Mitochondrial and Plasma Membrane Citrate Transporters: Discovery of Selective Inhibitors and Application to Structure/Function Analysis.
Mitochondrial and Plasma Membrane Citrate Transporters: Discovery of Selective Inhibitors and Application to Structure/Function Analysis.
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发表时间：
2010-06
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通讯作者：
Jiakang Sun;Sreevidya Aluvila;R. Kotaria;J. Mayor;D. Walters;R. S. Kaplan
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作者：
Jiakang Sun;Sreevidya Aluvila;R. Kotaria;J. Mayor;D. Walters;R. S. Kaplan
胞质柠檬酸盐是脂肪酸、三酰甘油和胆固醇生物合成的主要碳源，并且还通过其对磷酸果糖激酶的别构抑制来调节葡萄糖代谢。其来源于内膜柠檬酸盐转运蛋白（CTP）上线粒体基质的柠檬酸盐流出或质膜柠檬酸盐转运蛋白（PMCT）上细胞外柠檬酸盐流入。尽管它们有共同的底物，但这两种转运蛋白几乎没有序列相似性，它们通过根本不同的机制转运柠檬酸盐。我们测试了一组先前鉴定的CTP抑制剂抑制PMCT的能力。我们发现，前10名CTP抑制剂中只有一个基本上抑制PMCT。相反，我们确定了另外两种抑制PMCT但对CTP影响不大的抑制剂。所有三个确定的PMCT抑制剂显示非竞争性机制。此外，模型来解释抑制剂与CTP的相互作用。作为本研究的一部分，基于亮氨酸转运蛋白的晶体结构开发了PMCT同源性模型，并确定了可能的柠檬酸盐结合位点，并将其组成与CTP中存在的两个已知柠檬酸盐结合位点进行了比较。选择性抑制PMCT的能力可能证明是药理学改善由过量脂质、胆固醇和葡萄糖合成引起的代谢紊乱（包括人肥胖症、高脂血症、高胆固醇血症和2型糖尿病）的关键。
Cytoplasmic citrate is the prime carbon source for fatty acid, triacylglycerol, and cholesterol biosyntheses, and also regulates glucose metabolism via its allosteric inhibition of phosphofructokinase. It originates either via the efflux of citrate from the mitochondrial matrix on the inner membrane citrate transport protein (CTP) or via the influx of extracellular citrate on the plasma membrane citrate transporter (PMCT). Despite their common substrate, the two transport proteins share little sequence similarity and they transport citrate via fundamentally different mechanisms. We tested the ability of a set of previously identified CTP inhibitors, to inhibit the PMCT. We found that of the top 10 CTP inhibitors only one substantially inhibited the PMCT. Conversely, we identified two other inhibitors that inhibited the PMCT but had little effect on the CTP. All three identified PMCT inhibitors displayed a noncompetitive mechanism. Furthermore, models to explain inhibitor interactions with the CTP are proposed. As part of the present studies a PMCT homology model has been developed based on the crystal structure of the leucine transporter, and a possible citrate binding site has been identified and its composition compared with the two known citrate binding sites present within the CTP. The ability to selectively inhibit the PMCT may prove key to the pharmacologic amelioration of metabolic disorders resulting from the synthesis of excess lipid, cholesterol, and glucose, including human obesity, hyperlipidemia, hyper-cholesterolemia, and Type 2 diabetes.