Mechanism of constitutive activation of the AT1 receptor:: Influence of the size of the agonist switch binding residue Asn111
Mechanism of constitutive activation of the AT1 receptor:: Influence of the size of the agonist switch binding residue Asn111
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DOI：
10.1021/bi980863t
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发表时间：
1998-11-10
期刊：
影响因子：
2.9
通讯作者：
Karnik, SS
中科院分区：
文献类型：
--
作者：
Feng, YH;Miura, SI;Karnik, SS
AT（1）受体是一种G蛋白偶联受体（GPCR）;其从基础状态（R）激活需要受体跨膜螺旋In（TM-III）中的Asn（111）与血管紧张素II（Ang II）的Tyr（4）残基之间的相互作用。Asn（111）至Gly（111）突变（N111 G）导致AT（1）受体的组成性激活（Noda等（1996）Biochemistry，35，16435-16442）。我们在这里表明，AT（1）受体TM-Ⅲ与AT（2）受体拓扑结构相同的16残基片段（Cys（101）-瓦尔（116））的替代诱导组成型活性，虽然Asn（111）在所得嵌合体CR 18中被保留。CR 18和N111 G突变的作用既不是累加的，也不是协同的。在任一突变体中诱导的构象模拟部分活化状态（R '），并且在两者中转变为完全活化的R* 构象不再需要Ang II的Tyr（4）。受体的R状态和Tyr（4）Ang II。通过在CR 18的111位引入较大尺寸的Phe侧链，可以恢复受体活化的依赖性，这表明CR 18突变产生了与N111 G突变中侧链尺寸减小相似的效果。与天然AT（1）受体相同，R'构象是由小于但不大于Asn（111）的残基取代产生的。然而，两种受体中几个其他TM-III残基的大小取代不影响R、R '和R* 状态之间的转换。因此，负责Asn（111）作为构象转换功能的性质既不是极性也不是氢键键合电位，而是侧链的大小。我们的结论是，AT（1）受体组成性激活的基本机制是增加关键激动剂-开关结合残基Asn（111）的熵。因此，通常激动剂依赖性R -> R'转变自发发生。该机制可以适用于许多其他GPCR。
The AT(1) receptor is a G-protein-coupled receptor (GPCR); its activation from the basal state (R) requires an interaction between Asn(111) in transmembrane helix In (TM-III) of the receptor and the Tyr(4) residue of angiotensin II (Ang II). Asn(111) to Gly(111) mutation (N111G) results in constitutive activation of the AT(1) receptor (Noda et al. (1996) Biochemistry, 35, 16435-16442). We show here that replacement of the AT(1) receptors TM-III with a topologically identical 16-residue segment (Cys(101)-Val(116)) from the AT(2) receptor induces constitutive activity, although Asn(111) is preserved in the resulting chimera, CR18. Effects of CR18 and N111G mutations are neither additive nor synergistic. The conformation(s) induced in either mutant mimics the partially activated state (R'), and transition to the fully activated R* conformation in both no longer requires the Tyr(4) of Ang II. Both the R state of the receptor and the Tyr(4) Ang II. dependence of receptor activation can be reinstated by introduction of a larger sized Phe side chain at the 111 position in CR18, suggesting that the CR18 mutation generated an effect similar to the reduction of side chain size in the N111G mutation. Consistently in the native AT(1) receptor, R' conformation is generated by replacement with residues smaller but not larger than the Asn(111). However, size substitution of several other TM-III residues in both receptors did not affect transitions between R, R', and R* states. Thus, the property responsible for Asn(111) function as a conformational switch is neither polarity nor hydrogen bonding potential but the side chain size. We conclude that the fundamental mechanism responsible for constitutive activation of the AT(1) receptor is to increase the entropy of the key agonist-switch binding residue, Asn(111). As a result, the normally agonist-dependent R --> R' transition occurs spontaneously. This mechanism may be applicable to many other GPCRs.