Krulwich Terry A, Hicks David B, Ito Masahiro
Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, NY 10029, USA.
Mol Microbiol. 2009 Oct;74(2):257-60. doi: 10.1111/j.1365-2958.2009.06842.x. Epub 2009 Aug 11.
Most bacterial genomes have five to nine distinct genes predicted to encode transporters that exchange cytoplasmic Na(+) and/or K(+) for H(+) from outside the cell, i.e. monovalent cation/proton antiporters. By contrast, pathogens that live primarily inside host cells usually possess zero to one such antiporter while other stress-exposed bacteria exhibit even higher numbers. The monovalent cation/proton antiporters encoded by these diverse genes fall into at least eight different transporter protein families based on sequence similarity. They enable bacteria to meet challenges of high or fluctuating pH, salt, temperature or osmolarity, but we lack explanations for why so many antiporters are needed and for the value added by specific antiporter types in specific settings. In this issue of Molecular Microbiology, analyses of the pH dependence of cytoplasmic [Na(+)], [K(+)], pH and transmembrane electrical potential in the 'poly extremophile'Natranaerobius thermophilus are the context for assessment of the catalytic properties of 12 predicted monovalent cation/proton antiporters in the genome of this thermophilic haloalkaliphile. The results provide a profile of adaptations of the poly extremophilic anaerobe, including a proposed role of cytoplasmic buffering capacity. They also provide new perspectives on two large monovalent cation/proton antiporter families, the NhaC and the cation/proton antiporter-3 antiporter families.
大多数细菌基因组预计有5至9个不同的基因编码转运蛋白，这些转运蛋白将细胞质中的Na⁺和/或K⁺与细胞外的H⁺进行交换，即单价阳离子/质子反向转运蛋白。相比之下，主要生活在宿主细胞内的病原体通常只有零到一个这样的反向转运蛋白，而其他受到应激的细菌则有更多数量。基于序列相似性，这些不同基因编码的单价阳离子/质子反向转运蛋白至少分为八个不同的转运蛋白家族。它们使细菌能够应对高pH值或波动的pH值、盐、温度或渗透压等挑战，但我们尚不清楚为何需要如此多的反向转运蛋白，以及特定类型的反向转运蛋白在特定环境中所增加的价值。在本期《分子微生物学》中，对“多极端嗜热菌”嗜热栖热放线菌细胞质中[Na⁺]、[K⁺]、pH值和跨膜电势的pH依赖性分析，是评估该嗜热嗜碱菌基因组中12种预测的单价阳离子/质子反向转运蛋白催化特性的背景。研究结果提供了多极端嗜热厌氧菌的适应性概况，包括细胞质缓冲能力的假定作用。它们还为两个大的单价阳离子/质子反向转运蛋白家族，即NhaC和阳离子/质子反向转运蛋白-3反向转运蛋白家族提供了新的视角。
