Synaptic Organizers: Dynamic Regulation of Trans-synaptic Bridges

突触组织者α-Neurexins与它们的突触后伙伴形成大分子桥梁， 跨越突触间隙(跨突触桥梁)；它们共同在调节突触方面发挥关键作用 神经元之间的连接和通信。α-Neurexins及其合作伙伴被卷入 神经障碍包括自闭症谱系障碍、精神分裂症和精神发育迟滞。 α-Neuresin跨突触桥传统上被认为是静态的。然而，还有 越来越多的证据表明，它们实际上是动态监管的！α-Neuresin反式调节的动态调节 突触桥是重要的，因为这意味着α-Neurexins的突触促进作用是可调节的，并且 可以在特定的突触上增加或减少。最近有三种非常不同的机制 揭示了控制α-Neurexins及其合作伙伴之间的跨突触桥梁：1)竞争诱饵， 2)星形胶质细胞分泌的蛋白质；3)α-Neuresin结合伙伴的变构调节。然而，它是 在分子水平上还不知道这些机制是如何工作的。分子碱基的测定是必不可少的。 这是这些调控机制的基础，因为它们不仅控制着突触促进活动 α-Neurexins，但它们也涉及可能被靶向操纵特定突触的蛋白质相互作用 连接性和治疗性利用。 在这项建议中，我们将确定三种机制的分子基础，这些机制控制着 α-Neuresin跨突触桥。我们假设这些不同的分子机制利用独特的 α3D结构中的元素-Neurexins及其合作伙伴生成允许动态 监管。我们将使用结构、生物物理和生化技术来阐明 1)相互竞争的突触组织者，2)星形细胞因子，3)变构调节。总而言之，我们的结果 将在分子水平上揭示调控机制如何塑造α-neuresin跨突触桥来影响 突触发育与突触交流。这一建议意义重大，因为 α-Neurexins及其合作伙伴参与了严重神经疾病的发病机制 调节它们的相互作用和功能，也控制它们对疾病的贡献。这项工作还将设置 开发以机制为基础的、专注于治疗特定中枢神经系统疾病的阶段。这 提案在概念上是创新的，因为它将有助于建立正在出现的范式转变，即跨 由突触组织者形成的突触桥梁，如α-Neurexins及其合作伙伴，实际上受到 强烈的调节及其稳定突触功能的能力可以通过其他相互作用来调节 蛋白质。这项提议在技术上也是创新的，因为它涉及单粒子电子断层扫描 为此，我们正在积极开发方法来对突触组织分子进行成像。

The synaptic organizers, α-neurexins, form macromolecular bridges with their post-synaptic partners that span the synaptic cleft (‘trans-synaptic bridges’); together they play a crucial role in mediating synaptic connections and communication between neurons. α-Neurexins and their partners are implicated in neurological disorders including autism spectrum disorder, schizophrenia and mental retardation. α-Neurexin trans-synaptic bridges have traditionally been considered static. However, there is accumulating evidence that they are in fact dynamically regulated! Dynamic regulation of α-neurexin trans- synaptic bridges is important, because it means that the synapse-promoting role of α-neurexins is tunable and can be increased or decreased at a particular synapse. Three very different mechanisms have recently been revealed that control the trans-synaptic bridges between α-neurexins and their partners: 1) competing decoys, 2) proteins secreted by astrocytes, and 3) allosteric modulation of α-neurexin binding partners. However, it is not known on a molecular level how these mechanisms work. It is essential to determine the molecular bases that underlie these regulatory mechanisms, because they not only control the synapse-promoting activity of α-neurexins, but they also involve protein interactions that could be targeted to manipulate specific synaptic connectivities and exploited therapeutically. In this proposal, we will determine the molecular bases of three mechanisms that control the formation of α-neurexin trans-synaptic bridges. We hypothesize that these different molecular mechanisms exploit unique elements in the 3D structure of α-neurexins and their partners to generate platforms that permit dynamic regulation. We will use structural, biophysical and biochemical techniques to elucidate mechanisms involving 1) competing synaptic organizers, 2) astrocytic factors, and 3) allosteric modulation. Collectively, our results will reveal on a molecular level how regulatory mechanisms mold α-neurexin trans-synaptic bridges impacting synapse development and synaptic communication. This proposal is significant because genetic lesions in α-neurexins and their partners are involved in the pathogenesis of severe neurological disorders, so mechanisms regulating their interactions and functions, control their contribution to disease as well. This work will also set the stage for developing mechanism-based, focused therapies to address specific CNS disorders. This proposal is conceptually innovative because it will help establish the emerging paradigm shift that trans- synaptic bridges formed by synaptic organizers, like α-neurexins and their partners, are in fact subject to intense regulation and their ability to stabilize synaptic function is rendered tunable by other interacting proteins. This proposal is also technically innovative because it involves single particle electron tomography for which we are actively developing methodologies to image synapse organizing molecules.