细菌同源尿素转运蛋白的晶体结构。
Crystal structure of a bacterial homologue of the kidney urea transporter.
机构信息
Department of Physiology & Cellular Biophysics, College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, New York 10032, USA.
出版信息
Nature. 2009 Dec 10;462(7274):757-61. doi: 10.1038/nature08558.
Urea is highly concentrated in the mammalian kidney to produce the osmotic gradient necessary for water re-absorption. Free diffusion of urea across cell membranes is slow owing to its high polarity, and specialized urea transporters have evolved to achieve rapid and selective urea permeation. Here we present the 2.3 A structure of a functional urea transporter from the bacterium Desulfovibrio vulgaris. The transporter is a homotrimer, and each subunit contains a continuous membrane-spanning pore formed by the two homologous halves of the protein. The pore contains a constricted selectivity filter that can accommodate several dehydrated urea molecules in single file. Backbone and side-chain oxygen atoms provide continuous coordination of urea as it progresses through the filter, and well-placed alpha-helix dipoles provide further compensation for dehydration energy. These results establish that the urea transporter operates by a channel-like mechanism and reveal the physical and chemical basis of urea selectivity.
尿素在哺乳动物肾脏中高度浓缩，以产生水重吸收所需的渗透梯度。由于其高极性，尿素在细胞膜中的自由扩散速度较慢，因此进化出了专门的尿素转运体以实现快速和选择性的尿素渗透。在这里，我们展示了来自细菌脱硫弧菌的功能性尿素转运体的 2.3A 结构。该转运体是一个三聚体，每个亚基包含由蛋白质的两个同源半部分形成的连续跨膜孔。该孔包含一个狭窄的选择性过滤器，可容纳几个脱水尿素分子在单链中。骨架和侧链氧原子为尿素在通过过滤器时提供连续的配位，并且放置良好的α-螺旋偶极子为进一步补偿脱水能提供了补偿。这些结果表明，尿素转运体通过通道样机制发挥作用，并揭示了尿素选择性的物理和化学基础。
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