ION TRANSPORTER

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目及 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 在这个实验中，我们的目的是确定的Na+/K+同向转运体的结构。这种细菌膜蛋白共同运输钠离子和钾离子;通过将钾离子的运动与钠离子相同方向的有利运动耦合，钾离子被泵送穿过膜，以对抗其化学梯度。在细菌中，这种蛋白质的作用是保持细胞内高浓度的K+并控制细胞膨压。 共转运是一种广泛用于泵送离子或代谢物穿过膜的过程。乳糖通透酶（H+/乳糖同向转运体）的结构为代谢物的同向转运提供了一个很好的通用三维模型。事实上，它的结构与一种相关蛋白质的结构非常相似，即甘油-3-磷酸转运蛋白，这是一种磷酸/糖反向转运蛋白。 我们提出的研究将提供结构和机制的信息，这将是普遍相关的离子共输的研究。对于离子同向转运，有一些研究指出了乳糖通透酶和甘油-3-磷酸转运蛋白所证明的可变可及性模型的替代机制。在这种替代机制中，离子A的结合将改变离子B在另一结合位点的亲和力，而不改变本体溶液的可及性。使用这种机制的蛋白质将与离子通道共享一些结构特征，特别是离子孔的存在。事实上，已经提出这些共转运蛋白将具有KcsA钾通道中存在的相同的一般结构，更具体地说，是（TM螺旋-孔螺旋-TM螺旋）基序的重复。 我们希望Na+/K+同向转运体结构的确定将有助于运输机制的定义。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In this experiment we aim at determining the structure of a Na+/K+ symporter. This bacterial membrane protein co-transports sodium and potassium ions; potassium ions are pumped across a membrane against their chemical gradient by coupling their movement to the favorable movement in the same direction of sodium ions. In the bacteria the role of this protein is to keep a high concentration of K+ inside the cell and to control cell turgor. Symport is a widespread process used for the pumping of ions or metabolites across the membrane. The structure of Lactose permease (a H+/lactose symporter) has provided a good general three-dimensional model for metabolite symport. In fact its structure is very similar to the structure of a related protein, the glycerol-3-phosphate transporter, which is a phosphate/sugar antiporter. The study we are proposing will provide structural and mechanistic information that will be of general relevance for the study of ion symport. For ion symport there are some studies pointing to an alternative mechanism to the variable-accessibility model demonstrated by lactose permease and glycerol-3-phosphate transporter. In this alternative mechanism binding of ion A will alter the affinity for ion B at another binding site without changing the accessibility from bulk solution. Proteins using this mechanism will share some structural characteristics with ion channels, in particular the existence of an ion pore. In fact it has been proposed that these symporters will have the same general architecture present in the KcsA potassium channel, more specifically, a repeat of the (TM helix-pore helix-TM helix) motif. We hope that the determination of the structure of the Na+/K+ symporter will help in the definition of transport mechanism.