Substrate binding accelerates the conformational transitions and substrate dissociation in multidrug efflux transporter AcrB.
Substrate binding accelerates the conformational transitions and substrate dissociation in multidrug efflux transporter AcrB.
复制标题
底物结合加速多药外排转运蛋白 AcrB 中的构象转变和底物解离
DOI：
10.3389/fmicb.2015.00302
复制
发表时间：
2015
影响因子：
5.2
通讯作者：
Wang W
中科院分区：
文献类型：
--
作者：
Wang B;Weng J;Wang W
三联外排泵AcrAB-TolC是大肠杆菌主要的多药耐药转运蛋白。杆菌内膜转运蛋白AcrB是一种同源三聚体，由质子沿跨膜电化学梯度向下运动提供能量。Acr B的不对称晶体结构具有三个处于不同构象状态[进入（A）、结合（B）和挤出（E）]的单体，支持功能旋转机制，其中Acr B的每个单体以协调的方式在三种状态之间循环。然而，功能旋转过程中的构象变化与药物转运之间的关系尚未完全清楚。在这里，我们探讨了构象变化的AcrB同源三聚体在ABE到ESTA过渡在不同的底物结合状态，使用有针对性的MD模拟。结果表明，底物从B单体远端结合口袋中解离与转运途径中的协同构象变化密切相关，特别是Phe 628和Tyr 327的侧链重定向。第二底物结合在A单体的近端结合口袋处，明显加速了B单体的构象转变和底物解离。多底物结合模式的加速效应为底物外排动力学研究中观察到的正协同性提供了分子解释，加深了我们对AcrB功能旋转机制的理解。
The tripartite efflux pump assembly AcrAB-TolC is the major multidrug resistance transporter in E. coli. The inner membrane transporter AcrB is a homotrimer, energized by the proton movement down the transmembrane electrochemical gradient. The asymmetric crystal structures of AcrB with three monomers in distinct conformational states [access (A), binding (B) and extrusion (E)] support a functional rotating mechanism, in which each monomer of AcrB cycles among the three states in a concerted way. However, the relationship between the conformational changes during functional rotation and drug translocation has not been totally understood. Here, we explored the conformational changes of the AcrB homotrimer during the ABE to BEA transition in different substrate-binding states using targeted MD simulations. It was found that the dissociation of substrate from the distal binding pocket of B monomer is closely related to the concerted conformational changes in the translocation pathway, especially the side chain reorientation of Phe628 and Tyr327. A second substrate binding at the proximal binding pocket of A monomer evidently accelerates the conformational transitions as well as substrate dissociation in B monomer. The acceleration effect of the multi-substrate binding mode provides a molecular explanation for the positive cooperativity observed in the kinetic studies of substrate efflux and deepens our understanding of the functional rotating mechanism of AcrB.