ION TRANSPORTER

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 在本实验中，我们旨在确定Na+/K+同向转运体的结构。这种细菌膜蛋白共同运输钠和钾离子；钾离子通过将它们的移动与钠离子在同一方向上的有利移动相结合，逆着它们的化学梯度被泵过膜。在细菌中，这种蛋白质的作用是保持细胞内高浓度的K+，并控制细胞膨胀。 Symport是一种广泛使用的过程，用于将离子或代谢物泵过膜。乳糖通透酶(H+/乳糖共转运体)的结构为代谢产物共转运体提供了一个良好的通用三维模型。事实上，它的结构与一种相关蛋白质的结构非常相似，甘油-3-磷酸转运蛋白是一种磷酸/糖逆向转运蛋白。 我们提议的研究将提供结构和机制信息，这些信息将对离子符号的研究具有普遍意义。对于离子转运体，有一些研究指出了乳糖渗透酶和甘油-3-磷酸转运体所证明的可变可及性模型的另一种机制。在这一替代机制中，离子A的结合将改变离子B在另一个结合部位的亲和力，而不改变从本体溶液的可及性。使用这种机制的蛋白质将与离子通道有一些共同的结构特征，特别是离子孔的存在。事实上，有人提出，这些转运体将具有与KCSA钾通道相同的一般结构，更具体地说，是(TM螺旋-孔道螺旋-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确定转运机制。

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.