UV-light-driven prebiotic synthesis of iron–sulfur clusters

Iron–sulfur clusters are ancient cofactors that play a fundamental role in metabolism and may have impacted the prebiotic chemistry that led to life. However, it is unclear whether iron–sulfur clusters could have been synthesized on prebiotic Earth. Dissolved iron on early Earth was predominantly in the reduced ferrous state, but ferrous ions alone cannot form polynuclear iron–sulfur clusters. Similarly, free sulfide may not have been readily available. Here we show that UV light drives the synthesis of [2Fe–2S] and [4Fe–4S] clusters through the photooxidation of ferrous ions and the photolysis of organic thiols. Iron–sulfur clusters coordinate to and are stabilized by a wide range of cysteine-containing peptides and the assembly of iron–sulfur cluster-peptide complexes can take place within model protocells in a process that parallels extant pathways. Our experiments suggest that iron–sulfur clusters may have formed easily on early Earth, facilitating the emergence of an iron–sulfur-cluster-dependent metabolism

Prebiotic Synthesis of Redox-Active Iron-Sulfur Clusters

Iron-sulfur clusters are indispensable to extant metabolism and are thought to have had an ancient role in mediating the chemical reactions that led to life. However, there has been no clear proposal for how these inorganic clusters came to occupy such an important position in biology. In this thesis I describe my efforts in delineating a plausible path from short, prebiotically plausible peptides to longer sequences with similar features to modern day iron-sulfur proteins. Small organic thiolates and short cysteine-containing peptides can give rise to [2Fe-2S] and [4Fe-4S] clusters in aqueous solution when irradiated with UV light in the presence of iron ions. Additionally, duplications of tripeptides coordinated iron-sulfur clusters give sequences which are better able to stabilize iron-sulfur clusters, resembling motifs with cysteinyl ligand spacing highly similar to contemporary ferredoxins. Moreover, the studied iron-sulfur clusters are redox active and are able to mimic extant metabolic pathways, such as the first step of the electron transport chain, within protocells favouring the formation of a proton gradient which could be exploited for central biosynthetic processes

Ring-Opening of Glycerol Cyclic Phosphates Leads to a Diverse Array of Potentially Prebiotic Phospholipids

Phospholipids are the primary constituents of cell membranes across all domains of life, but how and when phospholipids appeared on early Earth remains unknown. Previously described prebiotic pathways leading to complex phospholipids relied upon preexisting substrates, the availability of which on early Earth has yet to be shown. Here we describe potentially prebiotic syntheses of a diverse array of complex phospholipids and their building blocks. Firstly, we show that choline could have been produced on early Earth by stepwise N-methylation of ethanolamine. Secondly, taking a systems chemistry approach, we demonstrate that the intrinsically activated glycerol-2,3-cyclic phosphate undergoes ring-opening with combinations of prebiotic amino alcohols to yield complex phospholipid headgroups. Importantly, this pathway selects for the formation of 2-amino alcohol-bearing phospholipid headgroups and enables the accumulation of their natural regioisomers. Thirdly, we show that dry-state ring-opening of cyclic lysophosphatidic acids leads to a range of self-assembling lysophospholipids. Our results provide new prebiotic routes to key intermediates on the way towards modern phospholipids and illuminate the potential origin and evolution of cell membranes

Glycerol configurations of environmental GDGTs investigated using a selective sn2 ether cleavage protocol

The glycerol configurations of glycerol dialkyl glycerol tetraethers (GDGTs) in environmental samples were investigated using a selective sn2 ether cleavage protocol. Using this procedure, GDGTs with a parallel glycerol configuration afford two types of derivatives, diols and diallylethers, whereas only one kind, monoallylethers, originate from their antiparallel isomers. Isoprenoidal GDGTs from a marine sediment are shown to be predominately parallel based on the distributions of these ether cleavage products. Crenarchaeol and its so-called regioisomer both have parallel configurations with the cyclohexane ring located on the sn3,3 ether bonded tricyclic biphytanyl moiety. A Messel shale sample containing isoprenoidal GDGTs contributed mainly by methanogenic archaea has a substantial portion with the antiparallel configuration. Branched (non-isoprenoidal) GDGTs in both the Messel shale and the marine sediment are mainly antiparallel. This selective sn2 ether cleavage approach provides a potentially powerful analytical tool to investigate not only the exact molecular structures of GDGT constitutional isomers and their biosynthetic pathways but also the heterogeneous inputs of sedimentary GDGT and their isotopic signatures, if different source species synthesize GDGTs with unique glycerol configurations. Further analyses of this type will reveal the glycerol configurations of the GDGTs of a broad range of microbial cultures and environmental samples. Keywords: GDGT; Chemical degradation; Glycerol configuration; Crenarchaeol; Marine sediment; Methanoge

Activation Chemistry Drives the Emergence of Functionalized Protocells

The complexity of the simplest conceivable cell suggests that a systems chemistry approach is required tounderstand and potentially recapitulate the intricate network of prebiotic reactions that led to the emergenceof life. Early cells probably relied upon compatible and interconnected chemistries to link RNA, peptides andmembranes. Here we show that several types of vesicles, formed from prebiotically plausible mixtures ofamphiphiles, allow activation of amino acids, peptides and nucleotides. Interestingly, activation chemistrydrives the advantageous conversion of reactive amphiphiles into inert cyclophospholipids, thus supportingtheir potential role as major constituents of primitive cells. Moreover, activation of prebiotic building blockswithin fatty acid-based vesicles yields lipidated species capable of localizing and functionalizing primitivemembranes. Our findings describe a potentially prebiotic scenario in which the components of primitive cellscould undergo activation, providing new species that might have enabled an increase in the functionality ofemerging cells

