Liposome membrane itself can affect gene expression in the Escherichia coli cell-free translation system

Efficiency of transcription and translation of cell-free protein synthesis systems in cell-sized lipid vesicles with changing lipid composition determined by fluorescence measurements

To develop artificial cell models that mimic living cells, cell-sized lipid vesicles encapsulating cell-free protein synthesis (CFPS) systems are useful for protein expressions or artificial gene circuits for vesicle-vesicle communications. Therefore, investigating the transcriptional and translational properties of CFPS systems in lipid vesicles is important for maximizing the synthesis and functions of proteins. Although transcription and translation using CFPS systems inside lipid vesicles are more important than that outside lipid vesicles, the former processes are not investigated by changing the lipid composition of lipid vesicles. Herein, we investigated changes in transcription and translation using CFPS systems inside giant lipid vesicles (approximately 5-20 μm in diameter) caused by changing the lipid composition of lipid vesicles containing neutral, positively, and negatively charged lipids. After incubating for 30 min, 1 h, 2 h, and 4 h, the transcriptional and translational activities in these lipid vesicles were determined by detecting the fluorescence intensities of the fluorogenic RNA aptamer on the 3'-untranslated region of mRNA (transcription) and the fluorescent protein sfCherry (translation), respectively. The results revealed that transcriptional and translational activities in a lipid vesicle containing positively charged lipids were high when the protein was synthesized using the CFPS system inside the lipid vesicle. Thus, the present study provides an experimental basis for constructing complex artificial cell models using bottom-up approaches.

Geometric Effect for Biological Reactors and Biological Fluids

As expressed "God made the bulk; the surface was invented by the devil" by W. Pauli, the surface has remarkable properties because broken symmetry in surface alters the material properties. In biological systems, the smallest functional and structural unit, which has a functional bulk space enclosed by a thin interface, is a cell. Cells contain inner cytosolic soup in which genetic information stored in DNA can be expressed through transcription (TX) and translation (TL). The exploration of cell-sized confinement has been recently investigated by using micron-scale droplets and microfluidic devices. In the first part of this review article, we describe recent developments of cell-free bioreactors where bacterial TX-TL machinery and DNA are encapsulated in these cell-sized compartments. Since synthetic biology and microfluidics meet toward the bottom-up assembly of cell-free bioreactors, the interplay between cellular geometry and TX-TL advances better control of biological structure and dynamics in vitro system. Furthermore, biological systems that show self-organization in confined space are not limited to a single cell, but are also involved in the collective behavior of motile cells, named active matter. In the second part, we describe recent studies where collectively ordered patterns of active matter, from bacterial suspensions to active cytoskeleton, are self-organized. Since geometry and topology are vital concepts to understand the ordered phase of active matter, a microfluidic device with designed compartments allows one to explore geometric principles behind self-organization across the molecular scale to cellular scale. Finally, we discuss the future perspectives of a microfluidic approach to explore the further understanding of biological systems from geometric and topological aspects.

Extrinsic stochastic factors (solute partition) in gene expression inside lipid vesicles and lipid-stabilized water-in-oil droplets: a review

The encapsulation of transcription-translation (TX-TL) machinery inside lipid vesicles and water-in-oil droplets leads to the construction of cytomimetic systems (often called 'synthetic cells') for synthetic biology and origins-of-life research. A number of recent reports have shown that protein synthesis inside these microcompartments is highly diverse in terms of rate and amount of synthesized protein. Here, we discuss the role of extrinsic stochastic effects (i.e. solute partition phenomena) as relevant factors contributing to this pattern. We evidence and discuss cases where between-compartment diversity seems to exceed the expected theoretical values. The need of accurate determination of solute content inside individual vesicles or droplets is emphasized, aiming at validating or rejecting the predictions calculated from the standard fluctuations theory. At the same time, we promote the integration of experiments and stochastic modeling to reveal the details of solute encapsulation and intra-compartment reactions.

