Influence of Wet–Dry Cycling on the Self‐Assembly and Physicochemical Properties of Model Protocellular Membrane Systems

Abstract

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.

Porphyrin in Prebiotic Catalysis: Ascertaining a Route for the Emergence of Early Metalloporphyrins**

“…Based on the above observations, we set out to investigate the ability of metal ions to coordinate with TPPS and discern if metal‐coordinated TPPS (M‐TPPS) complexes could result under prebiotically plausible terrestrial geothermal conditions. In addition to being widely considered as a niche pertinent to discerning the emergence of life on the early Earth, these prebiotic settings have previously been shown to facilitate the formation of biopolymers relevant to extant biochemistry [50–54] . Towards this, aqueous solution containing 0.3 mM metal ions and 0.03 mM (ten times lower than metal ion) TPPS was incubated at 70° C, simulating putative early Earth conditions [55] (details in Experimental Section).…”

“…In addition to being widely considered as a niche pertinent to discerning the emergence of life on the early Earth, these prebiotic settings have previously been shown to facilitate the formation of biopolymers relevant to extant biochemistry. [50][51][52][53][54] Towards this, aqueous solution containing 0.3 mM metal ions and 0.03 mM (ten times lower than metal ion) TPPS was incubated at 70°C, simulating putative early Earth conditions [55] (details in Experimental Section). Metal coordination with the TPPS scaffold was monitored at specific time points using the temporal change observed in the UV absorption spectrum and steady-state fluorescence spectroscopy (Supporting Information Figures S11-22).…”

pH-responsive self-assembled compartments as tuneable model protocellular membrane systems

“…The NR emission intensity ratio of 610 nm to 660 nm (I610/I660) was measured to gauge the micropolarity of the DDP membrane. Higher the ratio, lesser is the water accessibility on the membrane, thereby, indicating a decrease in micropolarity [27,34] . NR I610/I660 was found to be lowest (0.2±0.03) in water as shown in Fig S16b . NR showed an emission maximum at 590 nm upon incorporation in the DDP membrane at pH 4 with the I610/I660 ratio of 2.4±06, indicating the low micropolarity of the membrane (Fig 2a and Fig.…”

“…The NR emission intensity ratio of 610 nm to 660 nm (I 610 /I 660 ) was measured to gauge the micropolarity of the DDP membrane. Higher the ratio, lesser is the water accessibility on the membrane, thereby, indicating a decrease in micropolarity [27,34] . NR I 610 /I 660 was found to be lowest (0.2±0.03) in water as shown in Fig S16b.…”

Increasing complexity of primitive compartments

“…Although the first primitive compartments on Earth may have indeed been membraneless, and many membraneless organelles provide important biological functions within extant cells (suggesting the importance of phase separation throughout evolution) [1,29], at some point in history, a membrane-bound cell-like compartment must have preceded modern cells. Such a membrane-bound protocell could have taken the form of lipid-bound liposomes or vesicles [30][31][32], perhaps initially composed of simpler fatty acids [33,34] with subsequent evolution first into mixed amphiphile membranes [35][36][37] and finally into the phospholipid-containing form reminiscent of modern membranes [38]. As such, mechanisms of membrane assembly, dynamics, and evolution are key to understanding the emergence of primitive membranes.…”