Biology subjects

Engelhart, A. E.

Publications and source records attributed to Engelhart, A. E..

At least 19 recordsLinked to original sources

bioRxiv2026

Programming Metabolic Dependency in Synthetic Cells Under Resource Scarcity

Engineering synthetic cells where metabolism directly controls gene expression is one of the greatest challenges in synthetic biology. This coupling between metabolic activity and protein synthesis is also thought to have been a vital step in the evolution of the earliest cellular life. This fundamental process is essential for developing minimal, self-sustaining cells, both engineered for biotechnology applications and as models explaining the origins of life. Here, we present a programmable cell-free platform that links metabolic activity to translation under defined resource limitations. Using an engineered amino-acid-dependent cell-free translation system, we introduced a tunable metabolic bottleneck (depleting tyrosine). This enabled imposing a controlled metabolic constraint on protein synthesis. To alleviate this constraint, we then incorporated phenylalanine hydroxylase (PAH) as a minimal module for tyrosine synthesis. The PAH-driven tyrosine synthesis established a system in which protein expression is directly controlled by amino acid biosynthesis. This relationship was recapitulated in liposome compartments, resulting in three distinct synthetic cell populations. The metabolically active population had significantly higher fitness in protein production. Overall, this work establishes an experimentally tractable platform to investigate how primitive cells may have evolved internal metabolic capabilities, and it represents a foundational step toward constructing more autonomous and self-regulating synthetic cells.

biochemistry↗

bioRxiv2026

A Chemically Defined Synthetic Cell Capable Of Growth And Replication

Cells are the fundamental unit of life. Yet there is no natural cell for which all its life-essential functions are understood. Here we demonstrate a complete cell cycle for a synthetic cell undergoing selection, with genome replication, growth, resource acquisition via feeding, and genetically encoded division. The cell is encoded via a 90kb genome that includes functions needed for resource uptake, transcription, translation, growth, genome replication, and division. The resulting synthetic cell is sufficiently encouraging to support routinization of synthetic cell engineering workflows, and will ultimately underlie diverse applications across all of biotechnology.

synthetic biology↗

bioRxiv2025

One-pot cloning and protein expression platform for genetic engineering

In this work, we present a streamlined one-pot cloning and protein expression platform that integrates mutagenesis, plasmid assembly, and functional protein testing in a single reaction. By combining Golden Gate cloning with cell-free transcription-translation, we demonstrate efficient generation and screening of genetic variants without the need for intermediate purification or bacterial amplification. Using fluorescent proteins, luciferase enzymes, antibiotic-converting enzymes, and the violacein biosynthetic pathway, we validate the versatility of this approach for single-and multi-site mutagenesis, combinatorial variant libraries, metabolic pathway programming, and whole-plasmid assembly. By demonstrating compatibility with multiplexed reactions and multi-cistronic constructs, we establish this approach as a generalizable and automatable method for high-throughput cloning and protein engineering in synthetic biology.

bioengineering↗

bioRxiv2025

An Expanded Repertoire of tRNA Sources for Cell-Free Protein Synthesis

Cell-free expression systems (CFE) are flexible protein translation platforms that simplify the central dogma into an accessible reaction space. Within these systems, bulk transfer RNAs (tRNAs) are critical substrates which deliver amino acids to the elongating ribosome. For years, CFE systems were completed with commercially available tRNA isolated from E. coli MRE600. All commercial sources of tRNA have since been discontinued, jeopardizing future work in all applications of cell-free translation. Here, we address this need by repurposing previously described tRNA isolation methods to produce tRNAs suitable for CFE applications. We isolated the tRNA pools of E. coli strains A19, BL21(DE3), and Rosetta2 BL21(DE3), finding A19 tRNAs but not BL21(DE3) or Rosetta2 BL21(DE3) capable of robust in vitro translation. We determined the abundances of individual tRNAs using tRNA-seq, finding BL21(DE3) and Rosetta2 BL21(DE3) contained outsized abundances of several tRNAs, compromising translation activity. Using codon optimization strategies which align codon usage to tRNA abundance, we were able to mitigate the impact of misaligned tRNA abundances. We extended these studies to V. natriegens, a promising platform for synthetic biology and CFE. We find that neither exogenous V. natriegens tRNAs nor codon optimization are viable options to improve translation yields. Our work here highlights the importance of tRNA abundance within the context of CFE, and simultaneously addresses a critical challenge within cell-free translation.

biochemistry↗

bioRxiv2025

Purification of post-transcriptionally modified tRNAs for enhanced cell-free translation systems

