Division of Neurobiology, Barrow Neurological Institute and St. Joseph's Hospital and Medical Center, Phoenix, Arizona 85013, USA.
J Biol Chem. 2011 Jul 15;286(28):25331-40. doi: 10.1074/jbc.M111.221754. Epub 2011 May 24.
Binding of a neurotransmitter to its membrane receptor opens an integral ion conducting pore. However, prolonged exposure to the neurotransmitter drives the receptor to a refractory state termed desensitization, which plays an important role in shaping synaptic transmission. Despite intensive research in the past, the structural mechanism of desensitization is still elusive. Using mutagenesis and voltage clamp in an oocyte expression system, we provide several lines of evidence supporting a novel hypothesis that uncoupling between binding and gating machinery is the underlying mechanism for α7 nicotinic receptor (nAChR) desensitization. First, the decrease in gate tightness was highly correlated to the reduced desensitization. Second, nonfunctional mutants in three important coupling loops (loop 2, loop 7, and the M2-M3 linker) could be rescued by a gating mutant. Furthermore, the decrease in coupling strength in these rescued coupling loop mutants reversed the gating effect on desensitization. Finally, coupling between M1 and hinge region of the M2-M3 linker also influenced the receptor desensitization. Thus, the uncoupling between N-terminal domain and transmembrane domain, governed by the balance of coupling strength and gate tightness, underlies the mechanism of desensitization for the α7 nAChR.
神经递质与其膜受体结合会打开一个完整的离子通道。然而，长时间暴露于神经递质会导致受体进入失敏状态，称为脱敏，这在塑造突触传递中起着重要作用。尽管过去进行了深入的研究，但脱敏的结构机制仍然难以捉摸。我们使用卵母细胞表达系统中的突变和电压钳技术，提供了几条证据支持一种新的假设，即结合和门控机制的解耦是 α7 烟碱型乙酰胆碱受体 (nAChR) 脱敏的潜在机制。首先，门控紧密度的降低与脱敏的减少高度相关。其次，三个重要的偶联环（环 2、环 7 和 M2-M3 接头）中的非功能突变体可以被门控突变体拯救。此外，这些挽救的偶联环突变体中偶联强度的降低逆转了门控对脱敏的影响。最后，M1 和 M2-M3 接头的铰链区之间的偶联也影响受体的脱敏。因此，由偶联强度和门控紧密度平衡控制的 N 端结构域和跨膜结构域之间的解耦是 α7 nAChR 脱敏的机制。
