Serotonin transporter-ibogaine complexes illuminate mechanisms of inhibition and transport
Serotonin transporter-ibogaine complexes illuminate mechanisms of inhibition and transport
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DOI：
10.1038/s41586-019-1135-1
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发表时间：
2019-05-02
期刊：
影响因子：
64.8
通讯作者：
Gouaux, Eric
中科院分区：
文献类型：
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作者：
Coleman, Jonathan A.;Yang, Dongxue;Gouaux, Eric
5-羟色胺转运蛋白（SERT）通过5-羟色胺进入突触前神经元的钠和氯依赖性再循环来调节神经递质稳态（1-3）。使用选择性5-羟色胺再摄取通道（竞争性阻断底物结合从而延长神经递质作用的小分子）治疗重度抑郁症和焦虑症（2，4）。多巴胺和去甲肾上腺素转运体与SERT一起是神经递质钠同向转运体（NSS）家族的成员。NSS的转运活动可被可卡因和安非他明抑制或调节（2，3），NSS的遗传变异与几种神经精神障碍相关，包括注意缺陷多动障碍、自闭症和双相情感障碍（2，5）。对细菌NSS同源物（包括LeuT）的研究表明，它们的跨膜螺旋（TM）在转运周期中如何发生构象变化，使膜两侧的中心结合位点暴露（1，6 -12）。然而，与运输NSS的构象变化仍然未知。为了阐明SERT中基于结构的转运机制，我们研究了其与伊波替尼的复合物，伊波替尼是一种具有精神活性和抗成瘾特性的致幻天然产物（13，14）。值得注意的是，伊波替尼是一种非竞争性转运抑制剂，但对选择性5-羟色胺再摄取抑制剂表现出竞争性结合（15，16）。在这里，我们报告低温电子显微镜结构的SERT-ibocyanate复合物捕获在向外开放，闭塞和向内开放的构象。伊波替尼与中心结合位点结合，细胞外闸门的关闭主要涉及TM 1b和6a的运动。细胞内闸门的打开涉及TM 1a的铰链样运动和TM 5的部分解旋，它们一起创建了使底物和离子扩散到细胞质的渗透途径。这些结构定义了从向外开放到向内开放构象发生的结构重排，并提供了对神经递质转运和iboclavin抑制机制的深入了解。
The serotonin transporter (SERT) regulates neurotransmitter homeostasis through the sodium- and chloride-dependent recycling of serotonin into presynaptic neurons(1-3). Major depression and anxiety disorders are treated using selective serotonin reuptake inhibitors-small molecules that competitively block substrate binding and thereby prolong neurotransmitter action(2,4). The dopamine and noradrenaline transporters, together with SERT, are members of the neurotransmitter sodium symporter (NSS) family. The transport activities of NSSs can be inhibited or modulated by cocaine and amphetamines(2,3), and genetic variants of NSSs are associated with several neuropsychiatric disorders including attention deficit hyperactivity disorder, autism and bipolar disorder(2,5). Studies of bacterial NSS homologues-including LeuT-have shown how their transmembrane helices (TMs) undergo conformational changes during the transport cycle, exposing a central binding site to either side of the membrane(1,6-12). However, the conformational changes associated with transport in NSSs remain unknown. To elucidate structure-based mechanisms for transport in SERT we investigated its complexes with ibogaine, a hallucinogenic natural product with psychoactive and anti-addictive properties(13,14.) Notably, ibogaine is a non-competitive inhibitor of transport but displays competitive binding towards selective serotonin reuptake inhibitors(15,16). Here we report cryo-electron microscopy structures of SERT-ibogaine complexes captured in outward-open, occluded and inward-open conformations. Ibogaine binds to the central binding site, and closure of the extracellular gate largely involves movements of TMs 1b and 6a. Opening of the intracellular gate involves a hinge-like movement of TM1a and the partial unwinding of TM5, which together create a permeation pathway that enables substrate and ion diffusion to the cytoplasm. These structures define the structural rearrangements that occur from the outward-open to inward-open conformations, and provide insight into the mechanism of neurotransmitter transport and ibogaine inhibition.