Explore the vast range of titles available.

Key requirements for the first cells on Earth include the ability to compartmentalize and evolve. Compartmentalization spatially localizes biomolecules from a dilute pool and an evolving cell, which, as it grows and divides, permits mixing and propagation of information to daughter cells. Complex coacervate microdroplets are excellent candidates as primordial cells with the ability to partition and concentrate molecules into their core and support primitive and complex biochemical reactions. However, the evolution of coacervate protocells by fusion, growth and fission has not yet been demonstrated. In this work, a primordial environment initiated the evolution of coacervate-based protocells. Gas bubbles inside heated rock pores perturb the coacervate protocell distribution and drive the growth, fusion, division and selection of coacervate microdroplets. Our findings provide a compelling scenario for the evolution of membrane-free coacervate microdroplets on the early Earth, induced by common gas bubbles within heated rock pores. Complex coacervate microdroplets have been proposed as primordial cells, but their ability to evolve by fusion, growth and fission has not yet been demonstrated. Now, it has been shown that gas bubbles inside heated rock pores can drive the growth, fusion, division and selection of coacervate microdroplets.

It has long been proposed that phase-separated compartments can provide a basis for the formation of cellular precursors in prebiotic environments. However, we know very little about the properties of coacervates formed from simple peptides, their compatibility with ribozymes or their functional significance. Here we assess the conditions under which functional ribozymes form coacervates with simple peptides. We find coacervation to be most robust when transitioning from long homopeptides to shorter, more pre-biologically plausible heteropeptides. We mechanistically show that these RNA–peptide coacervates display peptide-dependent material properties and cofactor concentrations. We find that the interspacing of cationic and neutral amino acids increases RNA mobility, and we use isothermal calorimetry to reveal sequence-dependent Mg 2+ partitioning, two critical factors that together enable ribozyme activity. Our results establish how peptides of limited length, homogeneity and charge density facilitate the compartmentalization of active ribozymes into non-gelating, magnesium-rich coacervates, a scenario that could be applicable to cellular precursors with peptide-dependent functional phenotypes. Phase-separated compartments have long been proposed as precursors to cellular life. Now, it has been shown that RNA–peptide protocells are more robust when formed using shorter (rather than longer) peptides, and that peptide sequence determines the functional materials properties of these compartments.

Mechanisms of prebiotic compartmentalization are central to providing insights into how protocellular systems emerged on the early Earth. Protocell models are based predominantly on the membrane self-assembly of fatty-acid vesicles, although membrane-free scenarios that involve liquid–liquid microphase separation (coacervation) have also been considered. Here we integrate these alternative models of prebiotic compartmentalization and develop a hybrid protocell model based on the spontaneous self-assembly of a continuous fatty-acid membrane at the surface of preformed coacervate microdroplets prepared from cationic peptides/polyelectrolytes and adenosine triphosphate or oligo/polyribonucleotides. We show that the coacervate-supported membrane is multilamellar, and mediates the selective uptake or exclusion of small and large molecules. The coacervate interior can be disassembled without loss of membrane integrity, and fusion and growth of the hybrid protocells can be induced under conditions of high ionic strength. Our results highlight how notions of membrane-mediated compartmentalization, chemical enrichment and internalized structuration can be integrated in protocell models via simple chemical and physical processes. A hybrid protocell model is described in which a fatty acid membrane spontaneously assembles on the surface of coacervate microdroplets with molecularly crowded interiors. The membrane-enclosed protocells exhibit uptake and exclusion properties that differ from the uncoated droplets. The internal structure can be disassembled at high ionic strength without loss of membrane integrity. This model may help to reconcile alternative mechanisms of prebiotic compartmentalization.

Membrane-free complex coacervate microdroplets are compelling models for primitive compartmentalisation with the ability to form from biological molecules. However, understanding how molecular interactions can influence physicochemical properties and catalytic activity of membrane-free compartments is still in its infancy. This is important for defining the function of membrane-free compartments during the origin of life as well as in modern biology. Here, we use RNA-peptide coacervate microdroplets prepared with prebiotically relevant amino acids and a minimal hammerhead ribozyme. This is a model system to probe the relationship between coacervate composition, its properties and ribozyme activity. We show that ribozyme catalytic activity is inhibited within the coacervate compared to buffer solution, whilst variations in peptide sequence can modulate rates and yield of the ribozyme within the coacervate droplet by up to 15-fold. The apparent ribozyme rate constant is anti-correlated with its concentration and correlated to its diffusion coefficient within the coacervates. Our results provide a relationship between the physicochemical properties of the coacervate microenvironment and the catalytic activity of the ribozyme where membrane-free compartments could provide a selection pressure to drive molecular evolution on prebiotic earth. Membrane-free complex coacervate microdroplets are compelling models for primitive compartmentalization, but it is unclear how molecular co-operativity influences physicochemical properties and activity of membrane-free compartments. Here, the authors use RNA/peptide coacervates as a model to reveal the relationship between coacervate properties and ribozyme activity.