Roles of Sterol Derivatives in Regulating the Properties of Phospholipid Bilayer Systems

Liposomes are considered an ideal biomimetic environment and are potential functional carriers for important molecules such as steroids and sterols. With respect to the regulation of self-assembly via sterol insertion, several pathways such as the sterol biosynthesis pathway are affected by the physicochemical properties of the membranes. However, the behavior of steroid or sterol molecules (except cholesterol (Chl)) in the self-assembled membranes has not been thoroughly investigated. In this study, to analyze the fundamental behavior of steroid molecules in fluid membranes, Chl, lanosterol, and ergosterol were used as representative sterols in order to clarify how they regulate the physicochemical properties of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes. Membrane properties such as surface membrane fluidity, hydrophobicity, surface membrane polarity, inner membrane polarity, and inner membrane fluidity were investigated using fluorescent probes, including 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene, 8-anilino-1-naphthalenesulfonic acid, 6-propionyl-2-(dimethylamino) naphthalene, 6-dodecanoyl-2-dimethylaminonaphthalene, and 1,6-diphenyl-1,3,5-hexatriene. The results indicated that each sterol derivative could regulate the membrane properties in different ways. Specifically, Chl successfully increased the packing of the DOPC/Chl membrane proportional to its concentration, and lanosterol and ergosterol showed lower efficiencies in ordering the membrane in hydrophobic regions. Given the different binding positions of the probes in the membranes, the differences in membrane properties reflected the relationship between sterol derivatives and their locations in the membrane.

Quantitative Monitoring of Microphase Separation Behaviors in Cationic Liposomes Using HHC, DPH, and Laurdan: Estimation of the Local Electrostatic Potentials in Microdomains

Microphase separation behaviors of cationic liposomes have been investigated using a pH-sensitive fluorescent probe with 4-heptadecyl-7-hydroxycoumarin (HHC), 1,6-diphenyl-1,3,5-hexatriene, and 6-lauroyl-2-dimethylaminonaphthalene, and to estimate localized electrostatic potentials. Shifts of the apparent pKa values of HHC were observed in cationic liposomes in proportion to the amount of cationic lipids. Two pKa values were obtained with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/3β-[N(N',N'-dimethylaminoethane)-carbamoyl] cholesterol hydrochloride (DC-Ch) liposomes, while only one pKa value was generated with either DOPC/1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or DOPC/dimethyldioctadecylammonium-bromide (DODAB) liposomes. The physicochemical membrane property analyses, focusing on membrane fluidity and membrane polarity, revealed heterogeneity among DOPC/DC-Ch liposomes. By analyzing the pH titration curves using sigmoidal fitting, the localized electrostatic potentials were estimated. For DOPC/DOTAP = (7/3), the membrane was in the liquid-disordered phase and the density of cationic molecules was 0.41 cation/nm(2). For DOPC/DC-Ch = (7/3), the membrane was heterogeneous and the densities of cationic molecules in liquid-disordered and liquid-ordered phases were 0.25 and 1.24 cation/nm(2), respectively. We thereby conclude that the DC-Ch molecules can form nanodomains when these molecules are concentrated to 59%.

Liposomes modified with cardiolipin can act as a platform to regulate the potential flux of NADP+-dependent isocitrate dehydrogenase

Cardiolipin (CL) is a phospholipid found in the outer mitochondrial membrane (OMM) and inner mitochondrial membrane (IMM) in animal cells. Isocitrate dehydrogenase (ICDH) is an important catalytic enzyme that is localized at the cytosol and mitochondria; the metabolic pathway catalyzed by ICDH differs between the OMM and IMM. To estimate the possible role of lipid membrane in the enzymatic activity of NADP⁺-dependent ICDH, CL-modified liposomes were prepared using CL/1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/cholesterol (Ch), and their characteristics were analyzed based on the fluorescent probe method. The relative enzymatic activity of ICDH decreased in the presence of CL/DPPC/Ch=(30/50/20) liposome, whereas activity increased in the presence of CL/DPPC/Ch=(5/75/20) liposome. NADP⁺ had the greatest substrate affinity and was dominant in the regulation of ICDH activity. Analysis of membrane properties indicated that membranes in CL-modified liposomes were dehydrated by ICDH binding. Using circular dichroism analysis, CL/DPPC/Ch=(30/50/20) liposome induced a conformational change in ICDH, indicating that CL-rich membrane domains could inhibit ICDH activity. These results suggest that lipid membranes, including CL molecules, could act as a platform to regulate ICDH-related metabolic pathways such as the tricarboxylic acid cycle and lipid synthesis.

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Phosphatidylcholine liposomes were modified with cardiolipin and characterized.