Transfer RNAs (tRNAs) are utilized by the ribosome to decode the nucleic acid alphabet. tRNA structure, stability, aminoacylation efficiency, and decoding efficacy are governed by their extensive post-transcriptional modifications. In most studies, individual tRNAs are generated using in vitro transcription, which produces tRNAs devoid of these critical site-specific modifications, negatively affecting translation yields and fidelity. To address this, we have developed a purification method which couples tRNA overexpression to DNA hybridization-based purification. Using this approach, we produced native tRNAs from E. coli in high yield and purity while retaining their complement of native post-transcriptional modifications and translational activity. We extend this technique to the purification of [Formula] and [Formula], tRNAs of critical importance for genetic code expansion. We confirmed that both [Formula] and [Formula] contain native E. coli post-transcriptional modifications and provide the first complete modification profiles of each. Moreover, we found that in vivo-generated [Formula] significantly outperforms its in vitro-generated counterpart in amber codon suppression in cell-free translation reactions. Finally, we purified an engineered variant of E. coli [Formula], extending our studies to synthetic tRNAs. We present a flexible method which generates modified tRNAs in high yield and purity, addressing a critical and persistent challenge in RNA biochemistry. This toolkit enables future structural and cell-free studies through scalable access to native and engineered tRNAs, advancing the broader field of translation and synthetic biology.

biochemistry↗

bioRxiv2024

Nonenzymatic, prebiotic aminoacylation couples chirality of RNA and protein

Life as we know it depends on the homochirality of nucleic acids and proteins. However, there is no widely accepted explanation for why life uses only D-sugars for nucleic acids and L-amino acids for proteins. Here we demonstrate a prebiotically plausible method of nonenzymatic aminoacylation in a water ice-eutectic phase. These reactions produce high yields of aminoacyl-tRNAs, which are active in translation. Surprisingly, we discovered these nonenzymatic aminoacylation conditions were stereoselective, favoring coupling of amino acids and RNA of "opposite" L- and D- configurations. D-RNA shows greater aminoacylation yields for L-amino acids. The opposite was true for L-RNA, which had greater yields with D-amino acids. Nucleic acid backbone chirality influencing stereoselectivity of aminoacylation presents the missing link in the origin of modern biochemistry. This phenomenon provides insight into the chirality of the RNA world, and helps to explain the "opposite" stereochemistry of modern biomolecules.

biochemistry↗

bioRxiv2024

Alternate conformational trajectories in protein synthesis

Translocation in protein synthesis entails the efficient and accurate movement of the mRNA-[tRNA]2 substrate through the ribosome after peptide bond formation. An essential conformational change during this process is the swiveling of the small subunit head domain about two rRNA hinge elements. Using directed evolution and molecular dynamics simulations, we derive alternate hinge elements capable of translocation in vitro and in vivo and describe their effects on the conformational trajectory of the EF-G-bound, translocating ribosome. In these alternate conformational pathways, we observe a diversity of swivel kinetics, hinge motions, three-dimensional head domain trajectories and tRNA dynamics. By finding alternate conformational pathways of translocation, we identify motions and intermediates that are essential or malleable in this process. These findings highlight the plasticity of protein synthesis and provide a more thorough understanding of the available sequence and conformational landscape of a central biological process. Author SummaryTranslocation, the motion of the ribosome across its mRNA substrate, is an essential stage of protein synthesis. A key conformational change in this process is the rotation of the ribosome head domain about two rRNA hinges in the direction of translocation, repositioning the mRNA and tRNAs in their final states. Employing directed evolution, we obtain variant hinges capable of performing translocation in vitro and in vivo. Through molecular dynamics simulations, the different variant ribosome translocation conformational trajectories are described. This description reveals different possible conformational pathways to translocation, with varying dynamics, motions and intermediates. The understanding of this conformational malleability can increase our knowledge of protein synthesis function, disruption, evolution, and engineering.

synthetic biology↗

bioRxiv2024

Quencher-free fluorescence monitoring of G-Quadruplex folding

Guanine-rich sequences exhibit a high degree of polymorphism and can form single-stranded, Watson-Crick duplex, and four-stranded G-quadruplex structures. These sequences have found a wide range of uses in synthetic biology applications, arising in part from their structural plasticity. High-throughput, low-cost tools for monitoring the folding and unfolding transitions of G-rich sequences would provide an enabling technology for accelerating prototyping of synthetic biological systems and for accelerating design-build-test cycles. Here, we show that unfolding transitions of a range of G-quadruplex-forming DNA sequences can be monitored in a FRET-like format using DNA sequences that possess only a single dye label, with no quencher. These quencher-free assays can be performed at low cost, with both cost and lead times ca. 1 order of magnitude lower than FRET-labeled strands. Thus, quencher-free secondary structure monitoring promises to be a valuable tool for testing and development of synthetic biology systems employing G-quadruplexes.

