Na+-dependent K+ uptake ktr system from the cyanobacterium Synechocystis sp PCC 6803 and its role in the early phases of cell adaptation to hyperosmotic shock
Na+-dependent K+ uptake ktr system from the cyanobacterium Synechocystis sp PCC 6803 and its role in the early phases of cell adaptation to hyperosmotic shock
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DOI：
10.1074/jbc.m407268200
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发表时间：
2004-12-24
影响因子：
4.8
通讯作者：
Uozumi, N
中科院分区：
文献类型：
--
作者：
Matsuda, N;Kobayashi, H;Uozumi, N
跨膜离子转运过程在细胞适应高渗条件中起着关键作用。以前的工作表明，在蓝藻集胞藻PCC 6803中的ktrB/ntpJ样推定的Na+/K+转运蛋白基因的破坏赋予增加的Na+敏感性，并抑制HCO 3-吸收。在这里，我们报告的机制基础上，这种效果。在大肠杆菌中的异源表达实验表明，三个集胞藻基因是K+转运活性所必需的。它们编码NAD（+）结合外周膜蛋白（ktrA; sll 0493），这是一种完整的膜蛋白，属于K+转运蛋白超家族（ktrB;以前称为ntpJ; slr 1509），以及一种新类型的ktr基因产物，以前未在Ktr系统中发现（ktrE; slr 1508）。在大肠在大肠杆菌中，集胞藻KtrABE介导的K ~+吸收具有中等的亲和力（K-m约为60 μ M），依赖于Na ~+和高膜电位，但不依赖于ATP。KtrABE既不介导Na+摄取，也不介导Na+流出。在集胞藻PCC 6803中，KtrB介导的K+吸收需要Na+，并被质子载体抑制。DeltaktrB菌株对NaCl或山梨醇引起的长期高渗胁迫敏感。高渗休克最初导致细胞净K+的损失。用山梨醇休克的DeltaktrB细胞不能将K+重新积累到其原始水平。这些数据表明，在菌株PCC 6803 K+摄取通过KtrABE起着至关重要的作用，在早期阶段的细胞膨压调节后高渗休克。
Transmembrane ion transport processes play a key role in the adaptation of cells to hyperosmotic conditions. Previous work has shown that the disruption of a ktrB/ntpJ-like putative Na+/K+ transporter gene in the cyanobacterium Synechocystis sp. PCC 6803 confers increased Na+ sensitivity, and inhibits HCO3- uptake. Here, we report on the mechanistic basis of this effect. Heterologous expression experiments in Escherichia coli show that three Synechocystis genes are required for K+ transport activity. They encode an NAD(+)-binding peripheral membrane protein ( ktrA; sll0493), an integral membrane protein, belonging to a superfamily of K+ transporters ( ktrB; formerly ntpJ; slr1509), and a novel type of ktr gene product, not previously found in Ktr systems (ktrE; slr1508). In E. coli, Synechocystis KtrABE-mediated K+ uptake occurred with a moderately high affinity (K-m of about 60 muM), and depended on both Na+ and a high membrane potential, but not on ATP. KtrABE neither mediated Na+ uptake nor Na+ efflux. In Synechocystis sp. PCC 6803, KtrB-mediated K+ uptake required Na+ and was inhibited by protonophore. A DeltaktrB strain was sensitive to long term hyperosmotic stress elicited by either NaCl or sorbitol. Hyperosmotic shock led initially to loss of net K+ from the cells. The DeltaktrB cells shocked with sorbitol failed to reaccumulate K+ up to its original level. These data indicate that in strain PCC 6803 K+ uptake via KtrABE plays a crucial role in the early phase of cell turgor regulation after hyperosmotic shock.