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DPPC liposomes did not affect the activity of ICDH.

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ICDH activity was enhanced with liposomes at 5 mol% cardiolipin.

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ICDH activity was lowered with liposomes at 30 mol% cardiolipin.

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Liposomes with high content of cardiolipin led to conformational changes of ICDH.

Pyrrhocoricin, a proline-rich antimicrobial peptide derived from insect, inhibits the translation process in the cell-free Escherichia coli protein synthesis system

Previous studies have shown that pyrrhocoricin, a proline-rich antimicrobial peptide (PrAMP), killed sensitive species in a dose-dependent manner by specifically binding to DnaK. Here, on the basis of the finding that DnaK-deficient Escherichia coli strains are susceptible to PrAMPs, we used pyrrhocoricin to investigate internal targets other than DnaK. Using conventional antibiotics (bleomycin, streptomycin, and fosfomycin) that have known modes of action, first, we validated the availability of an assay using a cell-free rapid translation system (RTS), which is an in vitro protein synthesis system based on E. coli lysate, for evaluating inhibition of protein synthesis. We found that, similarly to bleomycin and streptomycin, pyrrhocoricin inhibited GFP synthesis in RTS in a concentration-dependent manner. In addition, blockage of transcription and translation steps in RTS was individually estimated using RT-PCR after gene expression to determine mRNA products and using sodium dodecyl sulfate-polyacrylamide gel electrophoresis to determine the amounts of GFP expressed from purified mRNA, respectively. The results demonstrated that this inhibition of GFP synthesis by pyrrhocoricin did not occur at the transcription step but rather at the translation step, in a manner similar to that of GFP synthesis by streptomycin, an inhibitor of the translation step by causing misreading of tRNA. These results suggest that RTS is a powerful assay system for determining if antimicrobial peptides inhibit protein synthesis and its transcription and/or translation steps. This is the first study to have shown that pyrrhocoricin inhibited protein synthesis by specifically repressing the translation step.

Pseudo-Interphase of Liposome Promotes 1,3-Dipolar Cycloaddition Reaction of Benzonitrile Oxide and N-Ethylmaleimide in Aqueous Solution

The hydrophobic interior of a liposome membrane was used as a platform for the organic synthesis of hydrophobic compounds in water. The 1,3-dipolar cycloaddition of benzonitrile oxide (BNO) and N-ethylmaleimide (EMI) in liposome suspensions was carried out, and an increase in the reaction rate constant was observed depending on the liposome characteristics. While the reaction rate constant in 1,4-dioxane was 1.5 times higher than that in water, the reaction rate constant in an aqueous solution of cationic 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) liposome was 3 times higher than in water. The amount of substrate, BNO, accumulated in the DOTAP liposome was higher than that in 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP), indicating that BNO prefers to be distributed in the liposome membrane in the liquid-disordered phase. The membrane polarity, GP340, as monitored by Laurdan, varied with the presence of BNO, while EMI slightly affected the membrane properties of the liposomes. These results suggest that the pseudo-interphase afforded by the liposome membrane can promote the 1,3-dipolar cycloaddition between BNO and EMI in water.

Emergent properties arising from the assembly of amphiphiles. Artificial vesicle membranes as reaction promoters and regulators

This article deals with artificial vesicles and their membranes as reaction promoters and regulators. Among the various molecular assemblies which can form in an aqueous medium from amphiphilic molecules, vesicle systems are unique. Vesicles compartmentalize the aqueous solution in which they exist, independent on whether the vesicles are biological vesicles (existing in living systems) or whether they are artificial vesicles (formed in vitro from natural or synthetic amphiphiles). After the formation of artificial vesicles, their aqueous interior (the endovesicular volume) may become - or may be made - chemically different from the external medium (the exovesicular solution), depending on how the vesicles are prepared. The existence of differences between endo- and exovesicular composition is one of the features on the basis of which biological vesicles contribute to the complex functioning of living organisms. Furthermore, artificial vesicles can be formed from mixtures of amphiphiles in such a way that the vesicle membranes become molecularly, compositionally and organizationally highly complex, similarly to the lipidic matrix of biological membranes. All the various properties of artificial vesicles as membranous compartment systems emerge from molecular assembly as these properties are not present in the individual molecules the system is composed of. One particular emergent property of vesicle membranes is their possible functioning as promoters and regulators of chemical reactions caused by the localization of reaction components, and possibly catalysts, within or on the surface of the membranes. This specific feature is reviewed and highlighted with a few selected examples which range from the promotion of decarboxylation reactions, the selective binding of DNA or RNA to suitable vesicle membranes, and the reactivation of fragmented enzymes to the regulation of the enzymatic synthesis of polymers. Such type of emergent properties of vesicle membranes may have been important for the prebiological evolution of protocells, the hypothetical compartment systems preceding the first cells in those chemical and physico-chemical processes that led to the origin of life.

