Molecular mechanism of citrate transporter NaCT and its mutations that cause pediatric epilepsies

总结 癫痫性脑病是一组异质性的严重癫痫发作疾病， 25%的儿童癫痫神经元柠檬酸转运蛋白SLC 13 A5/NaCT基因突变可使其功能丧失。 功能活动，引起早发性癫痫性脑病（EOEE）。病人在大脑中出现癫痫 生命的最初几个小时，并经历发育迟缓。Na+驱动的柠檬酸盐转运蛋白（NaCT）位于 神经元的质膜。作为柠檬酸循环的中间体，柠檬酸盐对能量至关重要 它在细胞中产生，并作为脂质和神经递质合成的前体。破坏 因此，可以理解的是，这种柠檬酸盐输入过程对神经元有害。根据它们的细胞表达 模式，导致EOEE的突变被分为两种类型。而I型（蛋白质位于 II型（位于质膜上的蛋白质）直接影响底物， 钠结合位点或阻断转运所必需的构象变化。基于同源性模型 从我们的细菌琥珀酸转运蛋白VcINDY的晶体结构构建的NaCT，我们假设每个 突变类型改变了NaCT结构并阻碍了转运活性。我们将描述这些机制 和结构变化的生物化学，生物物理和结构的方法相结合。结果 将有助于设计小分子增效剂和折叠校正剂， 患者

SUMMARY Epileptic encephalopathies are a heterogeneous group of severe seizure disorders accounting for approximately 25% of childhood epilepsies. Mutations in the neuronal citrate transporter SLC13A5/NaCT gene abolish its functional activity, causing early onset epileptic encephalopathy (EOEE). The patients display seizures in the first hours of life, and experience developmental delays. The Na+-driven citrate transporter (NaCT) is located in the plasma membrane of neurons. As an intermediate of the citric acid cycle, citrate is critical for energy production in the cell, and it acts as a precursor for the synthesis of lipids and neurotransmitters. Disruption of this citrate import process is therefore understandably harmful to neurons. According to their cellular expression patterns, mutations causing EOEE have been classified as two types. Whereas Type I (protein located in the ER) reduces protein stability, Type II (protein located in the plasma membrane) directly affects the substrate and sodium binding sites or blocks the conformational changes necessary for transport. Based on a homology model of NaCT built from our crystal structure of the bacterial succinate transporter VcINDY, we postulate how each type of mutation alters the NaCT structure and hinders transport activity. We will characterize the mechanisms and structural changes using a combination of biochemical, biophysical and structural approaches. The results will aid in the design of small molecule potentiators and folding correctors with the potential to help the young patients.