Biology subjects

Erb, T. J.

Publications and source records attributed to Erb, T. J..

At least 19 recordsLinked to original sources

bioRxiv2026

Directed evolution of the Fe-nitrogenase for CO2 reduction to hydrocarbons

The iron (Fe) nitrogenase drives bacterial methane (CH4) formation by converting carbon dioxide (CO2) to CH4 in a single enzymatic step. Enhancing the initial CH4 formation activity of Fe-nitrogenase and expanding the product spectrum to hydrocarbon chains could lead to a route for sustainable feedstock chemicals. Here, we performed the first directed evolution campaign on the Fe-nitrogenase aimed at optimizing the hydrocarbon production. We achieved an [~]8-fold increase in CH4 formation by Fe-nitrogenase expressing Rhodobacter capsulatus cultures in three rounds of site-saturation mutagenesis. The best performing mutant (F362ManfD, Y85FanfD, T360SanfD) extends the in vivo product spectrum of the nitrogenase to ethane (C2H6) and exhibits 6-fold higher rates for CO production in vitro, whereas the formation of the undesirable byproduct formate was abolished. Electron microscopy-based structural analysis identified a methionine and water potentially stabilizing the transition state and fine-tuning the CO2 reduction mechanism and activity.

biochemistry↗

bioRxiv2026

Chemically tunable permeability of engineered alpha-Hemolysin in synthetic cells

Controlling molecular transport across membranes is a defining feature of living cells, yet replicating this functionality in synthetic systems remains a major challenge. Self-inserting protein nanopores, such as -hemolysin (HL), offer a promising route towards programmable membrane permeability due to their robust assembly, compatibility with diverse membrane systems, and intrinsic permeability for diverse biomolecules. Here, we explored the use of chemically functionalized HL nanopores as tunable transport modules. To quantify translocation of peptide substrates across HL-containing membranes, we developed a high-throughput luminescence-based breakage-controlled assay using large unilamellar vesicles. With this assay we introduce a one-pot nanopore modification and strategy, compatible with scalable workflows. Electrophysiology and molecular simulations demonstrate that the introduction of cysteine residues at defined pore locations, combined with targeted chemical modification, enables controlled tuning of HL-nanopore selectivity based on peptide structure and charge. Together, these findings position engineered protein nanopores as versatile and responsive components for controlling membrane transport in synthetic biology.

synthetic biology↗

bioRxiv2026

Form IF Rubiscos include highly active, specific, and small subunit-independent enzymes.

Plant-type (Form I) Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) suffers from inherent catalytic trade-offs and a strong dependency on other proteins--including an essential small subunit (SSU) and auxiliary chaperones--for assembly, constraining the enzymes evolutionary and engineering potential. Here, we investigated representatives from the newly discovered clade Form IF. These enzymes do not require specific chaperones to form functional complexes, exhibit high CO2-specificities (SC/O [~]50) while maintaining high turnover rates (up to kcat [~]11 s-1). Remarkably, two Form IF representatives (IF-1/IF-2) lost the dependency on the SSU and assemble into homo-octameric complexes without their cognate SSUs. While the SSU is not necessary for catalysis, its addition improves both activity and specificity in IF-1/IF-2. Our results show that complexity is actually not required to achieve highly active, specific and functional Rubisco variants--and that this complexity can even be reverted--which challenges our current thinking on the evolution and catalytic mechanism of Rubisco.

biochemistry↗

bioRxiv2026

Combining evolution and machine learning-guided pathway optimization to engineer a novel methylsuccinate module for synthetic C1 metabolism in vivo

De novo metabolic pathways open possibilities for sustainable biotransformations in microbes. However, the in vivo-implementation of such new-to-nature pathways is highly challenging and heavily relies on adaptive laboratory evolution (ALE) of the hosts native metabolic network. Here, we assess how much this need for host-centric ALE can be overcome and/or complemented through the informed design of the newly introduced pathway. Exemplifying for a synthetic CO2-fixation module via methyl-succinate, we established methylsuccinate-dependent growth of Escherichia coli over six months by ALE of E. colis native metabolism. In parallel, we developed a machine-learning guided workflow (MEVIS) for the automated engineering of the synthetic pathway, resulting in methylsuccinate-dependent growth within three weeks. Critically, performing MEVIS in the background of the ALE-evolved strain is necessary to further approach wild-type like growth, demonstrating how ALE in combination with machine-learning-guided lab automation holds great potential to accelerate and improve design-build-test-learn cycles in contemporary metabolic engineering.