Harnessing Chemical Energy for the Activation and Joining of Prebiotic Building Blocks

Simultaneous activation of carboxylates and phosphates provides multiple pathways for the generation of reactive intermediates, including mixed carboxylic acid-phosphoric acid anhydrides, for the synthesis of peptidyl-RNAs, peptides, RNA oligomers and primordial phospholipids. These results indicate that unified prebiotic activation chemistry could have enabled the joining of building blocks in aqueous solution from a common pool and enabled the progression of a system towards higher complexity foreshadowing the modern encapsulated peptide-nucleic acid syste

Activation chemistry drives the emergence of functionalised protocells.

The complexity of the simplest conceivable cell suggests that the chemistry of prebiotic mixtures needs to be explored to understand the intricate network of prebiotic reactions that led to the emergence of life. Early cells probably relied upon compatible and interconnected chemistries to link RNA, peptides and membranes. Here we show that several types of vesicles, composed of prebiotically plausible mixtures of amphiphiles, spontaneously form and sustain the methyl isocyanide-mediated activation of amino acids, peptides and nucleotides. Activation chemistry also drives the advantageous conversion of reactive monoacylglycerol phosphates into inert cyclophospholipids, thus supporting their potential role as major constituents of protocells. Moreover, activation of prebiotic building blocks within fatty acid-based vesicles yields lipidated species capable of localising to and functionalising primitive membranes. Our findings describe a potentially prebiotic scenario in which the components of primitive cells undergo activation and provide new species that might have enabled an increase in the functionality of protocells

Prebiotic iron–sulfur peptide catalysts generate a pH gradient across model membranes of late protocells

Prebiotic chemistry was likely mediated by metals, but how such prebiotic chemistry progressed into the metabolic-like networks needed to sustain life remains unclear. Here we experimentally delineate a potential path from prebiotically plausible iron–sulfur peptide catalysts to the types of pH gradients exploited by all known living organisms. Iron–sulfur peptides cooperatively accept electrons from NADH in a manner that is only partially mediated by ionic interactions. The electrons are then either passed to a terminal electron acceptor, such as hydrogen peroxide, or to an intermediate carrier, such as ubiquinone. The reduction of hydrogen peroxide leads to the production of hydroxide, which then contributes to the formation of a pH gradient across late protocell membranes. The data are consistent with the activity of prebiotic iron–sulfur peptide catalysts providing a selective advantage by equipping protocells with a pathway that connects catabolism to anabolism

Research data in support of "Thermally-driven membrane phase transitions enable content reshuffling in primitive cells"

Representative data set including: turbidity (UV-vis spectrophotometry) traces, fluorescene measurements, and data for statistical analyses, all in csv files, confocal and cryo-EM micrographs (pngs), and epifluorescence time and temperature-resolved movies (mp4). Epifluorescence microscopy movies are compressed for reasons of space, and the raw data are available through the authors.R.R.S also acknowledges funding support from the Mexican National Council for Science and Technology (CONACYT, Grant No. 472427) and the Cambridge Trust. C.B. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie (RNA-Rep, MSCA grant no. 839899) and from the Royal Commission for the Exhibition of 1851. L.D.M. also acknowledges funding from the European Research Council (ERC) under the Horizon 2020 Research and Innovation Programme (ERC-STG No 851667 NANOCELL). D.K.O. acknowledges funding from the Natural Sciences and Engineering Research Council of Canada (NSERC, Early Career Researcher Grant no. 401667)

Thermally Driven Membrane Phase Transitions Enable Content Reshuffling in Primitive Cells.

Self-assembling single-chain amphiphiles available in the prebiotic environment likely played a fundamental role in the advent of primitive cell cycles. However, the instability of prebiotic fatty acid-based membranes to temperature and pH seems to suggest that primitive cells could only host prebiotically relevant processes in a narrow range of nonfluctuating environmental conditions. Here we propose that membrane phase transitions, driven by environmental fluctuations, enabled the generation of daughter protocells with reshuffled content. A reversible membrane-to-oil phase transition accounts for the dissolution of fatty acid-based vesicles at high temperatures and the concomitant release of protocellular content. At low temperatures, fatty acid bilayers reassemble and encapsulate reshuffled material in a new cohort of protocells. Notably, we find that our disassembly/reassembly cycle drives the emergence of functional RNA-containing primitive cells from parent nonfunctional compartments. Thus, by exploiting the intrinsic instability of prebiotic fatty acid vesicles, our results point at an environmentally driven tunable prebiotic process, which supports the release and reshuffling of oligonucleotides and membrane components, potentially leading to a new generation of protocells with superior traits. In the absence of protocellular transport machinery, the environmentally driven disassembly/assembly cycle proposed herein would have plausibly supported protocellular content reshuffling transmitted to primitive cell progeny, hinting at a potential mechanism important to initiate Darwinian evolution of early life forms