Origin of first cells at terrestrial, anoxic geothermal fields
Origin of first cells at terrestrial, anoxic geothermal fields
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DOI：
10.1073/pnas.1117774109
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发表时间：
2012-04-03
影响因子：
11.1
通讯作者：
Koonin, Eugene V.
中科院分区：
文献类型：
--
作者：
Mulkidjanian, Armen Y.;Bychkov, Andrew Yu.;Koonin, Eugene V.
所有细胞都含有比现代（或重建的原始）海洋、湖泊或河流更多的钾、磷酸盐和过渡金属。细胞通过使用复杂的能量依赖性膜酶（膜泵）来维持离子梯度，这些酶嵌入在精心制作的不透离子膜中。第一代细胞既不具备不透离子的膜，也不具备膜泵，因此原始细胞内的无机小分子和离子的浓度与其环境中的无机小分子和离子的浓度保持平衡。因此，现代细胞的离子组成可能反映了原始细胞栖息地的无机离子组成。我们试图重建的“孵化场”的第一个细胞相结合的地球化学分析与现代细胞的通用组件的无机离子的要求的基因组学审查。这些普遍存在的，并通过推断原始的，蛋白质和功能系统显示亲和力和功能的K+，Zn 2+，Mn 2+，和磷酸盐的要求。因此，原始细胞必须在具有高K+/Na+比率和相对高浓度的Zn、Mn和磷化合物的栖息地中进化。地球化学重建表明，有利于细胞起源的离子成分不可能存在于海洋环境中，但与内陆地热系统的蒸汽为主的区域的排放是兼容的。在缺氧、二氧化碳占主导地位的原始大气中，地热田盆地的化学性质类似于现代细胞的内部环境。前细胞阶段的演变可能发生在浅池的冷凝和冷却的地热蒸汽内衬多孔硅酸盐矿物混合金属硫化物和丰富的K+，Zn 2+，和磷化合物。
All cells contain much more potassium, phosphate, and transition metals than modern (or reconstructed primeval) oceans, lakes, or rivers. Cells maintain ion gradients by using sophisticated, energy-dependent membrane enzymes (membrane pumps) that are embedded in elaborate ion-tight membranes. The first cells could possess neither ion-tight membranes nor membrane pumps, so the concentrations of small inorganic molecules and ions within protocells and in their environment would equilibrate. Hence, the ion composition of modern cells might reflect the inorganic ion composition of the habitats of protocells. We attempted to reconstruct the "hatcheries" of the first cells by combining geochemical analysis with phylogenomic scrutiny of the inorganic ion requirements of universal components of modern cells. These ubiquitous, and by inference primordial, proteins and functional systems show affinity to and functional requirement for K+, Zn2+, Mn2+, and phosphate. Thus, protocells must have evolved in habitats with a high K+/Na+ ratio and relatively high concentrations of Zn, Mn, and phosphorous compounds. Geochemical reconstruction shows that the ionic composition conducive to the origin of cells could not have existed in marine settings but is compatible with emissions of vapor-dominated zones of inland geothermal systems. Under the anoxic, CO2-dominated primordial atmosphere, the chemistry of basins at geothermal fields would resemble the internal milieu of modern cells. The precellular stages of evolution might have transpired in shallow ponds of condensed and cooled geothermal vapor that were lined with porous silicate minerals mixed with metal sulfides and enriched in K+, Zn2+, and phosphorous compounds.