Synthetic biology outside the cell: linking computational tools to cell-free systems

As mathematical models become more commonly integrated into the study of biology, a common language for describing biological processes is manifesting. Many tools have emerged for the simulation of in vivo synthetic biological systems, with only a few examples of prominent work done on predicting the dynamics of cell-free synthetic systems. At the same time, experimental biologists have begun to study dynamics of in vitro systems encapsulated by amphiphilic molecules, opening the door for the development of a new generation of biomimetic systems. In this review, we explore both in vivo and in vitro models of biochemical networks with a special focus on tools that could be applied to the construction of cell-free expression systems. We believe that quantitative studies of complex cellular mechanisms and pathways in synthetic systems can yield important insights into what makes cells different from conventional chemical systems.

Systematical characterization of phase behaviors and membrane properties of fatty acid/didecyldimethylammonium bromide vesicles

Fatty acids (FAs) are known to form vesicle structures, depending on the surrounding pH conditions. In this study, we prepared vesicles by mixing FAs and a cationic surfactant, and then investigated their physicochemical properties using fluorescence spectroscopy and dielectric dispersion analysis (DDA). The assemblies formed from oleic acid (OA) and linoleic acid (LA) were modified by adding didecyldimethylammonium bromide (DDAB). The phase state of FA/DDAB mixtures was investigated with pH titration curves and turbidity measurements. The trigonal diagram of FA/ionized FA/DDAB was successfully drawn to understand the phase behaviors of FA/DDAB systems. The analysis of fluidities in the interior of the membrane with use of 1,6-diphenyl-1,3,5-hexatriene (DPH) indicated that the membrane fluidities of OA/DDAB and LA/DDAB at pH 8.5 slightly decreased in proportion to the molar ratio of DDAB in FA/DDAB systems. The fluorescent probe 6-lauroyl-2-dimethylamino naphthalene (Laurdan) indicated that the LA vesicle possessed a dehydrated surface, while the OA vesicle surface was hydrated. Modification of LA vesicles with DDAB induced the hydration of membrane surfaces, whereas modification of OA vesicles by DDAB had the opposite effect. DDA analysis indicated that the membrane surfaces were hydrated in the presence of DDAB, suggesting that the surface properties of FA vesicles are tunable by DDAB modification.

The engineering of artificial cellular nanosystems using synthetic biology approaches

Artificial cellular systems are minimal systems that mimic certain properties of natural cells, including signaling pathways, membranes, and metabolic pathways. These artificial cells (or protocells) can be constructed following a synthetic biology approach by assembling biomembranes, synthetic gene circuits, and cell-free expression systems. As artificial cells are built from bottom-up using minimal and a defined number of components, they are more amenable to predictive mathematical modeling and engineered controls when compared with natural cells. Indeed, artificial cells have been implemented as drug delivery machineries and in situ protein expression systems. Furthermore, artificial cells have been used as biomimetic systems to unveil new insights into functions of natural cells, which are otherwise difficult to investigate owing to their inherent complexity. It is our vision that the development of artificial cells would bring forth parallel advancements in synthetic biology, cell-free systems, and in vitro systems biology. For further resources related to this article, please visit the WIREs website. Conflict of interests: The authors declare that they have no competing financial interests.

