Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, UK.
Biochem J. 2010 Oct 15;431(2):217-25. doi: 10.1042/BJ20100890.
In mammalian cells, MCTs (monocarboxylate transporters) require association with an ancillary protein to enable plasma membrane expression of the active transporter. Basigin is the preferred binding partner for MCT1, MCT3 and MCT4, and embigin for MCT2. In rat and rabbit erythrocytes, MCT1 is associated with embigin and basigin respectively, but its sensitivity to inhibition by AR-C155858 was found to be identical. Using RT (reverse transcription)-PCR, we have shown that Xenopus laevis oocytes contain endogenous basigin, but not embigin. Co-expression of exogenous embigin was without effect on either the expression of MCT1 or its inhibition by AR-C155858. In contrast, expression of active MCT2 at the plasma membrane of oocytes was significantly enhanced by co-expression of exogenous embigin. This additional transport activity was insensitive to inhibition by AR-C155858 unlike that by MCT2 expressed with endogenous basigin that was potently inhibited by AR-C155858. Chimaeras and C-terminal truncations of MCT1 and MCT2 were also expressed in oocytes in the presence and absence of exogenous embigin. L-Lactate Km values for these constructs were determined and revealed that the TM (transmembrane) domains of an MCT, most probably TM7-TM12, but not the C-terminus, are the major determinants of L-lactate affinity, whereas the associated ancillary protein has little or no effect. Inhibitor titrations of lactate transport by these constructs indicated that embigin modulates MCT2 sensitivity to AR-C155858 through interactions with both the intracellular C-terminus and TMs 3 and 6 of MCT2. The C-terminus of MCT2 was found to be essential for its expression with endogenous basigin.
在哺乳动物细胞中，单羧酸转运蛋白（MCTs）需要与辅助蛋白结合才能使活性转运蛋白在质膜上表达。Basigin 是 MCT1、MCT3 和 MCT4 的首选结合伴侣，而 Embigin 是 MCT2 的结合伴侣。在大鼠和兔红细胞中，MCT1 分别与 Embigin 和 Basigin 相关，但发现其对 AR-C155858 的抑制敏感性相同。通过 RT-PCR，我们已经表明非洲爪蟾卵母细胞含有内源性 Basigin，但不含 Embigin。外源性 Embigin 的共表达对 MCT1 的表达或其对 AR-C155858 的抑制均无影响。相比之下，外源性活性 MCT2 在卵母细胞膜上的表达通过外源性 Embigin 的共表达显著增强。这种额外的转运活性对 AR-C155858 不敏感，与由内源性 Basigin 表达的 MCT2 不同，后者对 AR-C155858 的抑制作用很强。MCT1 和 MCT2 的嵌合体和 C 末端截短也在存在和不存在外源性 Embigin 的情况下在卵母细胞中表达。这些构建体的 L-乳酸 Km 值被确定，结果表明 MCT 的跨膜（TM）结构域，很可能是 TM7-TM12，但不是 C 末端，是 L-乳酸亲和力的主要决定因素，而相关的辅助蛋白几乎没有或没有影响。这些构建体的抑制剂滴定法表明，Embigin 通过与 MCT2 的细胞内 C 末端和 TM3 和 TM6 的相互作用调节 MCT2 对 AR-C155858 的敏感性。发现 MCT2 的 C 末端对于其与内源性 Basigin 的表达至关重要。
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