Identification of a vesicular aspartate transporter
Identification of a vesicular aspartate transporter
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DOI：
10.1073/pnas.0804015105
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发表时间：
2008-08-19
影响因子：
11.1
通讯作者：
Moriyama, Yoshinori
中科院分区：
文献类型：
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作者：
Miyaji, Takaaki;Echigo, Noriko;Moriyama, Yoshinori
天冬氨酸是一种兴奋性氨基酸，在海马神经元的突触小泡和松果体细胞的突触样微泡 (SLMV) 中与谷氨酸共同储存，并通过与特定细胞受体结合而被胞吐并刺激邻近细胞。尽管越来越多的证据支持天冬氨酸神经传递的发生，但这一过程仍然存在争议，因为天冬氨酸的囊泡储存机制尚不清楚。在这里，我们发现唾液酸蛋白（一种溶酶体 H+/唾液酸协同转运蛋白）存在于海马突触小泡和松果体 SLMV 中。 RNA 干扰唾液酸蛋白表达可减少松果体细胞中天冬氨酸和谷氨酸的胞吐作用。当施加内部正膜电位作为驱动力时，含有纯化唾液酸蛋白的蛋白脂质体以相似的程度积极积累天冬氨酸和谷氨酸。在 Salla 病 (R39C) 患者中发现的携带突变的唾液酸蛋白完全缺乏天冬氨酸和谷氨酸转运活性，尽管它保留了明显的 H+/唾液酸共转运活性。这些结果强烈表明唾液酸蛋白具有双重生理功能并充当囊泡天冬氨酸/谷氨酸转运蛋白。萨拉病患者可能会失去天冬氨酸能（以及相关的谷氨酸能）神经传递，这可以解释为什么萨拉病会导致严重的神经缺陷。
Aspartate is an excitatory amino acid that is costored with glutamate in synaptic vesicles of hippocampal neurons and synaptic-like microvesicles (SLMVs) of pinealocytes and is exocytosed and stimulates neighboring cells by binding to specific cell receptors. Although evidence increasingly supports the occurrence of aspartergic neurotransmission, this process is still debated because the mechanism for the vesicular storage of aspartate is unknown. Here, we show that sialin, a lysosomal H+/sialic acid cotransporter, is present in hippocampal synaptic vesicles and pineal SLMVs. RNA interference of sialin expression decreased exocytosis of aspartate and glutamate in pinealocytes. Proteoliposomes containing purified sialin actively accumulated aspartate and glutamate to a similar extent when inside positive membrane potential is imposed as the driving force. Sialin carrying a mutation found in people suffering from Salla disease (R39C) was completely devoid of aspartate and glutamate transport activity, although it retained appreciable H+/sialic acid cotransport activity. These results strongly suggest that sialin possesses dual physiological functions and acts as a vesicular aspartate/glutamate transporter. It is possible that people with Salla disease lose aspartergic (and also the associated glutamatergic) neurotransmission, and this could provide an explanation for why Salla disease causes severe neurological defects.