bioengineering↗

bioRxiv2025

Functional Mapping and Engineering of the Sec Translocon Unlocked by a Cell-Free System

Almost all proteins are inserted or translocated across membranes by the universally conserved Sec translocon. Despite its central role, experimental access to Sec function has remained limited. Here, we present a cell-free protein synthesis platform that inserts SecYEG into synthetic vesicles, enabling direct testing of Sec in real-time and high-throughput, circumventing longstanding viability constraints. Screening 300 Sec variants in a single experiment, we consolidate three decades of Sec research, while vastly expanding mutant diversity for structure-function insights. Mapping over 30 functionally critical regions that modulate Sec activity across three orders of magnitude, we uncover dozens of super-active variants. We further leverage our system to increase membrane protein quality and nanobody export, highlighting the potential of our system for advancing applications in synthetic biology and biotechnology.

molecular biology↗

bioRxiv2025

Modular in vivo engineering of the reductive methylaspartate cycles for synthetic CO2 fixation

Biological carbon fixation is currently limited to seven naturally occurring pathways. Synthetic carbon fixation pathways have the potential to surpass aerobic natural pathways in efficiency, but none have been realized in living cells. Here, we present the reductive methylaspartate cycles (rMASP), a novel family of 4 energy-efficient aerobic CO2 fixation pathway variants. These cycles have the potential to outperform the yields and/or rates of the Calvin cycle and previously proposed synthetic CO2 fixation cycles. To realize these designs, we adopted a modular engineering approach in Escherichia coli. Several pathway modules up to a cascade of 11 enzymes were realized via engineering and evolution. We demonstrate crotonyl-CoA carboxylase dependent growth for both elevated and ambient CO2 conditions, and show in vitro activity of the other CO2-fixing 2-oxoglutarate carboxylase, which requires further activity optimization for mesophilic temperatures. This work demonstrates important steps toward realizing efficient synthetic carbon fixation pathways in living organisms.

synthetic biology↗

bioRxiv2025

Evolution-assisted engineering of formate assimilation via the formyl phosphate route in Escherichia coli

The transition towards a sustainable bioeconomy requires the use of alternative feedstocks, with CO2-derived formate emerging as a promising candidate for industrial biotechnology. Despite its beneficial characteristics as a feedstock, microbial assimilation of formate is limited by the inefficiency of naturally evolved formate-fixing pathways. To overcome this limitation, synthetic formate reduction cascades could enable formate assimilation via formaldehyde, a key intermediate of several existing one carbon assimilation pathways. Recently, the formyl phosphate route, combining ATP-dependent activation of formate to formyl phosphate, followed by its reduction to formaldehyde, was developed through enzyme engineering and characterized in vitro. In this work, we successfully established the formyl phosphate route in vivo by developing a selection strategy that couples formate reduction to growth in a threonine/methionine auxotrophic Escherichia coli. Through adaptive laboratory evolution, we achieved formate-dependent growth via this novel pathway. Evolved strains were capable of growing robustly with formate concentrations between 20 mM and 100 mM with glucose in the co-feed. Genomic and proteomic analyses together with activity assays uncovered that formate activation was limiting in vivo. This discovery guided the rational engineering of a strain capable of efficient formate assimilation through the formyl phosphate route. By demonstrating that novel enzyme activities can link formate reduction to cell growth, our study shows how synthetic metabolic routes can be functionally established inside the cell, paving the way for the engineering of more complex synthetic pathways.

bioengineering↗

bioRxiv2025

Origin of chaperone dependence and assembly complexity in Rubisco biogenesis

Molecular chaperones assist with the folding and assembly of protein clients. Consequently, they are essential to diverse cellular functions. In most aerobic photosynthetic organisms such as {beta}-cyanobacteria and all plants, the key CO2-fixing enzyme Rubisco strictly relies on dedicated chaperones for its assembly. Why these chaperones were recruited is unclear, as they are absent and not required in other prokaryotic autotrophs. By retracing the evolution of Rubisco-chaperone interactions, we find that Rubiscos dependence on chaperones evolved neutrally and not by adaptive optimization, and that this may be reversed without compromising catalytic function. Our work shows how chaperones are broad modifiers of their clients sequence spaces that can become totally essential through non-adaptive processes.

