Relative Rates of Amino Acid Import via the ABC Transporter GlnPQ Determine the Growth Performance of Lactococcus lactis
Relative Rates of Amino Acid Import via the ABC Transporter GlnPQ Determine the Growth Performance of Lactococcus lactis
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DOI：
10.1128/jb.00685-15
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发表时间：
2016-02-01
影响因子：
3.2
通讯作者：
Poolman, Bert
中科院分区：
文献类型：
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作者：
Fulyani, Faizah;Schuurman-Wolters, Gea K.;Poolman, Bert
乳酸乳球菌的GlnPQ转运蛋白具有一个显著特征，即有两个底物结合结构域（SBD）融合在跨膜结构域（TMD）的N末端，因此在同源二聚体复合物中存在四个SBD。尽管两个SBD都有X射线结构和配体结合数据，但对于不同氨基酸如何通过GlnPQ相互竞争转运却知之甚少。在此我们表明，GlnPQ具有比之前所认为的更广泛的底物特异性，它能够摄取天冬酰胺、谷氨酰胺和谷氨酸，尽管是通过不同途径且具有不同亲和力。天冬酰胺和谷氨酰胺在与SBD1和SBD2结合的层面上相互竞争（解离常数存在差异），但同时SBD1和SBD2在与转运结构域相互作用的层面上也相互竞争（亲和常数和转运速率存在差异）。尽管通过SBD1的谷氨酰胺转运会被生理浓度的天冬酰胺所抑制，但SBD2确保了必需氨基酸谷氨酰胺的高摄取速率。总之，这项研究表明，即使在存在竞争性天冬酰胺浓度的情况下，GlnPQ也具有转运谷氨酰胺的高能力，这与细胞对谷氨酰胺和谷氨酸的高需求相匹配。
重要性
GlnPQ是一种用于谷氨酰胺、谷氨酸和天冬酰胺的ATP结合盒（ABC）转运蛋白。该系统在各种革兰氏阳性细菌中是必不可少的，包括乳酸乳球菌和几种病原体。在此我们展示了氨基酸如何相互竞争与GlnPQ的多个SBD结合，以及这些SBD如何相互竞争将底物传递给转运蛋白。总体而言，我们的结果表明，GlnPQ已经进化到能够通过不同途径转运多种底物，并能最佳地获取丰富且必需的氨基酸谷氨酰胺。
The GlnPQ transporter from Lactococcus lactis has the remarkable feature of having two substrate-binding domains (SBDs) fused to the N terminus of the transmembrane domain (TMD), and thus four SBDs are present in the homodimeric complex. Although X-ray structures and ligand binding data are available for both SBDs, little is known of how different amino acids compete with each other for transport via GlnPQ. Here we show GlnPQ has a broader substrate specificity than previously thought, with the ability to take up asparagine, glutamine, and glutamic acid, albeit via different routes and with different affinities. Asparagine and glutamine compete with each other at the level of binding to SBD1 and SBD2 (with differences in dissociation constant), but at the same time SBD1 and SBD2 compete with each other at the level of interaction with the translocator domain (with differences in affinity constant and rate of transport). Although glutamine transport via SBD1 is outcompeted by physiological concentrations of asparagine, SBD2 ensures high rates of import of the essential amino acid glutamine. Taken together, this study demonstrates that even in the presence of competing asparagine concentrations, GlnPQ has a high capacity to transport glutamine, which matches the high needs of the cell for glutamine and glutamate.IMPORTANCEGlnPQ is an ATP-binding cassette (ABC) transporter for glutamine, glutamic acid, and asparagine. The system is essential in various Gram-positive bacteria, including L. lactis and several pathogens. Here we show how the amino acids compete with each other for binding to the multiple SBDs of GlnPQ and how these SBDs compete with each other for substrate delivery to the transporter. Overall, our results show that GlnPQ has evolved to transport diverse substrates via different paths and to optimally acquire the abundant and essential amino acid glutamine.