Water fluxes through membrane transport proteins

每个生物细胞都被含有多种蛋白质的脂质膜所包围，这些蛋白质使细胞能够保持稳定的细胞内内容物，同时能够与外部世界交流。很明显，由于包括细胞生长在内的几个原因，该膜需要是水可渗透的。在20世纪50年代，人们逐渐认识到，除了水通过脂质双层扩散之外，水运动的很大一部分是通过膜蛋白。其中一种膜蛋白最终在1992年被鉴定出来，并被Peter Agree命名为“水通道蛋白”，Peter Agree因这一发现于2003年获得诺贝尔化学奖。有趣的是，用于介导葡萄糖转运的其他类型的膜蛋白也被发现是透水性的，但它们的这方面性质尚未详细研究。本研究计划旨在了解不同转运蛋白的水渗透性所发挥的作用。一方面，它是可能的，运输蛋白质有助于显着的宏观膜透水性。另一方面，通过转运蛋白的水通量的存在也可能旨在增加溶质转运的效率。 在接下来的5年里，我们想回答关于这个问题的4个一般性问题。#1）转运蛋白介导的水通量的生理重要性是什么？我们计划研究卵母细胞中表达的20多种不同的转运蛋白。我们还将使用来自肾脏和肠的刷状缘膜囊泡以及几种细胞系研究天然膜。#2）水渗透途径的生物物理特性是什么？使用各种小溶质分子，我们将估计水通道的大小。 #3）水通过Na/葡萄糖协同转运蛋白（SGLT 1）的分子途径是什么？ vSGLT（SGLT 1的细菌同源物）的晶体结构将用于识别一系列可以接受水分子并共同构成水通路的位点。最后，#4）通过给定转运体的水流的存在如何影响其功能？

Every biological cell is surrounded by a lipid membrane containing a variety of proteins that allow the cell to maintain a stable intracellular content while being able to communicate with the exterior world. It is clear that this membrane needs to be water permeable for several reasons including cell growth. In the 1950's, it was progressively realised that, on top of water diffusion through the lipid bilayer, a significant fraction of the water movement was going through membrane proteins. One of these membrane proteins was finally identified in 1992 and named "aquaporin" by Peter Agree who won the Nobel Prize of chemistry in 2003 for this discovery. Interestingly, other types of membrane proteins which are used to mediate glucose transport were also found to be water permeable but this aspect of their properties has not been studied in details. The present research program is aimed at understanding the role played by the water permeability of different transport proteins. On the one hand, it is possible that transport proteins contribute significantly to the macroscopic membrane water permeability. On the other hand, it is also possible that the presence of a water flux through a transport protein is aimed at increasing the efficiency of solute transport. In the next 5 years, we would like to answer 4 general questions concerning this problem. #1) What is the physiological importance of transporter-mediated water fluxes? We plan to investigate more than 20 different transport proteins expressed in oocytes. We will also study native membrane using brush border membrane vesicles from kidney and intestine as well as several cell lines. #2) What is the biophysical properties of the water permeation pathway? Using a variety of small solute molecules, we will estimate the size of the water pathway. #3) What is the molecular pathway used by water to cross the Na/glucose cotransporter (SGLT1)? The crystal structure of vSGLT (a bacterial homologue of SGLT1) will be used to identify a series of sites that could accept water molecules and, together, constitute a water pathway. Finally, #4) how does the presence of a water flow through a given transporter affect its function?