Plasma Membrane Aquaporin AqpZ Protein Is Essential for Glucose Metabolism during Photomixotrophic Growth of Synechocystis sp PCC 6803
Plasma Membrane Aquaporin AqpZ Protein Is Essential for Glucose Metabolism during Photomixotrophic Growth of Synechocystis sp PCC 6803
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DOI：
10.1074/jbc.m111.236380
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发表时间：
2011-07-15
影响因子：
4.8
通讯作者：
Uozumi, Nobuyuki
中科院分区：
文献类型：
--
作者：
Akai, Masaro;Onai, Kiyoshi;Uozumi, Nobuyuki
集胞藻 PCC 6803 的基因组包含编码水通道蛋白 aqpZ 的单个基因。 AqpZ 蛋白在质膜中充当透水通道。然而，AqpZ 在集胞藻中的生理重要性仍不清楚。我们发现含葡萄糖培养基中的生长抑制了 Delta aqpZ 细胞的正常分裂并导致细胞死亡。 Delta aqpZ 背景中编码葡萄糖转运蛋白的基因的缺失减轻了葡萄糖介导的 Delta aqpZ 细胞的生长抑制。添加葡萄糖后，Delta aqpZ 细胞比野生型细胞膨胀更多，表明细胞质渗透压增加。这伴随着磷酸戊糖途径的下调和同时的糖原积累。通过 GC/TOF-MS 对野生型和 Delta aqpZ 细胞进行的代谢分析显示，突变体中三羧酸循环中间体和某些氨基酸相对减少。代谢物水平的变化可能是观察到 Delta aqpZ 细胞生长速率下降以及 pH 值范围为 7.5 至 8.5 时 PSII 活性下降的原因。编码假定转录因子的 sll1961 突变体和缺乏假定葡萄糖感应激酶的 Delta hik31 突变体均表现出比 Delta aqpZ 细胞更高的葡萄糖敏感性。蛋白质表达的检查表明 sll1961 作为 aqpZ 基因表达的正调节因子发挥作用，但不是唯一的调节因子。总体而言，Delta aqpZ 细胞在光合营养条件下显示出大量营养素代谢、pH 稳态和细胞分裂方面的缺陷，这与 AqpZ 在葡萄糖代谢中的重要作用一致。
The genome of Synechocystis PCC 6803 contains a single gene encoding an aquaporin, aqpZ. The AqpZ protein functioned as a water-permeable channel in the plasma membrane. However, the physiological importance of AqpZ in Synechocystis remains unclear. We found that growth in glucose-containing medium inhibited proper division of Delta aqpZ cells and led to cell death. Deletion of a gene encoding a glucose transporter in the Delta aqpZ background alleviated the glucose-mediated growth inhibition of the Delta aqpZ cells. The Delta aqpZ cells swelled more than the wild type after the addition of glucose, suggesting an increase in cytosolic osmolarity. This was accompanied by a down-regulation of the pentose phosphate pathway and concurrent glycogen accumulation. Metabolite profiling by GC/TOF-MS of wild-type and Delta aqpZ cells revealed a relative decrease of intermediates of the tricarboxylic acid cycle and certain amino acids in the mutant. The changed levels of metabolites may have been the cause for the observed decrease in growth rate of the Delta aqpZ cells along with decreased PSII activity at pH values ranging from 7.5 to 8.5. A mutant in sll1961, encoding a putative transcription factor, and a Delta hik31 mutant, lacking a putative glucose-sensing kinase, both exhibited higher glucose sensitivity than the Delta aqpZ cells. Examination of protein expression indicated that sll1961 functioned as a positive regulator of aqpZ gene expression but not as the only regulator. Overall, the Delta aqpZ cells showed defects in macronutrient metabolism, pH homeostasis, and cell division under photomixotrophic conditions, consistent with an essential role of AqpZ in glucose metabolism.