Department of Biochemistry, University of Groningen, Nijenborgh 4, Groningen 9747, AG, The Netherlands.
Department of Biochemistry, University of Groningen, Nijenborgh 4, Groningen 9747, AG, The Netherlands.
J Mol Biol. 2018 Apr 13;430(8):1249-1262. doi: 10.1016/j.jmb.2018.02.014. Epub 2018 Feb 25.
GlnPQ is an ATP-binding cassette importer with a unique domain organization and intricate transport behavior. The protein has two extracytoplamic substrate-binding domains (SBDs) per membrane subunit, each with different specificity for amino acids and different spacing to the translocator domain. We determined the effect of the length and structure of the linkers, which connect the SBDs to each other and to the membrane-embedded translocator domain, on the transport by GlnPQ. We reveal that varying the linker length impacts transport in a dual manner that depends on the conformational dynamics of the SBD. Varying the linker length not only changes the time for the SBD to find the translocator (docking) but also changes the probability to release the substrate again, thus altering the transport efficiency. On the basis of the experimental data and mathematical modeling, we calculate the docking efficiency as function of linker length and lifetime of the closed conformation. Importantly, not only linker length but also features in the sequence are important for efficient delivery of substrate from SBD to the translocator. We show that the linkers provide a platform for SBD docking and are not merely flexible structures.
GlnPQ 是一种 ATP 结合盒转运蛋白，具有独特的结构域组织和复杂的转运行为。该蛋白每个膜亚基有两个细胞外基质结合域（SBD），每个 SBD 对氨基酸具有不同的特异性，与转运体域的间隔也不同。我们确定了连接 SBD 彼此以及与膜嵌入转运体域的接头的长度和结构对 GlnPQ 转运的影响。我们揭示了改变接头长度以依赖 SBD 的构象动力学的双重方式影响转运。改变接头长度不仅改变 SBD 找到转运体（对接）的时间，而且改变再次释放底物的概率，从而改变转运效率。基于实验数据和数学建模，我们计算了作为接头长度和封闭构象寿命函数的对接效率。重要的是，不仅接头长度，而且序列中的特征对于从 SBD 有效递送至转运体的底物也很重要。我们表明，接头为 SBD 对接提供了平台，而不仅仅是柔性结构。
