Plant-specific cation/H+ exchanger 17 and its homologs are endomembrane K+ transporters with roles in protein sorting.
Plant-specific cation/H+ exchanger 17 and its homologs are endomembrane K+ transporters with roles in protein sorting.
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DOI：
10.1074/jbc.m111.252650
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发表时间：
2011-09-30
期刊：
影响因子：
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通讯作者：
Sze H
中科院分区：
文献类型：
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作者：
Chanroj S;Lu Y;Padmanaban S;Nanatani K;Uozumi N;Rao R;Sze H
真核细胞中细胞内区室的复杂性不断演化，提供了独特的环境来调节细胞增殖和存活所需的过程。预测的阳离子/质子交换器 (CHX) 大家族（以拟南芥中的 28 个基因为代表）与植物的不同内膜区室和组织相关，尽管人们对它们的作用知之甚少。我们在被设计为缺乏多种阳离子处理机制的酵母和细菌细胞中表达了由 CHX15-CHX20 编码的系统发育相关的 CHX 基因簇。其中，CHX16–CHX20 与 pH 稳态有关，因为它们的表达挽救了宿主酵母菌株的碱性 pH 敏感生长表型。较小的子集 CHX17–CHX19 也具有对潮霉素 B 的耐受性。在 K+- 和低 pH 依赖性生长表型中观察到进一步的差异。尽管 CHX17 不会改变酵母中的细胞质或液泡 pH 值，但 CHX20 分别引起细胞质和液泡的酸化和碱化。利用缺乏 K+ 摄取系统的大肠杆菌菌株中的异源表达，我们为 CHX17 和 CHX20 介导的 K+ (86Rb) 转运提供了证据。最后，我们通过在碱性 pH 下生长的酵母突变体中羧肽酶 Y 的分泌来测量，表明 CHX17 和 CHX20 影响蛋白质分选。在植物细胞中，CHX20-RFP 与内质网标记物共定位，而 RFP 标记的 CHX17-CHX19 与液泡前区室和内体标记物共定位。总之，这些结果表明，为了响应环境信号，多个 CHX 转运蛋白差异调节不同细胞内区室的 K+ 和 pH 稳态，这改变了可能对适应和生存至关重要的膜运输事件。
The complexity of intracellular compartments in eukaryotic cells evolved to provide distinct environments to regulate processes necessary for cell proliferation and survival. A large family of predicted cation/proton exchangers (CHX), represented by 28 genes in Arabidopsis thaliana, are associated with diverse endomembrane compartments and tissues in plants, although their roles are poorly understood. We expressed a phylogenetically related cluster of CHX genes, encoded by CHX15–CHX20, in yeast and bacterial cells engineered to lack multiple cation-handling mechanisms. Of these, CHX16–CHX20 were implicated in pH homeostasis because their expression rescued the alkaline pH-sensitive growth phenotype of the host yeast strain. A smaller subset, CHX17–CHX19, also conferred tolerance to hygromycin B. Further differences were observed in K+- and low pH-dependent growth phenotypes. Although CHX17 did not alter cytoplasmic or vacuolar pH in yeast, CHX20 elicited acidification and alkalization of the cytosol and vacuole, respectively. Using heterologous expression in Escherichia coli strains lacking K+ uptake systems, we provide evidence for K+ (86Rb) transport mediated by CHX17 and CHX20. Finally, we show that CHX17 and CHX20 affected protein sorting as measured by carboxypeptidase Y secretion in yeast mutants grown at alkaline pH. In plant cells, CHX20-RFP co-localized with an endoplasmic reticulum marker, whereas RFP-tagged CHX17–CHX19 co-localized with prevacuolar compartment and endosome markers. Together, these results suggest that in response to environmental cues, multiple CHX transporters differentially modulate K+ and pH homeostasis of distinct intracellular compartments, which alter membrane trafficking events likely to be critical for adaptation and survival.