Dept of Physiology, UT Southwestern Medical Center, Dallas, TX, 75390, USA.
Dept of Physiology, UT Southwestern Medical Center, Dallas, TX, 75390, USA; Laboratory of Molecular Neurodegeneration, St Petersburg State Polytechnical Universty, St Petersburg, 195251, Russian Federation.
Biochem Biophys Res Commun. 2023 Sep 3;671:18-25. doi: 10.1016/j.bbrc.2023.05.110. Epub 2023 Jun 7.
Parkinson Disease (PD) is a progressive neurodegenerative disorder that is caused by dysfunction and death of dopaminergic neurons. Mutations in the gene encoding α-synuclein (ASYN) have been linked with familial PD (FPD). Despite important role of ASYN in PD pathology, its normal biological function has not been clarified, although direct action of ASYN in synaptic transmission and dopamine (DA) release have been proposed. In the present report we propose a novel hypothesis that ASYN functions as DA/H exchanger that can facilitate transport of dopamine across synaptic vesicle (SV) membrane by taking advantage of proton gradient between SV lumen and cytoplasm. According to this hypothesis, normal physiological role of ASYN consists of fine-tuning levels of dopamine in the SVs based on cytosolic concentration of dopamine and intraluminal pH. This hypothesis is based on similarity in domain structure of ASYN and pHILP, a designed peptide developed to mediate loading of lipid nanoparticles with the cargo molecules. We reason that carboxy-terminal acidic loop D2b domain in both ASYN and pHILP binds cargo molecules. By mimicking DA association with E/D residues in D2b domain of ASYN using Tyrosine replacement approach (TR) we have been able to estimate that ASYN is able to transfer 8-12 molecules of dopamine across SV membrane on each DA/H exchange cycle. Our results suggest that familial PD mutations (A30P, E46K, H50Q, G51D, A53T and A53E) will interfere with different steps of the exchange cycle, resulting in partial loss of dopamine transport function phenotype. We also predict that similar impairment in ASYN DA/H exchange function also occurs as a result on neuronal aging due to changes in SV lipid composition and size and also dissipation of pH gradient across SV membrane. Proposed novel functional role of ASYN provides novel insights into its biological role and its role in PD pathogenesis.
帕金森病 (PD) 是一种进行性神经退行性疾病，由多巴胺能神经元的功能障碍和死亡引起。编码α-突触核蛋白 (ASYN) 的基因突变与家族性 PD (FPD) 有关。尽管 ASYN 在 PD 病理学中具有重要作用，但它的正常生物学功能仍不清楚，尽管已经提出了 ASYN 对突触传递和多巴胺 (DA) 释放的直接作用。在本报告中，我们提出了一个新的假设，即 ASYN 作为 DA/H 交换器发挥作用，可以利用 SV 腔和细胞质之间的质子梯度，促进多巴胺穿过 SV 膜的转运。根据这一假设，ASYN 的正常生理作用包括根据胞质内多巴胺浓度和腔内 pH 值，精细调节 SV 中多巴胺的水平。这一假设基于 ASYN 和 pHILP 的结构域相似性，pHILP 是一种设计的肽，用于介导 cargo 分子加载到脂质纳米颗粒中。我们认为，ASYN 和 pHILP 中的羧基末端酸性环 D2b 结构域结合 cargo 分子。通过使用酪氨酸替代方法 (TR) 模拟 DA 与 ASYN D2b 结构域中的 E/D 残基的结合，我们能够估计 ASYN 能够在每个 DA/H 交换循环中跨 SV 膜转运 8-12 个多巴胺分子。我们的结果表明，家族性 PD 突变 (A30P、E46K、H50Q、G51D、A53T 和 A53E) 将干扰交换循环的不同步骤，导致多巴胺转运功能部分丧失表型。我们还预测，由于 SV 脂质组成和大小的变化以及 SV 膜跨膜 pH 梯度的耗散，神经元老化也会导致 ASYN 的 DA/H 交换功能类似的损伤。ASYN 新的功能作用假设为其生物学作用及其在 PD 发病机制中的作用提供了新的见解。
