Subcompartmentalization and pseudo-division of model protocells

Abstract

Membrane enclosed intracellular compartments have been exclusively associated with the eukaryotes, represented by the highly compartmentalized last eukaryotic common ancestor. Recent evidence showing the presence of membranous compartments with specific functions in archaea and bacteria makes it conceivable that the last universal common ancestor and its hypothetical precursor, the protocell, could have exhibited compartmentalization. To our knowledge, there are no experimental studies yet that have tested this hypothesis. We report on an autonomous subcompartmentalization mechanism for protocells which results in the transformation of initial subcompartments to daughter protocells. The process is solely determined by the fundamental materials properties and interfacial events, and do not require biological machinery or chemical energy supply. In the light of our findings, we propose that similar events could have taken place under early Earth conditions, leading to the development of compartmentalized cells and potentially, primitive division.The origin of the eukaryotic cell is closely associated with the development of subcompartments, which create specific micro-environments to spatially or temporally regulate biochemical reactions, simultaneously. Until recently, cellular compartmentalization was associated solely with eukaryotic systems. Recent evidence shows that membrane-enclosed compartments also exist in other domains of life, such as in Archaea and Bacteria 1,2 . Archaea, for example, have acidocalcisomes, the membrane enclosed electron-dense granular organelles rich in calcium and phosphate, which is crucial for osmoregulation and calcium homeostasis 3 . In Cyanobacteria, membrane-bound thylakoids 4 , have been identified as compartments in which the light-dependent reactions of photosynthesis take place.Despite the differences between eukaryotic and prokaryotic compartments in terms of structural and functional complexity, the presence of membranous compartments in Procaryota 1 establishes a possibility of compartments having existed in protocells, and being evolutionarily conserved. There is essentially no experimental material, however, on how compartments could have consistently emerged from membranes in a prebiotic environment lacking membrane-shaping and -stabilizing proteins.Membrane-less laboratory models of cytoplasmic suborganization have been developed inside synthetic cells, i.e. giant unilamellar vesicles 5 . These models require moderately elaborate chemical systems. A few examples of the utilized materials and mechanisms to induce compartment formation involve thermo-responsive hydrogels 6 , pH driven protein (human serum albumin) localization 7 or a poly(ethylene glycol)-dextran aqueous two-phase system 8 . One study which report on the membrane-based multi-vesiculation inside amphiphilic compartments, has employed protein-ligand couples to induce this behavior, i.e. biotin-avidin conjugates 9 . Membrane-enveloped subcompartment formation in biological systems is therefore considered t...

Liposome-assisted in-situ cargo delivery to artificial cells and cellular subcompartments

“…4i , the xz cross-sectional view at 21 min. Unlike subcompartment #2, #1 appears to be completely sealed or connected to the basal membrane through a nano-sized tether, which would not be visible in the micrograph 4 ( Fig. 4i-j) .…”

“…4d ). We recently reported the unusual compartment formation on the base of surface-adhered GUVs 4 , which could be, in the context of the origins of life, a conceivable way of division and generation of functional diversity within primitive containers. After enzyme delivery to the GUV, the subcompartmentalized vesicle was exposed to the substrate ( Fig.…”

“…4g ), indicating that most of the substrate (CFDA) leaked out before it could be converted to the product (CF). Since the subcompartmentalization is a result of tension-driven membrane flow from areas of high to areas of low membrane curvature, we anticipate that more transient pores 4, 56 open in this particular compartment, which is the likely the cause of leakage of the substrate. Disappearance of small vesicles at the protocell membrane (red arrows in Fig.…”

“…Since the enzyme-encapsulating liposome suspension was not purified (e.g. by dialysis, gel filtration or centrifugation), free enzyme from the surrounding solution can be internalized through the gap between the surface and the basal membrane 4 . Alternatively, active transport via Marangoni flow can transport membrane-adsorbed free cargo (e.g.…”

“…Alternatively, active transport via Marangoni flow can transport membrane-adsorbed free cargo (e.g. enzyme) to the subcompartments 4, 57 . In this case, we can assume that all subcompartments should have a similar amount of enzyme internalized.…”