Structure of a pantothenate transporter and implications for ECF module sharing and energy coupling of group II ECF transporters
Structure of a pantothenate transporter and implications for ECF module sharing and energy coupling of group II ECF transporters
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泛酸转运蛋白的结构以及对 ECF 模块共享和 II 族 ECF 转运蛋白能量耦合的影响
DOI：
10.1073/pnas.1412246112
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发表时间：
2014-12-30
影响因子：
11.1
通讯作者：
Zhang, Peng
中科院分区：
文献类型：
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作者：
Zhang, Minhua;Bao, Zhihao;Zhang, Peng
意义通过确定泛酸能量偶联因子（ECF）转运蛋白LbECF-PanT的结构，我们揭示了一个EcfAA 'T模块如何与II组ECF转运蛋白中不同的S亚基相互作用的结构基础。我们还确定了介导分子间构象传递和/或影响转运蛋白复合物稳定性的残基，因此对转运蛋白活性至关重要。此外，我们确定了泛酸结合口袋和残基构成的口袋。最后但并非最不重要的是，我们发现，EcfT的结构是动态的，并在三个不同的转运蛋白复合物，赋予支架介导的复合物形成的ECF模块与各种EcfS蛋白发生了巨大的变化。这些研究结果被纳入一个更新的工作模型的ECF运输。能量偶联因子（ECF）转运蛋白是一类独特的ATP结合盒（ABC）转运蛋白，负责从环境中摄取微量营养素。每个ECF转运蛋白由S组分（或EcfS蛋白）和T/A/A′组分（或EcfT/A/A′蛋白; ECF模块）组成。在II组ECF转运蛋白中，几种EcfS蛋白共享一个ECF模块;然而，潜在的机制仍然未知。在这里，我们报告的结构的第二组ECF转运蛋白泛酸转运短乳杆菌（LbECF-PanT），其中共享的ECF模块与叶酸和羟甲基嘧啶转运蛋白（LbECF-FolT和LbECF-HmpT）。结构和突变分析揭示了构成泛酸结合口袋的残基。我们发现，虽然三个EcfS蛋白PanT，FolT和HmpT是不同的序列，他们共享一个共同的表面积组成的跨膜螺旋1/2/6（SM 1/2/6）与耦合螺旋2/3（CH 2/3）的相同的EcfT。CH 2主要通过疏水相互作用与SM 1相互作用，这可能调节EcfS的滑动运动。CH 3与SM 1、SM 2和SM 6形成的疏水表面沟结合，这可能将EcfA/A′的构象变化传递到EcfS。我们还发现，在LbECF-PanT的分子间表面的残基是必不可少的转运活性，这些残基可能介导分子间构象传递和/或影响转运复合物的稳定性。此外，我们发现，EcfT的结构是构象动态的，这支持其作为支架介导的ECF模块与各种EcfS蛋白的相互作用，形成不同的转运蛋白复合物的功能。
Significance By determining the structure of a pantothenate energy-coupling factor (ECF) transporter, LbECF-PanT, we revealed the structural basis of how one EcfAA'T module can interact with different S subunits among group II ECF transporters. We also identified the residues that mediate the intermolecular conformational transmission and/or affect the transporter complex stability, and thus are essential for transporter activity. In addition, we identified the pantothenate-binding pocket and the residues constituting the pocket. Last but not least, we found that the structure of EcfT is dynamic and undergoes dramatic changes in the three different transporter complexes, which confer scaffold-mediating complex formations of the ECF module with various EcfS proteins. These findings are incorporated into an updated working model of the ECF transporter. Energy-coupling factor (ECF) transporters are a unique group of ATP-binding cassette (ABC) transporters responsible for micronutrient uptake from the environment. Each ECF transporter is composed of an S component (or EcfS protein) and T/A/A′ components (or EcfT/A/A′ proteins; ECF module). Among the group II ECF transporters, several EcfS proteins share one ECF module; however, the underlying mechanism remains unknown. Here we report the structure of a group II ECF transporter–pantothenate transporter from Lactobacillus brevis (LbECF-PanT), which shares the ECF module with the folate and hydroxymethylpyrimidine transporters (LbECF-FolT and LbECF-HmpT). Structural and mutational analyses revealed the residues constituting the pantothenate-binding pocket. We found that although the three EcfS proteins PanT, FolT, and HmpT are dissimilar in sequence, they share a common surface area composed of the transmembrane helices 1/2/6 (SM1/2/6) to interact with the coupling helices 2/3 (CH2/3) of the same EcfT. CH2 interacts mainly with SM1 via hydrophobic interactions, which may modulate the sliding movement of EcfS. CH3 binds to a hydrophobic surface groove formed by SM1, SM2, and SM6, which may transmit the conformational changes from EcfA/A′ to EcfS. We also found that the residues at the intermolecular surfaces in LbECF-PanT are essential for transporter activity, and that these residues may mediate intermolecular conformational transmission and/or affect transporter complex stability. In addition, we found that the structure of EcfT is conformationally dynamic, which supports its function as a scaffold to mediate the interaction of the ECF module with various EcfS proteins to form different transporter complexes.