Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, 69978 Tel Aviv, Israel.
J Neurosci. 2011 Aug 31;31(35):12523-32. doi: 10.1523/JNEUROSCI.1527-11.2011.
Presynaptic inhibition via G-protein-coupled receptors (GPCRs) and voltage-gated Ca(2+) channels constitutes a widespread regulatory mechanism of synaptic strength. Yet, the mechanism of intermolecular coupling underlying GPCR-mediated signaling at central synapses remains unresolved. Using FRET spectroscopy, we provide evidence for formation of spatially restricted (<100 Å) complexes between GABA(B) receptors composed of GB(1a)/GB(2) subunits, Gα(o)β(1)γ(2) G-protein heterotrimer, and Ca(V)2.2 channels in hippocampal boutons. GABA release was not required for the assembly but for structural reorganization of the precoupled complex. Unexpectedly, GB(1a) deletion disrupted intermolecular associations within the complex. The GB(1a) proximal C-terminal domain was essential for association of the receptor, Ca(V)2.2 and Gβγ, but was dispensable for agonist-induced receptor activation and cAMP inhibition. Functionally, boutons lacking this complex-formation domain displayed impaired presynaptic inhibition of Ca(2+) transients and synaptic vesicle release. Thus, compartmentalization of the GABA(B1a) receptor, Gβγ, and Ca(V)2.2 channel in a signaling complex is required for presynaptic inhibition at hippocampal synapses.
通过 G 蛋白偶联受体 (GPCR) 和电压门控 Ca(2+) 通道的突触前抑制构成了突触强度的广泛调节机制。然而，中枢突触中 GPCR 介导的信号转导的分子间偶联机制仍未解决。使用荧光共振能量转移 (FRET) 光谱学，我们提供了证据表明 GABA(B) 受体由 GB(1a)/GB(2) 亚基、Gα(o)β(1)γ(2) G 蛋白异三聚体和 Ca(V)2.2 通道组成，在海马体末梢形成了空间受限 (<100 Å) 的复合物。GABA 释放对于组装但对于预偶联复合物的结构重排是必需的。出乎意料的是，GB(1a) 缺失破坏了复合物内的分子间相互作用。GB(1a) 近端 C 末端结构域对于受体、Ca(V)2.2 和 Gβγ 的关联是必需的，但对于激动剂诱导的受体激活和 cAMP 抑制是可有可无的。功能上，缺乏这种复合物形成域的末梢显示出 Ca(2+) 瞬变和突触囊泡释放的突触前抑制受损。因此，GABA(B1a) 受体、Gβγ 和 Ca(V)2.2 通道在信号复合物中的区室化是海马突触前抑制所必需的。