Detection of nanosized ordered domains in DOPC/DPPC and DOPC/Ch binary lipid mixture systems of large unilamellar vesicles using a TEMPO quenching method

Nanosized ordered domains formed in 1,2-dioleoyl-sn-glycero-3-phosphocholine/1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DOPC/DPPC) and DOPC/cholesterol (Ch) liposomes were characterized using a newly developed (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) quenching method. The membrane fluidity of the DOPC/DPPC liposomes, evaluated by the use of 1,6-diphenyl-1,3,5-hexatriene (DPH), increased significantly above their phase-transition temperature. The fluorescence spectra of 6-lauroyl-2-dimethylamino naphthalene (Laurdan) indicated the formation of an immiscible ordered phase in the DOPC/DPPC (50/50) liposomal membrane at 30 °C. The analysis of the membrane polarity indicated that the surface of the liquid-disordered phase was hydrated whereas that of the ordered phase was dehydrated. DOPC/DPPC and DOPC/Ch (70/30) liposomes exhibited heterogeneous membranes, indicating that nanosized ordered domains formed on the surface of the DOPC/DPPC liposomes. The size of these nanosized ordered domains was estimated using the TEMPO quenching method. Because TEMPO can quench DPH distributed in the disordered phases, the remaining fluorescence from DPH is proportional to the size of the ordered domain. The domain sizes calculated for DOPC/DPPC (50/50), DOPC/DPPC (25/75), DOPC/Ch (70/30), and DOPC/DPPC/Ch (40/40/20) were 13.9, 36.2, 13.2, and 35.5 Å, respectively.

Heterogeneous cationic liposomes modified with 3β-{N-[(N',N'-dimethylamino)ethyl]carbamoyl}cholesterol can induce partial conformational changes in messenger RNA and regulate translation in an Escherichia coli cell-free translation system

The effect of cationic liposomes (CLs) on messenger RNA(mRNA) conformation and translation was studied, focusing on membrane heterogeneity. CLs, composed of 1,2-dioleoyl-sn-glycerol-3-phosphocholine/1,2-dioleoyl-3-timethylammonium propane (DOPC/DOTAP) and DOPC/3β-{N-[(N',N'-dimethylamino)ethyl]carbamoyl}cholesterol (DOPC/DC-Ch), inhibited mRNA translation in an Escherichia coli cell-free translation system. Analysis of the membrane fluidity and polarity indicated a heterogeneous DOPC/DC-Ch (70/30) membrane, while other CLs exhibited homogeneous disordered membranes. mRNA adsorbed onto DOPC/DC-Ch liposomes showed translational activity, while DOPC/DOTAP liposomes inhibited mRNA translation in proportion to its adsorption onto membranes. Dehydration of DOPC/DOTAP (70/30) and DOPC/DC-Ch (70/30) was observed in the presence of mRNA but not in the case of zwitterionic DOPC liposomes, indicating that mRNA binds in regions between the phosphate [-PO(2)(-)-] and carbonyl [-C=O-] moieties of lipids. UV resonance Raman spectroscopy suggests that adenine, cytosine, and guanine interact with DOPC/DOTAP (70/30) and DOPC/DC-Ch (70/30) but not with DOPC. Circular dichroism indicates that DOPC/DOTAP (70/30) extensively denatured the mRNA. In contrast, heterogeneous DOPC/DC-Ch (70/30) induced partial conformational changes but maintained the translational activity of mRNA.

Effects of compartment size on the kinetics of intracompartmental multimeric protein synthesis

The cell contents are encapsulated within a compartment, the volume of which is a fundamental physical parameter that may affect intracompartmental reactions. However, there have been few studies to elucidate whether and how volume changes alone can affect the reaction kinetics. It is difficult to address these questions in vivo, because forced cell volume changes, e.g., by osmotic inflation/deflation, globally alters the internal state. Here, we prepared artificial cell-like compartments with different volumes but with identical constituents, which is not possible with living cells, and synthesized two tetrameric enzymes, β-glucuronidase (GUS) and β-galactosidase (GAL), by cell-free protein synthesis. Tetrameric GUS but not GAL was synthesized more quickly in smaller compartments. The difference between the two was dependent on the rate-limiting step and the reaction order. The observed acceleration mechanism would be applicable to living cells as multimeric protein synthesis in a microcompartment is ubiquitous in vivo.

