Könnyű Balázs, Szilágyi András, Czárán Tamás
Department of Plant Systematics, Ecology and Theoretical Biology, Institute of Biology, Eötvös University, Budapest, Hungary.
MTA-ELTE Theoretical Biology and Evolutionary Ecology Research Group, Budapest, Hungary.
Biol Direct. 2015 May 27;10:30. doi: 10.1186/s13062-015-0049-6.
The RNA World hypothesis offers a plausible bridge from no-life to life on prebiotic Earth, by assuming that RNA, the only known molecule type capable of playing genetic and catalytic roles at the same time, could have been the first evolvable entity on the evolutionary path to the first living cell. We have developed the Metabolically Coupled Replicator System (MCRS), a spatially explicit simulation modelling approach to prebiotic RNA-World evolution on mineral surfaces, in which we incorporate the most important experimental facts and theoretical considerations to comply with recent knowledge on RNA and prebiotic evolution. In this paper the MCRS model framework has been extended in order to investigate the dynamical and evolutionary consequences of adding an important physico-chemical detail, namely explicit replicator structure - nucleotide sequence and 2D folding calculated from thermodynamical criteria - and their possible mutational changes, to the assumptions of a previously less detailed toy model.
For each mutable nucleotide sequence the corresponding 2D folded structure with minimum free energy is calculated, which in turn is used to determine the fitness components (degradation rate, replicability and metabolic enzyme activity) of the replicator. We show that the community of such replicators providing the monomer supply for their own replication by evolving metabolic enzyme activities features an improved propensity for stable coexistence and structural adaptation. These evolutionary advantages are due to the emergent uniformity of metabolic replicator fitnesses imposed on the community by local group selection and attained through replicator trait convergence, i.e., the tendency of replicator lengths, ribozyme activities and population sizes to become similar between the coevolving replicator species that are otherwise both structurally and functionally different.
In the most general terms it is the surprisingly high extra viability of the metabolic replicator system that the present model adds to the MCRS concept of the origin of life. Surface-bound, metabolically coupled RNA replicators tend to evolve different, enzymatically active sites within thermodynamically stable secondary structures, and the system as a whole evolves towards the robust coexistence of a complete set of such ribozymes driving the metabolism producing monomers for their own replication.
RNA世界假说为从无生命状态到前生物地球生命的转变提供了一个合理的桥梁，该假说认为RNA是唯一已知的能够同时发挥遗传和催化作用的分子类型，它可能是通往第一个活细胞进化路径上的首个可进化实体。我们开发了代谢耦合复制子系统（MCRS），这是一种用于模拟矿物表面前生物RNA世界进化的空间显式模拟建模方法，在该方法中，我们纳入了最重要的实验事实和理论考量，以符合有关RNA和前生物进化的最新知识。在本文中，MCRS模型框架得到了扩展，以便研究在一个先前细节较少的简化模型假设中加入一个重要的物理化学细节（即明确的复制子结构——根据热力学标准计算的核苷酸序列和二维折叠结构）及其可能的突变变化所带来的动力学和进化后果。
对于每个可变的核苷酸序列，计算出具有最小自由能的相应二维折叠结构，进而用其来确定复制子的适应性组成部分（降解率、复制能力和代谢酶活性）。我们表明，通过进化代谢酶活性为自身复制提供单体供应的此类复制子群落，具有更高的稳定共存和结构适应倾向。这些进化优势归因于局部群体选择施加于群落的代谢复制子适应性的涌现一致性，并通过复制子性状趋同实现，即共同进化的复制子物种之间在结构和功能上原本不同，但它们的长度、核酶活性和种群大小趋于相似。
最概括地说，本模型为生命起源的MCRS概念增添的是代谢复制子系统惊人的高额外生存能力。表面结合的、代谢耦合的RNA复制子倾向于在热力学稳定的二级结构内进化出不同的酶活性位点，并且整个系统朝着驱动代谢产生自身复制所需单体的一整套此类核酶的稳健共存方向进化。
