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

1.拟南芥AtHKT1(AtHKT1)形成四重膜-孔-膜结构。研究发现，HKT转运蛋白的P-环仅在介导K~+选择性的甘氨酸残基中有相同之处。HKT转运体与4-LOOP共用一个祖先转运体。KAT1与其他动植物K~(++)通道具有典型的相似性。KAT1中的S3和S4的电压敏感片段只有在它们之间发生特定的相互作用时才被翻译后整合到膜上。插入过程是新发现的第二种膜蛋白整合过程。细菌Na~+/H~+逆向转运蛋白跨膜上的天冬氨酸参与H~+渗透，而不参与Na~+渗透。AtHKT1在植物维管组织中有表达。ATHKT1在植物体内Na~+的再循环中起作用。测定了HKT型转运蛋白在集胞藻PCC6803中的K~(+)渗透量。利用大肠杆菌表达系统，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.