Mukhtasimova Nuriya, Sine Steven M
Department of Physiology and Biomedical Engineering, Receptor Biology Laboratory, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
J Neurosci. 2007 Apr 11;27(15):4110-9. doi: 10.1523/JNEUROSCI.0025-07.2007.
Binding of neurotransmitter triggers gating of synaptic receptor channels, but our understanding of the structures that link the binding site to the channel is just beginning to develop. Here, we identify an intersubunit triggering element required for rapid and efficient gating of muscle nicotinic receptors using a structural model of the Torpedo receptor at 4 A resolution, recordings of currents through single receptor channels, measurements of inter-residue energetic coupling, and functional consequences of disulfide trapping. Mutation of the conserved residues, alphaTyr 127, epsilonAsn 39, and deltaAsn 41, located at the two subunit interfaces that form the agonist binding sites, markedly attenuates acetylcholine-elicited channel gating; mutant cycle analyses based on changes in the channel gating equilibrium constant reveal strong energetic coupling among these residues. After each residue is substituted with Cys, oxidizing conditions that promote disulfide bond formation attenuate gating of mutant, but not wild-type receptors. Gating is similarly attenuated when the Cys substitutions are confined to either of the binding-site interfaces, but can be restored by reducing conditions that promote disulfide bond breakage. Thus, the Tyr-Asn pair is an intersubunit trigger of rapid and efficient gating of muscle nicotinic receptors.
神经递质的结合会触发突触受体通道的门控，但我们对将结合位点与通道相连的结构的理解才刚刚开始发展。在这里，我们使用分辨率为4埃的电鳐受体结构模型、通过单受体通道的电流记录、残基间能量耦合的测量以及二硫键捕获的功能后果，确定了肌肉烟碱型受体快速有效门控所需的亚基间触发元件。位于形成激动剂结合位点的两个亚基界面处的保守残基αTyr 127、εAsn 39和δAsn 41的突变，显著减弱了乙酰胆碱引发的通道门控；基于通道门控平衡常数变化的突变循环分析揭示了这些残基之间强烈的能量耦合。在用半胱氨酸取代每个残基后，促进二硫键形成的氧化条件会减弱突变体而非野生型受体的门控。当半胱氨酸取代仅限于任一结合位点界面时，门控同样会减弱，但可以通过促进二硫键断裂的还原条件恢复。因此，Tyr-Asn对是肌肉烟碱型受体快速有效门控的亚基间触发因素。
