Physical Principles and Extant Biology Reveal Roles for RNA-Containing Membraneless Compartments in Origins of Life Chemistry

Abstract

This Perspective focuses on RNA in biological and nonbiological compartments resulting from liquid-liquid phase separation (LLPS), with an emphasis on origins of life. In extant cells, intracellular liquid condensates, many of which are rich in RNAs and intrinsically disordered proteins, provide spatial regulation of biomolecular interactions that can result in altered gene expression. Given the diversity of biogenic and abiogenic molecules that undergo LLPS, such membraneless compartments may have also played key roles in prebiotic chemistries relevant to the origins of life. The RNA World hypothesis posits that RNA may have served as both a genetic information carrier and a catalyst during the origin of life. Because of its polyanionic backbone, RNA can undergo LLPS by complex coacervation in the presence of polycations. Phase separation could provide a mechanism for concentrating monomers for RNA synthesis and selectively partition longer RNAs with enzymatic functions, thus driving prebiotic evolution. We introduce several types of LLPS that could lead to compartmentalization and discuss potential roles in template-mediated non-enzymatic polymerization of RNA and other related biomolecules, functions of ribozymes and aptamers, and benefits or penalties imparted by liquid demixing. We conclude that tiny liquid droplets may have concentrated precious biomolecules and acted as bioreactors in the RNA World.

Temperature, Hydrostatic Pressure, and Osmolyte Effects on Liquid–Liquid Phase Separation in Protein Condensates: Physical Chemistry and Biological Implications

“…Intriguingly,a sf irst proposed in the seminalw ork of Oparin in 1924 [28,29] and emphasized recently, [30] biomolecularL LPS and membrane-lessc ompartmentalization might even have played an importantr ole in the development of protocells in prebiotice volution. [31,[39][40][41] As far as temperature dependence of LLPS is concerned, some proteins, such as folded egg-white lysozyme [42] and the N-terminal IDR of DEAD-Box helicase Ddx4, [21] were found to exhibit an upper criticals olution temperature (UCST), i.e.,L LPS occurs only at temperatures below ac ritical temperature T c , whereas the system is homogeneous at highert emperatures. Other proteins, such as the polyA-binding protein (Pab) [43] and the IDP a-elastin, [44] exhibit al ower criticals olution temperature (LCST) in that LLPS occurs at temperatures higher than T c and the system is homogeneous at lower temperatures ( Figure 1).…”

Cell‐Inspired All‐Aqueous Microfluidics: From Intracellular Liquid–Liquid Phase Separation toward Advanced Biomaterials

“…This approach can be adaptable for enzyme‐catalyzed synthesis of a wide variety of materials, by varying the type of metal ion and enzyme. Moreover, Benefiting from the preferential partitioning of the all‐aqueous emulsions, the templated architectures can be applied as bioreactors for mimicking intracellular biological reactions within living cells . For instance, these bioreactors can be utilized to perform enzymatic reactions between the glucose oxidase (GOX) and horseradish peroxidase (HRP) in the PEG/citrate ATPS as shown in Figure 23c,d .…”

Prebiotically-relevant low polyion multivalency can improve functionality of membraneless compartments

“…Salt dependence of coacervate formation: Ion pairing-based phase separation is strongly dependent on solution ionic strength, with critical salt concentrations above which coacervates dissolve dependent upon multivalency. 19,22,27 We evaluated the salt stability of coacervates formed using primarily n=10 cationic peptides with anions that included nucleotides and both 9 carboxylate oligopeptides ( Fig. 3A-D, Supplementary Table 1).…”

“…7,8 The ion pairing interactions between coacervate-forming polymers are nonspecific and hence versatile and achievable with a wide range of biological and nonbiological chemistries. 7,[9][10][11][12] Biomolecules such as RNAs can be concentrated within coacervates to orders of magnitude higher than in the external milieu. 9,13 These higher local concentrations can provide rate enhancements for catalytic RNAs encapsulated within coacervate droplets.…”

“…7,[9][10][11][12] Biomolecules such as RNAs can be concentrated within coacervates to orders of magnitude higher than in the external milieu. 9,13 These higher local concentrations can provide rate enhancements for catalytic RNAs encapsulated within coacervate droplets. 5,14,15 Coacervates also provide a distinct microenvironment that can differ from the dilute phase in terms of solvent polarity, 16,17 concentrations of metal ions such as Mg 2+ , 13 or the presence of cofactors such as spermine, which can enhance ribozyme function.…”