Variable stoichiometry of the TatA component of the twin-arginine protein transport system observed by in vivo single-molecule imaging
Variable stoichiometry of the TatA component of the twin-arginine protein transport system observed by in vivo single-molecule imaging
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DOI：
10.1073/pnas.0806338105
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发表时间：
2008-10-07
影响因子：
11.1
通讯作者：
Berks, Ben C.
中科院分区：
文献类型：
--
作者：
Leake, Mark C.;Greene, Nicholas P.;Berks, Ben C.
双精氨酸转运（达特）系统转运折叠蛋白穿过细菌细胞质膜和植物叶绿体的类囊体膜。达特途径的基本组分是膜蛋白TatA、TatB和TatC。TatA被认为形成达特系统的蛋白质易位元件。目前的达特运输模型预测寡聚状态的TatA和是否，以及如何，这种状态的变化在运输周期。我们通过对单个黄色荧光蛋白标记的TatA复合物进行生物物理分析，直接确定了TatA在活细胞中天然表达水平下的寡聚状态。TatA形成复合物，表现出广泛的化学计量，每个复合物平均约25个TatA亚基。傅立叶分析的化学计量分布表明，复合物组装从四聚体单元。模拟复合物的扩散行为表明，TatA原聚体作为一个环，而不是一束。每个细胞含有约15个移动的TatA复合物和约100个TatA分子的池，在膜中处于更分散的状态。驱动达特运输的质子动力的消散对TatA络合物的化学计量没有影响。TatA复合物在缺乏TatBC的细胞中不形成，表明TatBC控制TatA的寡聚状态。我们的数据支持达特运输机制的TatA聚合模型。
The twin-arginine translocation (Tat) system transports folded proteins across the bacterial cytoplasmic membrane and the thylakoid membrane of plant chloroplasts. The essential components of the Tat pathway are the membrane proteins TatA, TatB, and TatC. TatA is thought to form the protein translocating element of the Tat system. Current models for Tat transport make predictions about the oligomeric state of TatA and whether, and how, this state changes during the transport cycle. We determined the oligomeric state of TatA directly at native levels of expression in living cells by photophysical analysis of individual yellow fluorescent protein-labeled TatA complexes. TatA forms complexes exhibiting a broad range of stoichiometries with an average of approximate to 25 TatA subunits per complex. Fourier analysis of the stoichiometry distribution suggests the complexes are assembled from tetramer units. Modeling the diffusion behavior of the complexes suggests that TatA protomers associate as a ring and not a bundle. Each cell contains approximate to 15 mobile TatA complexes and a pool of approximate to 100 TatA molecules in a more disperse state in the membrane. Dissipation of the protonmotive force that drives Tat transport has no affect on TatA complex stoichiometry. TatA complexes do not form in cells lacking TatBC, suggesting that TatBC controls the oligomeric state of TatA. Our data support the TatA polymerization model for the mechanism of Tat transport.