Physiological function of Na^+/K^+ transporters from bacteria and plants

1. 来自拟南芥的AtHKTl （AtHKTl）形成4层膜-孔-膜结构。发现HKT转运体的p环仅在介导K^+选择性的甘氨酸残基之一中表现出同一性。HKT转运蛋白有一个共同的祖先转运蛋白，具有4个环。KATl通道与其他动植物的K^+通道具有典型的相似性。KATl中S3和S4的电压感应片段只有在它们之间发生特异性相互作用时才会在翻译后整合到膜中。插入过程是新近发现的第二种膜蛋白整合过程。细菌Na^+/H^+反转运蛋白跨膜中的天冬氨酸参与H^+的渗透，但不参与Na^+的渗透。AtHKTl在植物维管组织中表达。AtHKTl在植物体内Na^+的再循环中起作用。测定了胞囊菌PCC6803中hkt型转运体K^+的通透性。利用大肠杆菌表达系统，通过Na^+激活K^+转运活性。

1. AtHKTl from Arabidopsis (AtHKTl) was found to form 4-fold membrane-pore-membrane structure.2. It is found that the P-loop of HKT transporters show identity only in one of glycine residues that mediates K^+ selectivity. HKT transporters share a common ancestor transporter with 4-loops.3. KATl shares typical similarity with other animal and plant K^+ channels. The voltage-sensing segments of S3 and S4 in KATl are posttranslationally integrated into the membrane only when specific interation occurs between them. The insertion process is a newly recognized second type of the membrane protein integration process.4. The aspartate in the transmembrane of Na^+/H^+ antiporter from a bacteria involves in H^+ permeation but not Na^+ permeation.5. The AtHKTl was expressed in vascular tissue in plant.6. AtHKTl plays a role in the recirculation of Na^+ in plant body.7. The K^+ permeation of HKT-type transporter in Synechocystis PCC6803 was measured. K^+ transport activity was activated by Na^+ using E. coli expression system.