Rodent intestinal folate transporters (SLC46A1): secondary structure, functional properties, and response to dietary folate restriction
Rodent intestinal folate transporters (SLC46A1): secondary structure, functional properties, and response to dietary folate restriction
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DOI：
10.1152/ajpcell.00202.2007
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发表时间：
2007-11-01
影响因子：
5.5
通讯作者：
Goldman, I. David
中科院分区：
文献类型：
--
作者：
Qiu, Andong;Min, Sang Hee;Goldman, I. David
该实验室最近发现了一种编码肠道叶酸吸收所需的新型叶酸转运蛋白[智人质子偶联叶酸转运蛋白（HsPCFT）; SLC 46 A1]的人类基因。本研究主要针对小鼠（Mus musculus）PCFT（MmPCFT）和大鼠（Rattus norvegicus）PCFT（RnPCFT），并讨论了它们的二级结构、特异性、组织表达和膳食叶酸的调节。这两种啮齿动物PCFT蛋白质运输到细胞膜，其中仅在透化的HeLa细胞中，NH 2-和COOH-末端可接近靶向这些结构域的抗体。这与基于计算机的拓扑分析一起，与啮齿动物PCFT蛋白可能含有12个跨膜结构域的模型一致。[H-3]叶酸的转运在pH 5.5时最佳，并且由于Km的增加和V-max的降低而随着pH的增加而降低。在pH 7.0时，叶酸和甲氨蝶呤的流入可以忽略不计，但有残留的（6S）5甲基四氢叶酸转运。叶酸的摄取PCFT注射非洲爪蟾卵母细胞是产电和pH值依赖。电生理评估的MmPCFT和RnPCFT的叶酸内流Km值在pH 5.5时分别为0.7和0.3 μ M，在pH 6.5时分别为1.1和0.8 μ M。啮齿动物PCFT对单谷氨酰氨甲蝶呤具有高度特异性，但对多谷氨酰氨甲蝶呤没有特异性。MmPCFT mRNA在十二指肠、近端空肠、肝脏和肾脏中高度表达，在脑和其他组织中表达较少。MmPCFT蛋白定位于十二指肠和近端空肠的顶端刷状缘膜。在喂食叶酸缺乏的vesus叶酸充足饮食的小鼠中，近端小肠中的mmPCFT mRNA水平增加了13倍，这与PCFT在肠道叶酸吸收中发挥的关键作用一致。
This laboratory recently identified a human gene that encodes a novel folate transporter [Homo sapiens proton-coupled folate transporter (HsPCFT); SLC46A1] required for intestinal folate absorption. This study focused on mouse (Mus musculus) PCFT (MmPCFT) and rat (Rattus norvegicus) PCFT (RnPCFT) and addresses their secondary structure, specificity, tissue expression, and regulation by dietary folates. Both rodent PCFT proteins traffic to the cell membrane with the NH2- and COOH- termini accessible to antibodies targeted to these domains only in permeabilized HeLa cells. This, together with computer-based topological analyses, is consistent with a model in which rodent PCFT proteins likely contain 12 transmembrane domains. Transport of [H-3] folates was optimal at pH 5.5 and decreased with increasing pH due to an increase in K-m and a decrease in V-max. At pH 7.0, folic acid and methotrexate influx was negligible, but there was residual (6S) 5methyltetrahydrofolate transport. Uptake of folates in PCFT-injected Xenopus oocytes was electrogenic and pH dependent. Folic acid influx Km values of MmPCFT and RnPCFT, assessed electrophysiologically, were 0.7 and 0.3 mu M at pH 5.5 and 1.1 and 0.8 mu M at pH 6.5, respectively. Rodent PCFTs were highly specific for monoglutamyl but not polyglutamyl methotrexate. MmPCFT mRNA was highly expressed in the duodenum, proximal jejunum, liver, and kidney with lesser expression in the brain and other tissues. MmPCFT protein was localized to the apical brush-border membrane of the duodenum and proximal jejunum. MmPCFT mRNA levels increased similar to 13-fold in the proximal small intestine in mice fed a folate-deficient vesus folate-replete diet, consistent with the critical role that PCFT plays in intestinal folate absorption.