确。在目前的贡献，我们着手确定参与AT（2）R激活的分子决定因素。虽然AT（2）R没有显示出参与G（q/11）、G（12）、G（i2）和β-抑制蛋白（β-arrestin，beta-arrestin）通路，但AT（1）R在血管紧张素II（AngII）刺激时也参与其中，螺旋VIII在最近发表的AT（2）R结构中的非典型定位可能在受体与下游效应物偶联的能力中发挥作用。在AT（2）R结构中，螺旋VIII向内指向胞内环3（ICL 3），与跨膜结构域6（TM 6）形成三级相互作用，可能阻碍信号传导效应物的进入。另一方面，在大多数A类GPCR中，发现螺旋VIII参与与ICL 1的三级相互作用并且远离效应物结合位点。在进一步研究AT（2）R结构后，我们发现胞内环1（ICL 1）内的残基可能参与驱动螺旋VIII的这种不寻常构象。为了探索这一假说，我们设计了一系列AT（1）R/AT（2）R受体嵌合体，以验证ICL 1和螺旋VIII在AT（2）R信号转导中的作用。将AT（1）R ICL 1替换为AT（2）R导致与G（i2）偶联的突变受体。AT（2）R的螺旋VIII和C-末端结构域被AT（1）R骨架取代，导致保留AT（1）R样信号传导特性的突变受体。这些结果表明，AT（2）R的C-末端部分与经典的GPCR信号传导相容，AT（2）R的ICL 1参与重新定位螺旋VIII，这阻碍了经典GPCR效应物如G蛋白或β arrs的参与。
The signaling mechanisms of the angiotensin II type 2 receptor (AT(2)R), a heptahelical receptor, have not yet been clearly and completely defined. In the present contribution, we set out to identify the molecular determinants involved in AT(2)R activation. Although AT(2)R has not been shown to engage G(q/11), G(12), G(i2), and beta-arrestin (beta arr) pathways as does the AT(1)R upon angiotensin II (AngII) stimulation, the atypical positioning of helix VIII in the recently published AT(2)R structure may play a role in the receptor's capacity to couple to downstream effectors. In the AT(2)R structure, helix VIII points inwards and towards intracellular loop 3 (ICL3) to form tertiary interactions with transmembrane domain 6 (TM6), possibly impeding access to signaling effectors. On the other hand, in most class A GPCRs, helix VIII is found to be engaged in tertiary interactions with ICL1 and away from the effector binding site. Upon closer examination of the AT(2)R structure, we found that the residues contained within intracellular loop 1 (ICL1) may be involved in driving this unusual conformation of helix VIII. To explore this hypothesis, we designed a series of AT(1)R/AT(2)R receptor chimeras to validate the roles of ICL1 and helix VIII in AT(2)R signaling. Substituting the AT(1)R ICL1 into AT(2)R led to a mutant receptor that coupled to G(i2). The substitution of the helix VIII and C-terminal domains of AT(2)R into the AT(1)R backbone led to a mutant receptor that retained AT(1)R-like signaling properties. These results suggest that the C-terminal portion of AT(2)R is compatible with canonical GPCR signaling and that ICL1 of AT(2)R is involved in repositioning helix VIII, which impedes engagement of classical GPCR effectors such as G proteins or beta arrs.