Isolation and Functional Characterization of Ca2+/H+ Antiporters from Cyanobacteria*
Isolation and Functional Characterization of Ca2+/H+ Antiporters from Cyanobacteria*
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DOI：
10.1074/jbc.m310282200
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发表时间：
2004-02
影响因子：
4.8
通讯作者：
Rungaroon Waditee;G. S. Hossain;Yoshito Tanaka;Tatsunosuke Nakamura;M. Shikata;J. Takano;T. Takabe;T. Takabe
中科院分区：
文献类型：
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作者：
Rungaroon Waditee;G. S. Hossain;Yoshito Tanaka;Tatsunosuke Nakamura;M. Shikata;J. Takano;T. Takabe;T. Takabe
蓝藻聚球藻基因组序列分析。PCC 6803，鱼腥藻(Anabaena sp.)PCC7120和长链球菌属BP-1的研究表明，这些微生物中只存在单一的钙/氢逆向转运蛋白。在这里，我们从集胞藻中分离到了可能的钙/氢逆向转运蛋白基因。PcC6803(SynCAX)，以及耐盐蓝细菌Aphanothess halophytica(ApCAX)的同源基因。与植物液泡型CAX不同，全长的apCAX和synCAX基因补充了大肠杆菌突变体的钙敏感表型。在碱性条件下，ApCAX和SynCAX蛋白能特异性地催化钙/氢交换反应。免疫学分析表明它们定位于质膜。聚球藻。经SynCAX破坏的PCC6803细胞表现出较低的钙外流活性和盐敏感表型。过表达ApCAX和SynCAX提高了聚球藻的耐盐性。PCC7942细胞。突变分析表明，跨膜片段中两个保守的酸性氨基酸残基Glu-74和Glu-324对交换活性具有重要意义。这些结果清楚地表明，蓝藻在其质膜上含有一个钙/氢逆向转运蛋白，这在耐盐性中起着重要的作用。
Genome sequences of cyanobacteria, Synechocystis sp. PCC 6803, Anabaena sp. PCC 7120, and Thermosynechococcus elongatus BP-1 revealed the presence of a single Ca2+/H+ antiporter in these organisms. Here, we isolated the putative Ca2+/H+ antiporter gene from Synechocystis sp. PCC 6803 (synCAX) as well as a homologous gene from a halotolerant cyanobacterium Aphanothece halophytica (apCAX). In contrast to plant vacuolar CAXs, the full-length apCAX and synCAX genes complemented the Ca2+-sensitive phenotype of an Escherichia coli mutant. ApCAX and SynCAX proteins catalyzed specifically the Ca2+/H+ exchange reaction at alkaline pH. Immunological analysis suggested their localization in plasma membranes. The Synechocystis sp. PCC 6803 cells disrupted of synCAX exhibited lower Ca2+ efflux activity and a salt-sensitive phenotype. Overexpression of ApCAX and SynCAX enhanced the salt tolerance of Synechococcus sp. PCC 7942 cells. Mutagenesis analyses indicate the importance of two conserved acidic amino acid residues, Glu-74 and Glu-324, in the transmembrane segments for the exchange activity. These results clearly indicate that cyanobacteria contain a Ca2+/H+ antiporter in their plasma membranes, which plays an important role for salt tolerance.