biophysics↗

bioRxiv2023

High yield, low magnesium flexizyme reactions in a water-ice eutectic phase

Flexizymes enable the stoichiometric acylation of tRNAs with a variety of compounds, enabling the in vitro translation of peptides with both non-natural backbones and side chains. However, flexizyme reactions have several drawbacks, including single-turnover kinetics, high Mg(II) carryover inhibiting in vitro translation, and rapid product hydrolysis. Here we present flexizyme reactions utilizing an ice-eutectic phase, with high yields, 30X lower Mg(II), and long-term product stability. The eutectic flexizyme reactions increase the ease of use and flexibility of flexizyme aminoacylation, and increase the in vitro protein production.

synthetic biology↗

bioRxiv2023

Emergent functional behaviors of ribozymes in oxychlorine brines indicate Mars could host a unique niche for molecular evolution

Mars is a particularly attractive candidate among known astronomical objects to potentially host life. Results from space exploration missions have provided insights into Martian geochemistry indicating oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to its toxicity. However, it can also provide potential benefits, such as producing brines by deliquescence, like those thought to exist on present-day Mars. Here we show perchlorate brines support folding and catalysis of functional RNAs, while inactivating representative protein enzymes. Additionally, we show perchlorate and other oxychlorine species enable new ribozyme functions, including homeostasis-like regulatory behavior, copying of structured RNAs, and the first ribozyme-catalyzed chlorination of organic molecules. We suggest nucleic acids are uniquely well-suited to hypersaline Martian environments. Furthermore, Martian near-or subsurface oxychlorine brines, and brines found in potential lifeforms, could provide a unique niche for biomolecular evolution.

biochemistry↗

bioRxiv2023

Sequential gentle hydration increases encapsulation in model protocells

Small, spherical vesicles are a widely used chassis for the formation of model protocells and investigating the beginning of compartmentalized evolution. Various methods exist for their preparation, with one of the most common approaches being gentle hydration, where thin layers of lipids are hydrated with aqueous solutions and gently agitated to form vesicles. An important benefit to gentle hydration is that the method produces vesicles without introducing any organic contaminants, such as mineral oil, into the lipid bilayer. However, compared to other methods of liposome formation, gentle hydration is much less efficient at encapsulating aqueous cargo. Improving the encapsulation efficiency of gentle hydration would be of broad use for medicine, biotechnology, and protocell research. Here, we describe a method of sequentially hydrating lipid thin films to increase encapsulation efficiency. We demonstrate that sequential gentle hydration significantly improves encapsulation of water-soluble cargo compared to the traditional method, and that this improved efficiency is dependent on buffer composition. Similarly, we also demonstrate how this method can be used to increase concentrations of oleic acid, a fatty acid commonly used in origins of life research, to improve the formation of vesicles in aqueous buffer.

biochemistry↗

bioRxiv2022

New Aequorea fluorescent proteins for cell-free bioengineering

Recently, a new subset of fluorescent proteins has been identified from the Aequorea species of jellyfish. These fluorescent proteins were characterized in vivo; however, there has not been validation of these proteins within cell-free systems. Cell-free systems and technology development is a rapidly expanding field, encompassing foundational research, synthetic cells, bioengineering, biomanufacturing and drug development. Cell-free systems rely heavily on fluorescent proteins as reporters. Here we characterize and validate this new set of Aequorea proteins for use in a variety of cell-free and synthetic cell expression platforms. O_FIG O_LINKSMALLFIG WIDTH=144 HEIGHT=200 SRC="FIGDIR/small/519681v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@3a3100org.highwire.dtl.DTLVardef@672233org.highwire.dtl.DTLVardef@f65f32org.highwire.dtl.DTLVardef@e40aaf_HPS_FORMAT_FIGEXP M_FIG C_FIG

synthetic biology↗

bioRxiv2022

A gene expression control technology for cell-free systems and synthetic cells via targeted gene silencing and transfection

Cell-free transcription-translation (TXTL) is an in vitro protein expression platform. In synthetic biology, TXTL is utilized for a variety of technologies, such as genetic circuit construction, metabolic pathway optimization, and building prototypes of synthetic cells. For all these purposes, the ability to precisely control gene expression is essential. Various strategies to control gene expression in TXTL have been developed; however, further advancements on gene-specific and straightforward regulation methods are still demanded. Here, we designed a novel method to control gene expression in TXTL, called a "silencing oligo." The silencing oligo is a short oligonucleotide that binds to the target mRNA. We demonstrated that addition of the silencing oligo inhibits eGFP expression in TXTL in a sequence-dependent manner. We investigated one of the silencing oligos inhibitory mechanisms and confirmed that silencing is associated with RNase H activity in bacterial TXTL reactions. We also engineered a transfection system that can be used in synthetic cells. We screened two dozen different commercially available transfection reagents to identify the one that works most robustly in our system. Finally, we combined the silencing oligo with the transfection technology, demonstrating that we can control the gene expression by transfecting silencing oligo-containing liposomes into the synthetic cells.