Condensates formed by complex coacervation are hypothesized to have played a crucial part during the origin-of-life. In living cells, condensation organizes biomolecules into a wide range of membraneless compartments. Although RNA is a key component of biological condensates and the central component of the RNA world hypothesis, little is known about what determines RNA accumulation in condensates and to which extend single condensates differ in their RNA composition. To address this, we developed an approach to read the RNA content from single synthetic and protein-based condensates using high-throughput sequencing. We find that certain RNAs efficiently accumulate in condensates. These RNAs are strongly enriched in sequence motifs which show high sequence similarity to short interspersed elements (SINEs). We observe similar results for protein-derived condensates, demonstrating applicability across different in vitro reconstituted membraneless organelles. Thus, our results provide a new inroad to explore the RNA content of phase-separated droplets at single condensate resolution. Here, the authors demonstrate that single cell RNA sequencing technology can be leveraged to characterize RNA content of individual membrane-free condensates formed by liquid-liquid phase separation processes such as coacervation.

Condensed coacervate phases are now understood to be important features of modern cell biology, as well as valuable protocellular models in origin-of-life studies and synthetic biology. In each of these fields, the development of model systems with varied and tuneable material properties is of great importance for replicating properties of life. Here, we develop a ligase ribozyme system capable of concatenating short RNA fragments into long chains. Our results show that the formation of coacervate microdroplets with the ligase ribozyme and poly(L-lysine) enhances ribozyme rate and yield, which in turn increases the length of the anionic polymer component of the system and imparts specific physical properties to the droplets. Droplets containing active ribozyme sequences resist growth, do not wet or spread on unpassivated surfaces, and exhibit reduced transfer of RNA between droplets when compared to controls containing inactive sequences. These altered behaviours, which stem from RNA sequence and catalytic activity, constitute a specific phenotype and potential fitness advantage, opening the door to selection and evolution experiments based on a genotype–phenotype linkage.

Phase separation of mixtures of oppositely charged polymers provides a simple and direct route to compartmentalisation via complex coacervation, which may have been important for driving primitive reactions as part of the RNA world hypothesis. However, to date, RNA catalysis has not been reconciled with coacervation. Here we demonstrate that RNA catalysis is viable within coacervate microdroplets and further show that these membrane-free droplets can selectively retain longer length RNAs while permitting transfer of lower molecular weight oligonucleotides. Phase separation of mixtures of oppositely charged polymers provides a simple and direct route to compartmentalisation via coacervation. Here authors demonstrate that a coacervate microenvironment supports RNA catalysis whilst selectively sequestering RNA based on length.

Biomolecular condensation of macromolecules is an increasingly important concept in cell biology. Indeed, research on condensates touches on multiple areas of research, from biochemistry to biophysics and from organelles to cell polarity. We asked experts at the forefront of this field to comment on what excites them most regarding biomolecular condensation, as well as on current challenges, priorities and needs for the functional study of condensates.

Coupled compartmentalised information processing and communication via molecular diffusion underpin network based population dynamics as observed in biological systems. Understanding how both compartmentalisation and communication can regulate information processes is key to rational design and control of compartmentalised reaction networks. Here, we integrate PEN DNA reactions into semi-permeable proteinosomes and characterise the effect of compartmentalisation on autocatalytic PEN DNA reactions. We observe unique behaviours in the compartmentalised systems which are not accessible under bulk conditions; for example, rates of reaction increase by an order of magnitude and reaction kinetics are more readily tuneable by enzyme concentrations in proteinosomes compared to buffer solution. We exploit these properties to regulate the reaction kinetics in two node compartmentalised reaction networks comprised of linear and autocatalytic reactions which we establish by bottom-up synthetic biology approaches. Our understanding of how compartmentalisation and intercellular communication can tune enzyme reactions is still in its infancy. Here, the authors show that multi-enzyme reactions within semi-permeable compartments have distinct properties compared to reactions in buffer solution.

Many complex behaviors in biological systems emerge from large populations of interacting molecules or cells, generating functions that go beyond the capabilities of the individual parts. Such collective phenomena are of great interest to bioengineers due to their robustness and scalability. However, engineering emergent collective functions is difficult because they arise as a consequence of complex multi-level feedback, which often spans many length-scales. Here, we present a perspective on how some of these challenges could be overcome by using multi-agent modeling as a design framework within synthetic biology. Using case studies covering the construction of synthetic ecologies to biological computation and synthetic cellularity, we show how multi-agent modeling can capture the core features of complex multi-scale systems and provide novel insights into the underlying mechanisms which guide emergent functionalities across scales. The ability to unravel design rules underpinning these behaviors offers a means to take synthetic biology beyond single molecules or cells and toward the creation of systems with functions that can only emerge from collectives at multiple scales.