Cell-free protein synthesis inside giant unilamellar vesicles analyzed by flow cytometry

Lipid vesicles have been used as model cell systems, in which an in-vitro transcription-translation system (IVTT) is encapsulated to carry out intravesicular protein synthesis. Despite a large number of previous studies, a quantitative understanding of how protein synthesis inside the vesicles is affected by the lipid membrane remains elusive. This is mainly because of the heterogeneity in structural properties of the lipid vesicles used in the experiments. We investigated the effects of the phospholipid membrane on green fluorescent protein (GFP) synthesis occurring inside cell-sized giant unilamellar vesicles (GUV), which have a defined quantity of lipids relative to the reaction volume. We first developed a method to distinguish GUV from multilamellar vesicles using flow cytometry (FCM). Using this method, we investigated the time course of GFP synthesis using one of the IVTT, the PURE system, and found that phospholipid in the form of GUV has little effect on GFP synthesis based on three lines of investigation. (1) GFP synthesis inside the GUV was not dependent on the size of GUV (2) or on the fraction of cholesterol or anionic phospholipid constituting the GUV, and (3) GFP synthesis proceeded similarly in GUV and in the test tube. The present results suggest that GUV provides an ideal reaction environment that does not affect the internal biochemical reaction. On the other hand, we also found that internal GFP synthesis is strongly dependent on the chemical composition of the outer solution.

Cell-Sized confinement in microspheres accelerates the reaction of gene expression

Cell-sized water-in-oil droplet covered by a lipid layer was used to understand how lipid membranes affect biochemical systems in living cells. Here, we report a remarkable acceleration of gene expression in a cell-sized water-in-oil droplet entrapping a cell-free translation system to synthesize GFP (green fluorescent protein). The production rate of GFP (V(GFP)) in each droplet remained almost constant at least for on the order of a day, which implies 0(th)-order reaction kinetics. Interestingly, V(GFP) was inversely proportional to radius of droplets (R) when R is under 50 μm, and V(GFP) in droplets with R ∼ 10 μm was more than 10 times higher than that in the bulk. The acceleration rates of GFP production in cell-sized droplets strongly depended on the lipid types. These results demonstrate that the membrane surface has the significant effect to facilitate protein production, especially when the scale of confinement is on the order of cell-size.

Programmed vesicle fusion triggers gene expression

The membrane properties of phospholipid vesicles can be manipulated to both regulate and initiate encapsulated biochemical reactions and networks. We present evidence for the inhibition and activation of reactions encapsulated in vesicles by the exogenous addition of charged amphiphiles. While the incorporation of cationic amphiphile exerts an inhibitory effect, complementation of additional anionic amphiphiles revitalize the reaction. We demonstrated both the simple hydrolysis reaction of β-glucuronidase and the in vitro gene expression of this enzyme from a DNA template. Furthermore, we show that two vesicle populations decorated separately with positive and negative amphiphiles can fuse selectively to supply feeding components to initiate encapsulated reactions. This mechanism could be one of the rudimentary but effective means to regulate and maintain metabolism in dynamic artificial cell models.

Conformational change of single-stranded RNAs induced by liposome binding

The interaction between single-stranded RNAs and liposomes was studied using UV, Fourier Transform Infrared spectroscopy (FTIR) and Circular Dichroism spectroscopy (CD). The effect of the surface characteristics of liposomes, which were composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and modified with cholesterol (Ch) or 1,2-dioleoyl-3-trimethylammonium propane (DOTAP), on the liposome–RNA interaction was investigated. The fluorescence of 6-(p-toluidino)naphthalene-2-sulfonate (TNS) embedded in the liposome surface (ε = 30–40) was decreased in the presence of tRNA, suggesting that single-stranded tRNA could bind onto the liposome. The dehydration of –PO₂⁻ –, guanine (G) and cytosine (C) of tRNA molecules in the presence of liposomes suggested both an electrostatic interaction (phosphate backbone of tRNA and trimethylammonium group of POPC, DOTAP) and a hydrophobic interaction (guanine or cytosine of tRNA and aliphatic tail of lipid). The tRNA conformation on the liposome was determined by CD spectroscopy. POPC/Ch (70/30) maintained tRNA conformation without any denaturation, while POPC/DOTAP(70/30) drastically denatured it. The mRNA translation was evaluated in an Escherichia coli cell-free translation system. POPC/Ch(70/30) enhanced expression of green fluorescent protein (GFP) (116%) while POPC/DOTAP(70/30) inhibited (37%), suggesting that the conformation of RNAs was closely related to the translation efficiency. Therefore, single-stranded RNAs could bind to liposomal membranes through electrostatic and hydrophobic attraction, after which conformational changes were induced depending on the liposome characteristics.