synthetic biology↗

bioRxiv2022

Parasites, infections and inoculation in synthetic minimal cells

Synthetic minimal cells provide a controllable and engineerable model for an increasing amount of biological processes. While much simpler than any live natural cell, synthetic cells offer a chassis for investigating the foundations of key biological processes. Here we show a synthetic cell system describing host cells interacting with parasites and infections of varying severity. We demonstrate how the host can be engineered to resist infection, we investigate the metabolic cost of carrying resistance, and we show a simple inoculation system that immunizes the host against pathogens. Our work expands the synthetic cell engineering toolbox by demonstrating host pathogen interactions and mechanisms for acquiring immunity. This brings synthetic cell systems one step closer to providing a comprehensive model of complex, natural life.

synthetic biology↗

bioRxiv2022

Expanding luciferase reporter systems for cell-free protein expression

Luciferases are often used as a sensitive, versatile reporter in cell-free transcription-translation (TXTL) systems, for research and practical applications such as engineering genetic parts, validating genetic circuits, and biosensor outputs. Currently, only two luciferases (Firefly and Renilla) are commonly used without substrate cross-talk. Here we demonstrate expansion of the cell-free luciferase reporter system, with two orthogonal luciferase reporters: N. nambi luciferase (Luz) and LuxAB. These luciferases do not have cross-reactivity with the Firefly and Renilla substrates. We also demonstrate a substrate regeneration pathway for one of the new luciferases, enabling long-term time courses of protein expression monitoring in the cell-free system. Furthermore, we reduced the number of genes required in TXTL expression, by engineering a cell extract containing part of the luciferase enzymes. Our findings lead to an expanded platform with multiple orthogonal luminescence translation readouts for in vitro protein expression.

synthetic biology↗

bioRxiv2022

Controlled exchange of protein and nucleic acid signals from and between synthetic minimal cells

Synthetic minimal cells are a class of small liposome bioreactors that have some, but not all functions of live cells. Here, we report a critical step towards the development of a bottom-up minimal cell: cellular export of functional protein and RNA products. We used cell penetrating peptide tags to translocate payloads across a synthetic cell vesicle membrane. We demonstrated efficient transport of active enzymes, and transport of nucleic acid payloads by RNA binding proteins. We investigated influence of a concentration gradient alongside other factors on the efficiency of the translocation, and we show a method to increase product accumulation in one location. We demonstrate the use of this technology to engineer molecular communication between different populations of synthetic cells, to exchange protein and nucleic acid signals. The synthetic minimal cell production and export of proteins or nucleic acids allows experimental designs that approach the complexity and relevancy of natural biological systems.

synthetic biology↗

bioRxiv2021

Akaby - cell-free protein expression system for linear templates

Cell-free protein expression is increasingly becoming popular for biotechnology, biomedical and research applications. Among cell-free systems, the most popular one is based on Escherichia coli (E. coli). Endogenous nucleases in E. coli cell-free transcription-translation (TXTL) degrade the free ends of DNA, resulting in inefficient protein expression from linear DNA templates. RecBCD is a nuclease complex that plays a major role in nuclease activity in E. coli, with the RecB subunit possessing the actual nuclease activity. We created a RecB knockout of an E. coli strain optimized for cell-free expression. We named this new strain Akaby. We demonstrated that Akaby TXTL successfully reduced linear DNA degradations, rescuing the protein expression efficiency from the linear DNA templates. The practicality of Akaby for TXTL is an efficient, simple alternative for linear template expression in cell-free reactions. We also use this work as a model protocol for modifying the TXTL source E. coli strain, enabling the creation of TXTL systems with other custom modifications.

synthetic biology↗

bioRxiv2021

T7Max transcription system

Efficient cell-free protein expression from linear DNA templates has remained a challenge primarily due to template degradation. Here we present a modified T7 RNA polymerase promoter that acts to significantly increase the yields of both transcription and translation within in vitro systems. The modified promoter, termed T7Max, recruits standard T7 RNA polymerase, so no protein engineering is needed to take advantage of this method. This technique could be used with any T7 RNA polymerase-based in vitro protein expression system. Unlike other methods of limiting linear template degradation, the T7Max promoter increases transcript concentration in a T7 transcription reaction, providing more mRNA for translation.

synthetic biology↗