Hsu Wei-Lin, Furuta Tadaomi, Sakurai Minoru
Center for Biological Resources and Informatics, Tokyo Institute of Technology, Midori-ku, Yokohama, Japan.
Proteins. 2018 Feb;86(2):237-247. doi: 10.1002/prot.25433. Epub 2017 Dec 11.
The Escherichia coli maltose transporter MalFGK -E belongs to the protein superfamily of ATP-binding cassette (ABC) transporters. This protein is composed of heterodimeric transmembrane domains (TMDs) MalF and MalG, and the homodimeric nucleotide-binding domains (NBDs) MalK . In addition to the TMDs and NBDs, the periplasmic maltose binding protein MalE captures maltose and shuttle it to the transporter. In this study, we performed all-atom molecular dynamics (MD) simulations on the maltose transporter and found that both the binding of MalE to the periplasmic side of the TMDs and binding of ATP to the MalK are necessary to facilitate the conformational change from the inward-facing state to the occluded state, in which MalK is completely dimerized. MalE binding suppressed the fluctuation of the TMDs and MalF periplasmic region (MalF-P2), and thus prevented the incorrect arrangement of the MalF C-terminal (TM8) helix. Without MalE binding, the MalF TM8 helix showed a tendency to intrude into the substrate translocation pathway, hindering the closure of the MalK . This observation is consistent with previous mutagenesis experimental results on MalF and provides a new point of view regarding the understanding of the substrate translocation mechanism of the maltose transporter.
大肠杆菌麦芽糖转运蛋白MalFGK -E属于ATP结合盒（ABC）转运蛋白的蛋白质超家族。该蛋白由异源二聚体跨膜结构域（TMDs）MalF和MalG以及同源二聚体核苷酸结合结构域（NBDs）MalK组成。除了TMDs和NBDs外，周质麦芽糖结合蛋白MalE捕获麦芽糖并将其转运至转运蛋白。在本研究中，我们对麦芽糖转运蛋白进行了全原子分子动力学（MD）模拟，发现MalE与TMDs周质侧的结合以及ATP与MalK的结合对于促进从内向状态到封闭状态的构象变化都是必要的，在封闭状态下MalK完全二聚化。MalE的结合抑制了TMDs和MalF周质区域（MalF-P2）的波动，从而防止了MalF C末端（TM8）螺旋的错误排列。没有MalE的结合，MalF TM8螺旋有侵入底物转运途径的趋势，阻碍了MalK的封闭。这一观察结果与先前关于MalF的诱变实验结果一致，并为理解麦芽糖转运蛋白的底物转运机制提供了新的视角。