Oxidative stress can affect the gene silencing effect of DOTAP liposome in an in vitro translation system

Oxidative stress can affect in vitro GFP expression through its control of the gene silencing effect of the liposome prepared by 1,2-dioleoyl-3-trimethyl-ammonium propane (DOTAP). The gene silencing effect of cationic DOTAP liposome in in vitro GFP expression, especially focusing on its translation process, and the effects of oxidative stress on its silencing effect were investigated. GFP expression, initiated by mRNA, was found to be thoroughly inhibited in the presence of DOTAP liposome at concentration of more than 2.5 mM, though its inhibitory effect was reduced in the presence of hydrogen peroxide. The analyses of (i) the interaction of mRNA with DOTAP, (ii) the chemical structure of DOTAP, and (iii) the membrane fluidity of DOTAP liposome imply the possible role of gene expression by the liposome membrane and stress conditions.

Optimization and quantification of protein synthesis inside liposomes

Synthetic biology aims at reprogramming existing, or creating new, biological systems, with the ultimate aim to obtain artificial cells whose functions can be tailored. For the latter, encapsulation of complex biochemical reactions into cell-sized compartments, such as liposomes, is required. Recently, several groups have demonstrated that proteins of interest can be produced de novo within liposomes by entrapping cell-free protein-synthesis systems and DNA templates inside liposomes. Although detectable, intraliposomal protein synthesis was generally poor. Here, we have optimized intraliposomal cell-free protein synthesis by changing several variables, including lipid composition as well as liposome, pyrophosphatase, and T7 RNA polymerase concentration. Further, by using an activity-based assay, we have quantified the amount of full-length protein that was produced from DNA templates inside liposomes before and after optimization of aforementioned variables. Based on the model protein beta-galactosidase, it is demonstrated that liposomal protein synthesis can yield microgram quantities of protein (30-40 microg/mL liposomes).

Liposomes destabilize tRNA during heat stress

Biomembranes play an important role in cellular response to heat stress. In this study, we focus on the interaction between liposomes and tRNA. Upon heat treatment we determined circular dichroism spectra of tRNA in presence of liposomes prepared from POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and cholesterol (Ch). To compare thermal stability, midpoint temperature (T(m)) of tRNA was calculated from normalized theta(208). Addition of POPC/Ch liposomes decreased the T(m) value of tRNA from 48 degrees C to 38 degrees C. We conclude that POPC/Ch liposomes interact with tRNA and destabilize its conformation under heat stress.

Cellular compartment model for exploring the effect of the lipidic membrane on the kinetics of encapsulated biochemical reactions

One of the important characteristics of the cellular system is that interactions between the plasma membrane and water-soluble molecules in the cytoplasm are enhanced by the confinement of the molecules to the small volume of the intracellular space. Studying this effect in a model cell system, we measured the time evolution of an enzymatic hydrolysis reaction and a cell-free protein synthesis reaction taking place in giant liposomes having various size and phospholipid compositions by a flow cytometry. This single vesicle-based assay of a large number of liposomes enabled us to examine the volume dependence of enclosed reactions in detail, revealing that the presence of specific lipid affected the specific kinetic parameters of encapsulated reactions.

Chitosanase displayed on liposome can increase its activity and stability

The strategy to prepare a novel biocatalyst by the immobilization of chitosanase onto liposome (ICL) was carried out based on the direct interaction of liposomes with cell membrane of Streptomyces griseus cell. The ICL was characterized in relation to the molecular weight of protein, the chitosanase activity, the effect of the surface hydration of various liposomes on hydrolysis activity of immobilized chitosanase and the stability of ICL under various extreme conditions. The SDS-PAGE analysis of the purified ICL sample shows the existence of a protein with approximately 39kDa that corresponded to the sum of weight of the mature chitosanase and its signal peptide (38.8kDa). The above protein of ICL also expresses the chitosanase activity that is significantly higher than that of the conventional chitosanase. Furthermore, the surface hydration of liposomes used to prepare ICL that affected the activity of immobilized chitosanase verified the importance of liposome surfaces. Indeed, the stability of ICL assayed by measuring the chitosanase activity is significantly higher than that of conventional chitosanase under various temperatures and pH conditions. These characteristics of ICL show the possible preparation of the biocatalysts that can be prepared by immobilizing enzymes onto liposome vesicles properly.