Chemical synaptic transmission represents the most sophisticated dynamic process and is highly regulated with optimized neurotransmitter balance. Imbalanced transmitters can lead to transmission impairments, for example, intracellular zinc accumulation is a hallmark of degenerating neurons. However, the underlying mechanisms remain elusive. Postsynaptic density protein-95 (PSD-95) is a primary postsynaptic membrane-associated protein and the major scaffolding component in the excitatory postsynaptic densities, which performs substantial functions in synaptic development and maturation. Its membrane association induced by palmitoylation contributes largely to its regulatory functions at postsynaptic sites. Unlike other structural domains in PSD-95, the N-terminal region (PSD-95NT) is flexible and interacts with various targets, which modulates its palmitoylation of two cysteines (C3/C5) and glutamate receptor distributions in postsynaptic densities. PSD-95NT contains a putative zinc-binding motif (C2H2) with undiscovered functions. This study is the first effort to investigate the interaction between Zn²⁺ and PSD-95NT. The NMR titration of ¹⁵N-labeled PSD-95NT by ZnCl₂ was performed and demonstrated Zn²⁺ binds to PSD-95NT with a binding affinity (K_d) in the micromolar range. The zinc binding was confirmed by fluorescence and mutagenesis assays, indicating two cysteines and two histidines (H24, H28) are critical residues for the binding. These results suggested the concentration-dependent zinc binding is likely to influence PSD-95 palmitoylation since the binding site overlaps the palmitoylation sites, which was verified by the mimic PSD-95 palmitoyl modification and intact cell palmitoylation assays. This study reveals zinc as a novel modulator for PSD-95 postsynaptic membrane association by chelating its N-terminal region, indicative of its importance in postsynaptic signaling.

中文翻译：

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锌螯合突触后密度-95 N-末端损害其棕榈酰修饰

化学突触传递代表了最复杂的动态过程，并通过优化的神经递质平衡进行高度调节。不平衡的发射器可导致传输障碍，例如，细胞内锌积累是退化神经元的标志。然而，潜在的机制仍然难以捉摸。突触后密度蛋白 95 (PSD-95) 是一种主要的突触后膜相关蛋白，是兴奋性突触后密度中的主要支架成分，在突触发育和成熟中发挥重要作用。其由棕榈酰化诱导的膜结合在很大程度上有助于其在突触后位点的调节功能。与 PSD-95 中的其他结构域不同，N 末端区域 (PSD-95NT) 是灵活的并与各种目标相互作用，它调节两个半胱氨酸 (C3/C5) 的棕榈酰化和突触后密度中的谷氨酸受体分布。PSD-95NT 包含一个假定的锌结合基序 (C2H2)，具有未发现的功能。本研究首次尝试研究 Zn 之间的相互作用²⁺和 PSD-95NT。_{用 ZnCl 2对}¹⁵ N-标记的 PSD-95NT 进行NMR 滴定，证明 Zn ²⁺与 PSD-95NT 具有结合亲和力（K _d) 在微摩尔范围内。锌结合通过荧光和诱变测定得到证实，表明两个半胱氨酸和两个组氨酸（H24、H28）是结合的关键残基。这些结果表明，浓度依赖性锌结合可能影响 PSD-95 棕榈酰化，因为结合位点与棕榈酰化位点重叠，这已通过模拟 PSD-95 棕榈酰化修饰和完整细胞棕榈酰化测定得到证实。这项研究通过螯合其 N 末端区域，揭示了锌作为 PSD-95 突触后膜结合的新型调节剂，表明它在突触后信号传导中的重要性。