Apple Sucrose Transporter SUT1 and Sorbitol Transporter SOT6 Interact with Cytochrome b5 to Regulate Their Affinity for Substrate Sugars
Apple Sucrose Transporter SUT1 and Sorbitol Transporter SOT6 Interact with Cytochrome b5 to Regulate Their Affinity for Substrate Sugars
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苹果蔗糖转运蛋白 SUT1 和山梨醇转运蛋白 SOT6 与细胞色素 b5 相互作用，调节其对底物糖的亲和力
DOI：
10.1104/pp.109.141374
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发表时间：
2009-08-01
期刊：
影响因子：
7.4
通讯作者：
Zhang, Da-Peng
中科院分区：
文献类型：
--
作者：
Fan, Ren-Chun;Peng, Chang-Cao;Zhang, Da-Peng
糖转运蛋白是介导糖跨膜转运进入细胞的中心机制，糖的可利用性可以作为调节糖转运蛋白的信号。然而，在植物和动物细胞中，信号糖可用性调节糖转运的机制仍不清楚。在这里，我们报告，蔗糖转运蛋白，MdSUT 1，和山梨醇转运蛋白，MdSOT 6，都定位于质膜，被确定从苹果（苹果）果实。使用分裂泛素酵母双杂交，免疫沉淀和双分子荧光互补试验的组合，两个不同的糖转运蛋白被证明是相互作用的物理苹果内质网锚定细胞色素b5 MdCYB 5在体外和体内。在酵母系统中，这两种不同的相互作用复合物的功能是上调糖转运蛋白的亲和力，使细胞适应糖饥饿。MdCYB 5的拟南芥（Arabidopsis thaliana）同源物AtCYB 5-A也与两种糖转运蛋白相互作用，功能相似。MdSUT 1中的亮氨酸-73->脯氨酸和MdSOT 6中的亮氨酸-117->脯氨酸的点突变破坏了双分子相互作用，但没有显著影响转运蛋白活性，消除了糖转运蛋白-细胞色素b5复合物对糖转运蛋白亲和力的刺激作用。然而，酵母（酿酒酵母）细胞色素b5 ScCYB 5，一个额外的相互作用的合作伙伴的两种植物糖转运蛋白，没有功能的糖转运蛋白的调节，表明在酵母系统中观察到的生物功能是特定的植物细胞色素b5。这些发现提出了一种新的机制，植物细胞通过这种机制来调整糖的吸收以适应周围的糖可用性。
Sugar transporters are central machineries to mediate cross-membrane transport of sugars into the cells, and sugar availability may serve as a signal to regulate the sugar transporters. However, the mechanisms of sugar transport regulation by signal sugar availability remain unclear in plant and animal cells. Here, we report that a sucrose transporter, MdSUT1, and a sorbitol transporter, MdSOT6, both localized to plasma membrane, were identified from apple (Malus domestica) fruit. Using a combination of the split-ubiquitin yeast two-hybrid, immunocoprecipitation, and bimolecular fluorescence complementation assays, the two distinct sugar transporters were shown to interact physically with an apple endoplasmic reticulum-anchored cytochrome b5 MdCYB5 in vitro and in vivo. In the yeast systems, the two different interaction complexes function to upregulate the affinity of the sugar transporters, allowing cells to adapt to sugar starvation. An Arabidopsis (Arabidopsis thaliana) homolog of MdCYB5, AtCYB5-A, also interacts with the two sugar transporters and functions similarly. The point mutations leucine-73 -> proline in MdSUT1 and leucine-117 -> proline in MdSOT6, disrupting the bimolecular interactions but without significantly affecting the transporter activities, abolish the stimulating effects of the sugar transporter-cytochrome b5 complex on the affinity of the sugar transporters. However, the yeast (Saccharomyces cerevisiae) cytochrome b5 ScCYB5, an additional interacting partner of the two plant sugar transporters, has no function in the regulation of the sugar transporters, indicating that the observed biological functions in the yeast systems are specific to plant cytochrome b5s. These findings suggest a novel mechanism by which the plant cells tailor sugar uptake to the surrounding sugar availability.