Thermodynamics-based mechanism for the regulation of substrate binding affinity of proton coupled drug transporters

底物与转运蛋白结合亲和力的调节是底物跨膜转运的关键因素之一。本研究采用等温滴定量热法（ITC）研究了质子偶联药物转运蛋白与底物的相互作用，并探讨了质子偶联底物转运的热力学机制。(1)在对EmrE作为反向转运蛋白的研究中发现，EmrE与TPP+的相互作用依赖于pH值，在较高的pH值下，EmrE与TPP+的亲和力增加，驱动力由熵驱动变为熵驱动，表明Glu 25可能是驱动底物结合的决定性残基之一。(2)在对YdgR作为共转运体的研究中发现，YdgR与Val-Ala相互作用的驱动力是熵变，而不依赖于pH。

Regulation of the binding affinity of the substrate into transporter is one of crucial factors to transport the substrate through the membrane. In this study, we had investigated the interaction between proton coupled drug transporters and these substrates by isothermal titration calorimetry (ITC) is a technique that can analyze the interaction energy with the substrate, and discussed the thermodynamics based mechanism of proton coupled substrate transport. (1) In the study of EmrE as antiporter, the interaction between EmrE and TPP+ depends on pH. At higher pH, the affinity increases, and the driving force becomes from enthalpy-driven to entropy-driven, and it is indicated that Glu25 might be one of determinant residues to drive the substrate binding. (2) In the study of YdgR as synporter, it was found that the driving force of interaction between YdgR and Val-Ala is entropy change, and it was not depend on pH.