Majumder Puja, Mallela Aditya Kumar, Penmatsa Aravind
Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560012 India.
J Indian Inst Sci. 2018 Sep;98(3):283-300. doi: 10.1007/s41745-018-0081-5.
Cell membranes, despite providing a barrier to protect intracellular constituents, require selective gating for influx of important metabolites including ions, sugars, amino acids, neurotransmitters and efflux of toxins and metabolic end-products. The machinery involved in carrying out this gating process comprises of integral membrane proteins that use ionic electrochemical gradients or ATP hydrolysis, to drive concentrative uptake or efflux. The mechanism through which ion-coupled transporters function is referred to as alternating-access. In the recent past, discrete modes of alternating-access have been described with the elucidation of new transporter structures and their snapshots in altered conformational states. Despite X-ray structures being the primary sources of mechanistic information, other biophysical methods provide information related to the structural dynamics of these transporters. Methods including EPR and smFRET, have extensively helped validate or clarify ion-coupled transport mechanisms, in a near-native environment. This review seeks to highlight the mechanistic details of ion-coupled transport and delve into the biophysical tools and methods that help in understanding these fascinating molecules.
细胞膜尽管提供了一道屏障来保护细胞内成分，但对于包括离子、糖类、氨基酸、神经递质等重要代谢物的流入以及毒素和代谢终产物的流出，需要选择性门控。执行这种门控过程所涉及的机制包括整合膜蛋白，这些蛋白利用离子电化学梯度或ATP水解来驱动浓缩摄取或流出。离子偶联转运蛋白发挥作用的机制被称为交替式访问。最近，随着新的转运蛋白结构及其处于改变构象状态的快照的阐明，已经描述了交替式访问的不同模式。尽管X射线结构是机制信息的主要来源，但其他生物物理方法提供了与这些转运蛋白的结构动力学相关的信息。包括电子顺磁共振（EPR）和单分子荧光共振能量转移（smFRET）在内的方法，在近乎天然的环境中广泛地帮助验证或阐明了离子偶联转运机制。本综述旨在突出离子偶联转运的机制细节，并深入探讨有助于理解这些迷人分子的生物物理工具和方法。
