施一公2014-04-14 5:00 PM

氨基酸逆向转运蛋白的结构与机制  Structure and Mechanism of an Amino Acid Antiporter. 

论文摘要
致命的肠道致病菌,例如大肠杆菌菌株O157:H7,依靠耐酸性(AR)系统而得以生存在胃部酸性环境中。耐酸性的重要组成部分是一个依赖精氨酸的精氨酸:即能排出细胞内质子的胍丁胺逆向转运蛋白。在此我们展示AdiC精氨酸的晶体结构:即源自O157:H7的胍丁胺逆向转运蛋白以及在3.6Å分辨率下转运蛋白氨基酸/多胺/ 有机组织(APC)超家族的成员。这一整体折叠类似于多个Na +-耦合协同载体的整体折叠。AdiC包含12个跨膜片段,形成同源二聚体,并且存在于晶体内外向开放的构象中。保守性酸性凹囊向周质开放。结构和生化分析揭示了主要配体结合残基,定义了传输路径,并为逆向转运蛋白的活性提出了保守性机制。
Abstract
Virulent enteric pathogens such as Escherichia coli strain O157:H7 rely on acid-resistance (AR) systems to survive the acidic environment in the stomach. A major component of AR is an arginine-dependent arginine:agmatine antiporter that expels intracellular protons. Here, we report the crystal structure of AdiC, the arginine:agmatine antiporter from E. coli O157:H7 and a member of the amino acid/polyamine/organocation (APC) superfamily of transporters at 3.6 Å resolution. The overall fold is similar to that of several Na+-coupled symporters. AdiC contains 12 transmembrane segments, forms a homodimer, and exists in an outward-facing, open conformation in the crystals. A conserved, acidic pocket opens to the periplasm. Structural and biochemical analysis reveals the essential ligand-binding residues, defines the transport route, and suggests a conserved mechanism for the antiporter activity.

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