Mineral-Promoted RNA Polymerization: Investigating Structural Properties of Catalytic Minerals

这项拟议工作的目标是通过促进从简单的起始前体分子(单体)形成较长的核糖核酸(RNA)分子(聚合物)来识别可能在地球早期生命起源(OOL)中发挥作用的矿物。在生命和酶之前，有人认为矿物可能起到了催化剂的作用，发挥了酶的促进聚合作用。RNA是生物学中最重要的分子之一，因为它具有多种功能。在OOL中，聚合物的形成是重要的，因为低聚物具有呈现不同结构和功能的能力。因此，单体聚合是从简单的有机前体向最早的类生命细胞发展的关键一步。这项拟议的工作将有助于美国国家科学基金会在人类提出的最深刻的问题之一--生命是如何开始的--中促进基础科学进步的目标。拟议的工作还包括许多外联活动，包括编制国家公共广播电台每周节目和一系列公共科学讲座，将科学带给普通公众，以及鼓励妇女和多样性的外联活动。这笔拨款将用于支持一名博士后研究人员。因此，这项拟议的工作也支持了NSF支持教育和多样性以及培训未来科学工作者的目标。矿物由于其反应性和无处不在的特性，很可能在从益生生物地球化学向生物化学的转变中促成了生命的起源。RNA是一种信息载体，一些RNA还可以作为酶，因此在生命起源时，RNA被认为是DNA和酶的先驱。该领域的主要挑战之一是非酶(益生素)合成RNA低聚物，长期以来，矿物被认为是益生素催化剂。蒙脱石在镁或高浓度碱性阳离子存在下促进活性核苷酸聚合的作用已有30年的历史，一些研究也研究了RNA单体在矿物上的吸附，但其他催化矿物尚不清楚。因此，对矿物结构和聚合催化效率之间的任何潜在关系缺乏了解。我们建议解决我们知识中的这一差距。对于矿物结构、吸附能力和催化效率之间的关系，我们提出了三个假设：(1)吸附的核糖核苷酸构象比矿物的吸附能力更重要；(2)二价阳离子或碱性阳离子应该在核苷酸和任何带负电荷的矿物表面形成外球三元络合物，以便它们容易被取代，并且核苷酸磷酸仍然可以用于磷酸化；(3)矿物应该提供一个纳米受限环境，在这个环境中，即使在大体积水环境中，缩合反应也可以发生。特定的矿物，如水钠长石、水滑石和沸石被预测具有催化结构。本研究的主要目标是阐明矿物结构、表面化学、吸附容量、吸附构象和聚合效率之间的潜在关系，从而发现新的催化矿物。其具体目的是(1)确定在没有和存在溶解阳离子的情况下腺苷单磷酸核苷酸的吸附特性；(2)确定各种矿物的核苷酸促进聚合能力；(3)确定吸附的单核苷酸在促进聚合的矿物上的详细分子水平构象；以及(4)合成这些结果，以开发解释蒙脱石催化能力的模型，并测试特定矿物的预测催化活性。我们将使用UV-Vis分光光度法来确定单核苷酸在已知催化矿物和新预测矿物上的吸附，并通过高效液相色谱和MALDI-TOF质谱仪来确定单核苷酸在这些矿物上的聚合。吸附单体的构象将通过魔角旋转核磁共振光谱和傅里叶变换红外光谱来确定。这项拟议的工作提供了基于结构的催化活性预测，从而有助于识别蒙脱石以外的新催化矿物。对特定环境条件下更广泛种类的催化矿物的了解将有助于预测生物分子的益生聚合反应在其他固体世界(例如火星)上出现的可能性。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The goal of the proposed work is to identify minerals which could have played a role in the origin of life (OoL) on early Earth by promoting the formation of longer molecules (polymers) of ribonucleic acid (RNA) from simple starting precursor molecules (monomers). Before life and enzymes, it is proposed that minerals may have acted as catalysts to play the role of enzymes in promoting polymerization. RNA is one of the most important molecules in biology because of its ability to play many roles. In the OoL, the formation of polymers is important because oligomers have the ability to take on different structures and functionalities. Thus, polymerization of monomers is a key bridging step in the progress from simple organic precursors towards the earliest life-like cells. The proposed work would contribute to NSF's goal of promoting the progress of fundamental science in one of the most profound questions asked by humankind, which is, how did life begin? The proposed work also includes numerous outreach activities, including the development of a weekly program on National Public Radio as well as a public science lecture series, which would bring science to the general public, and outreach activities to encourage women and diversity. The grant funds would support a post-doctoral researcher. Thus, the proposed work also supports NSF's goal of supporting education and diversity, and training the future scientific workforce.Minerals, because of their reactivity and ubiquity, likely contributed to the origin of life in the transformation from prebiotic geochemistry to biochemistry. RNA is an information- carrier and some RNAs can also act as enzymes, so RNA is believed to have been a precursor to DNA and enzymes in the origins of life. One of the major challenges in the field is the non-enzymatic (prebiotic) synthesis of RNA oligomers, and minerals have long been proposed as prebiotic catalysts. The role of montmorillonite in promoting polymerization of activated ribonucleotides in the presence of magnesium or high concentrations of alkali cations has been known for thirty years, and several studies have investigated RNA monomer adsorption on minerals, but other catalytic minerals are not known. Thus, there is a lack of knowledge about any potential relationships between mineral structure and polymerization catalytic efficiency. We propose to address this gap in our knowledge. We propose three hypotheses for the relationship between the mineral structure, its adsorption capacity and its catalytic efficiency: (1) adsorbed ribonucleotide conformation is more important than adsorption capacity of the mineral for catalysis; (2) the divalent or alkali cations should form outer-sphere ternary complexes between the nucleotide and any negatively charged mineral surface, so that they can be easily displaced and the nucleotide phosphate is still available for phosphorylation; and (3) the mineral should provide a nanoconfined environment where the condensation reaction can occur despite bulk aqueous environment. Specific minerals, such as birnessite, hydrotalcite and zeolites are predicted to have catalytic structures. The broad goals of the present study are to shed light on any potential relationships between mineral structure, surface chemistry, adsorption capacity, adsorbed conformation and polymerization efficiency, thus, discovering new catalytic minerals. The specific aims are (1) to determine the adsorption characteristics of adenosine monophosphate nucleotides in the absence and presence of dissolved cations;(2) to determine the nucleotide polymerization-promoting ability of various minerals; (3) to determine the detailed molecular-level conformation of adsorbed mononucleotides on minerals that promote polymerization; and (4) to synthesize these results to develop a model for explaining the catalytic ability of montmorillonite and to test the predicted catalytic activity of specific minerals. We will determine adsorption using UV-Vis spectrophotometry, and polymerization of mononucleotides on the known catalytic mineral and on the newly predicted minerals by High Performance Liquid Chromatography (HPLC) and MALDI-TOF Mass Spectrometry. Conformation of adsorbed monomer will be determined by Magic Angle Spinning NMR spectroscopy and by Fourier Transform Infra-Red Spectroscopy. The proposed work provides structure-based predictions for catalytic activity, thus helping to identify new catalytic minerals beyond montmorillonite. Knowledge of a wider variety of catalytic minerals under specific environmental conditions will help predict the plausibility of prebiotic polymerization reactions of biomolecules for life's emergence on other solid worlds, e.g., Mars.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.