Primordial soup or vinaigrette: did the RNA world evolve at acidic pH?
Primordial soup or vinaigrette: did the RNA world evolve at acidic pH?
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DOI：
10.1186/1745-6150-7-4
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发表时间：
2012-01-20
期刊：
影响因子：
5.5
通讯作者：
Tate WP
中科院分区：
文献类型：
--
作者：
Bernhardt HS;Tate WP
RNA世界的概念在生命起源科学界得到了广泛的支持，尽管肯定不是一致的。一种观点认为，生命可能早在43亿至38亿年前的冥古宙就已经出现，当时的大气中含有高浓度的二氧化碳，产生了pH值为3.5至6的酸性海洋。与这种情况相适应的是一个有趣的提议，即生命出现在碱性（pH 9-11）深海热液喷口中，如“失落之城”，与酸性海洋的界面产生了足以驱动第一次新陈代谢的质子梯度。然而，RNA在pH 4-5时最稳定，在碱性pH下不稳定，这增加了RNA可能首先出现在酸性海洋本身（可能靠近酸性热液喷口）、酸性火山湖或彗星池塘的可能性。随着冥古宙的进展，海洋pH值被推断为随着大气CO2水平的下降而逐渐上升到接近中性。我们建议，RNA是非常适合的世界在酸性pH值的演变。这是支持的增强稳定性，在酸性pH值的不仅是RNA磷酸二酯键，但也氨酰-（t）RNA和肽键。最近已经记录了在酸性pH下具有活性的体外选择的核酶的实例。随后向DNA基因组的转变可能部分是由海洋pH值的逐渐上升驱动的，因为DNA在碱性pH值下比RNA具有更大的稳定性，但在酸性pH值下则不然。（i）半质子化的富含胞嘧啶的寡核苷酸的非酶促RNA复制，和（ii）通过螺旋氨酰茎和单链氨酰化核酶之间的三螺旋相互作用进行tRNA/发夹的特异性氨酰化。我们的假设对RNA在碱性热液喷口附近进化的假设提出了质疑。RNA在酸性pH下形成质子化碱基对和三联体的能力表明，标准碱基配对可能不是早期RNA世界的主要要求。本文由尤金·库宁、安东尼·普尔和查尔斯·卡特（由大卫·阿德尔提名）审阅。
The RNA world concept has wide, though certainly not unanimous, support within the origin-of-life scientific community. One view is that life may have emerged as early as the Hadean Eon 4.3-3.8 billion years ago with an atmosphere of high CO2 producing an acidic ocean of the order of pH 3.5-6. Compatible with this scenario is the intriguing proposal that life arose within alkaline (pH 9-11) deep-sea hydrothermal vents like those of the 'Lost City', with the interface with the acidic ocean creating a proton gradient sufficient to drive the first metabolism. However, RNA is most stable at pH 4-5 and is unstable at alkaline pH, raising the possibility that RNA may have first arisen in the acidic ocean itself (possibly near an acidic hydrothermal vent), acidic volcanic lake or comet pond. As the Hadean Eon progressed, the ocean pH is inferred to have gradually risen to near neutral as atmospheric CO2 levels decreased. We propose that RNA is well suited for a world evolving at acidic pH. This is supported by the enhanced stability at acidic pH of not only the RNA phosphodiester bond but also of the aminoacyl-(t)RNA and peptide bonds. Examples of in vitro-selected ribozymes with activities at acid pH have recently been documented. The subsequent transition to a DNA genome could have been partly driven by the gradual rise in ocean pH, since DNA has greater stability than RNA at alkaline pH, but not at acidic pH. We have proposed mechanisms for two key RNA world activities that are compatible with an acidic milieu: (i) non-enzymatic RNA replication of a hemi-protonated cytosine-rich oligonucleotide, and (ii) specific aminoacylation of tRNA/hairpins through triple helix interactions between the helical aminoacyl stem and a single-stranded aminoacylating ribozyme. Our hypothesis casts doubt on the hypothesis that RNA evolved in the vicinity of alkaline hydrothermal vents. The ability of RNA to form protonated base pairs and triples at acidic pH suggests that standard base pairing may not have been a dominant requirement of the early RNA world. This article was reviewed by Eugene Koonin, Anthony Poole and Charles Carter (nominated by David Ardell).
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