protocellular membranes are thought to be composed of mixtures of single chain amphiphiles, such as fatty acids and their derivatives, moieties that would have been part of the complex prebiotic chemical landscape. the composition and physico-chemical properties of these prebiological membranes would have been significantly affected and regulated by their environment. In this study, pertinent properties were systematically characterized, under early Earth conditions. Two different fatty acids were mixed with their respective alcohol and/or glycerol monoester derivatives to generate combinations of binary and tertiary membrane systems. their properties were then evaluated as a function of multiple factors including their stability under varying pH, varying Mg 2+ ion concentrations, dilution regimes, and their permeability to calcein. our results demonstrate how environmental constraints would have acted as important prebiotic selection pressures to shape the evolution of prebiological membranes. the study also illustrates that compositionally diverse membrane systems are more stable and robust to multiple selection pressures, thereby making them more suitable for supporting protocellular life. The earliest forms of cellular life are considered to be entities that comprised of dynamic chemical reactions, encapsulated within amphiphilic compartments 1,2. Unlike the contemporary biological membranes model protocellular membranes are thought to have been relatively simpler and composed of single chain amphiphiles (SCAs) 3. These SCAs could have come about on the early Earth either by endogenous synthesis, in the form of Fisher-Tropsch Type (FTT) reactions, or via exogenous delivery 4,5. In this context, fatty acids and their derivatives have been predominantly studied for their plausible role as early compartments 3,6. Fatty acids are known to possess high critical vesicular concentrations (CVCs), the concentration at which the monomers assemble into higher ordered structures like vesicles 7. Such high CVC requirement poses significant obstacles towards their self-assembly under prebiotic scenarios, wherein meeting this high concentration prerequisite would have been difficult 8,9. The pH of certain terrestrial hydrothermal pools of the early Earth is hypothesized to be neutral to alkaline 10 which can drive prebiotically pertinent reactions, including formose reaction 11 , polymerization of non-activated amino acids 12 , and non-canonical nucleoside or nucleotide formation 13. However fatty acid monomers can assemble only in a narrow pH regime, near to their pKa 6,14. Given this scenario the coexistence of the aforementioned reactions and model protocellular membranes would have been really challenging. Moreover, fatty acids are also cation sensitive moieties 15. On the contrary, RNA molecules, which are thought to be the first biomolecules to have emerged, require divalent cations in order to efficiently replicate and carry out catalytic functions 16-18. Such divalent cation concentrations are not compatible with fa...

Wet‐dry cycles are hypothesized to facilitate fundamental steps towards the emergence of life on prebiotic Earth. Multiple wet–dry cycles have been demonstrated to promote biopolymer formation. However, the effect of recurring wet‐dry cycles on the self‐assembly and physicochemical properties of model protocellular membranes remains somewhat obscure. Towards this end, we evaluated the structural and chemical stability of composite model protocell membrane systems composed of single chain amphiphiles, under wet‐dry cycles. The change in membrane properties, size and encapsulation was also investigated. Model protocellular membrane systems were found to reassemble into vesicles even over multiple cycling. Wet‐dry cycling induced compositional changes in the membranes, leading to changes in their physicochemical properties. Multiple cycles were also found to increase vesicular encapsulation of calcein. This work outlines how wet‐dry cycling on the early Earth could have helped in the formation of protocellular entities and their evolution on prebiotic Earth.

No abstract

The front cover artwork is provided by the Rajamani group at IISER Pune. The image depicts the self‐assembly and encapsulation of model protocell membranes under prebiotically pertinent wet–dry cycles. Read the full text of the Article at 10.1002/syst.202100014.

The spontaneous emergence of long RNA molecules on the early Earth, a phenomenon central to the RNA World hypothesis, continues to remain an enigma in the field of origins of life. Few studies have looked at the nonenzymatic oligomerization of cyclic mononucleotides under neutral to alkaline conditions, albeit in fully dehydrated state. In this study, we systematically investigated the oligomerization of cyclic nucleotides under prebiotically relevant conditions, wherein starting reactants were subjected to repeated dehydration-rehydration (DH-RH) regimes. DH-RH conditions, a recurring geological theme that was prevalent on prebiotic Earth, are driven by naturally occurring processes including diurnal cycles and tidal pool activity. These conditions have been shown to facilitate uphill oligomerization reactions. The polymerization of 2 ′ ′ ′ ′ ′ -3 ′ ′ ′ ′ ′ and 3 ′ ′ ′ ′ ′ -5 ′ ′ ′ ′ ′ cyclic nucleotides of a purine (adenosine) and a pyrimidine (cytidine) was investigated. Additionally, the effect of amphiphiles was also evaluated. Furthermore, to discern the effect of "realistic" conditions on this process, the reactions were also performed using a hot spring water sample from a candidate early Earth environment. Our study showed that the oligomerization of cyclic nucleotides under DH-RH conditions resulted in intact informational oligomers. Amphiphiles increased the stability of both the starting monomers and the resultant oligomers in selected reactions. In the hot spring reactions, both the oligomerization of nucleotides and the back hydrolysis of the resultant oligomers were pronounced. Altogether, this study demonstrates how nonenzymatic oligomerization of cyclic nucleotides, under both laboratory-simulated prebiotic conditions and in a candidate early Earth environment, could have resulted in RNA oligomers of a putative RNA World.

The spontaneous emergence of RNA on the early Earth continues to remain an enigma in the field of origins of life. Few studies have looked at the nonenzymatic oligomerization of cyclic nucleotides under neutral to alkaline conditions, in fully dehydrated state. Herein, we systematically investigated the oligomerization of cyclic nucleotides under prebiotically relevant conditions, where starting reactants were subjected to repeated dehydration-rehydration (DH-RH) regimes, like they would have been on an early Earth. DH-RH conditions, a recurring geological theme, are driven by naturally occurring processes including diurnal cycles and tidal pool activity. These conditions have been shown to facilitate uphill oligomerization reactions in terrestrial geothermal niches, which are hypothesized to be pertinent sites for the emergence of life. 2′-3′ and 3′-5′ cyclic nucleotides of one purine-based (adenosine) and one pyrimidine-based (cytidine) system were evaluated in this study. Additionally, the effect of amphiphiles was also investigated. Furthermore, to discern the effect of 'realistic' conditions on this process, the reactions were also performed using hot spring water samples from an early Earth analogue environment. Our results showed that the oligomerization of cyclic nucleotides under DH-RH conditions resulted in intact informational oligomers. Amphiphiles increased the stability of, both, the starting monomers and the resultant oligomers. In analogue condition reactions, oligomerization of nucleotides and back-hydrolysis of the resultant oligomers was pronounced.Altogether, this study demonstrates how nonenzymatic oligomerization of cyclic purine and pyrimidine nucleotides, under laboratory-simulated and early Earth analogous conditions, could have resulted in RNA oligomers of a putative RNA World.Dagar, S.

No abstract

Metal ions are known to catalyze certain prebiotic reactions. However, the transition from metal ions to extant metalloenzymes remains unclear. Porphyrins are found ubiquitously in the catalytic core of many ancient metalloenzymes. In this study, we evaluated the influence of porphyrin-based organic scaffold, on the catalysis, emergence and putative molecular evolution of prebiotic metalloporphyrins. We studied the effect of porphyrins on the transition metal ion-mediated oxidation of hydroquinone (HQ). We report a change in the catalytic activity of the metal ions in the presence of porphyrin. This was observed to be facilitated by the coordination between metal ions and porphyrins or by the formation of non-coordinated complexes. The metal-porphyrin complexes also oxidized NADH, underscoring its versatility at oxidizing more than one substrate. Our study highlights the selective advantage that some of the metal ions would have had in the presence of porphyrin, underscoring their role in shaping the evolution of protometalloenzymes.