evolutionary biology↗

bioRxiv2025

Genetically encoded control of in vitro transcription-translation coupled DNA replication

The bottom-up reconstruction of cellular functions has gained increasing attention for studying biological complexity, and for developing advanced biotechnological tools, including synthetic cells. A fundamental challenge is the ability to control and replicate DNA-encoded information within basic in vitro transcription-translation (IVTT) systems. Here, we constructed a transcription-translation coupled DNA replication (TTcDR) system that is based on a modified PURE (Protein synthesis Using Recombinant Elements) IVTT system and {Phi}29 DNA polymerase, which is controlled by external signals. To this end, we first established and characterized a PUREfrex 1.0-based TTcDR system. We then constructed and optimized TetR-based control of TTcDR activity, either by DNA-encoding TetR or by supplying purified TetR. Our final DNA-encoded TetR circuit allows [~]1000-fold DNA replication, [~]100-fold repression, and [~]4-fold induction with anhydrotetracycline. Our results demonstrate the potential and challenges of controlling in vitro DNA replication, for example for the evolution of in vitro systems. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=178 SRC="FIGDIR/small/663768v1_ufig1.gif" ALT="Figure 1"> View larger version (22K): org.highwire.dtl.DTLVardef@cff8fcorg.highwire.dtl.DTLVardef@1e3751dorg.highwire.dtl.DTLVardef@1e037corg.highwire.dtl.DTLVardef@76f330_HPS_FORMAT_FIGEXP M_FIG C_FIG

synthetic biology↗

bioRxiv2025

Systematic engineering of synthetic serine cycles in Pseudomonas putida uncovers emergent topologies for methanol assimilation

The urgent need for a circular carbon economy has driven research into sustainable substrates, including one-carbon (C1) compounds. The non-pathogenic soil bacterium Pseudomonas putida is a promising host for exploring synthetic methylotrophy due to its versatile metabolism. In this work, we implemented synthetic serine cycle variants in P. putida for methanol assimilation combining modular engineering and growth-coupled selection, whereby methanol assimilation supported biosynthesis of the essential amino acid serine. The serine cycle forms acetyl-coenzyme A from C1 molecules without carbon loss but has bottlenecks that hinder engineering efforts. We adopted three synthetic variants (serine-threonine cycle, homoserine cycle, and modified serine cycle) that yield serine in a methanol-dependent fashion to overcome these challenges. By dividing these metabolic designs into functional modules, we systematically compared their performance for implementation in vivo. Additionally, we harnessed native pyrroloquinoline quinone-dependent dehydrogenases for engineering methylotrophy. Recursive rewiring of synthetic and native activities revealed novel metabolic topologies for methanol utilization, termed enhanced serine-threonine cycle, providing a blueprint for engineering C1 assimilation in non-model heterotrophic bacteria. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=168 SRC="FIGDIR/small/638773v1_ufig1.gif" ALT="Figure 1"> View larger version (79K): org.highwire.dtl.DTLVardef@1bfccd0org.highwire.dtl.DTLVardef@11f77deorg.highwire.dtl.DTLVardef@f6a904org.highwire.dtl.DTLVardef@1d24a34_HPS_FORMAT_FIGEXP M_FIG C_FIG

synthetic biology↗

bioRxiv2024

Rewiring Escherichia coli to Transform Formate into Methyl Groups

BackgroundBiotechnological applications are steadily growing and have become an important tool to reinvent the synthesis of chemicals and pharmaceuticals for lower dependence on fossil resources. In order to sustain this progression, new feedstocks for biotechnological hosts have to be explored. One-carbon (C1-)compounds, including formate, derived from CO2 or organic waste are accessible in large quantities with renewable energy, making them promising candidates. Previous studies showed that introduction of the formate assimilation machinery from Methylorubrum extorquens into Escherichia coli allows assimilation of formate into the established biotechnological host. Applying this established route for formate assimilation, we here investigated utilisation of formate for the production of value-added building blocks in E. coli using S-adenosylmethionine (SAM)-dependent methyltransferases. ResultsWe first analysed methylation activity in E. coli BL21 with a two-vector system to produce three different methyltransferases together with the formate assimilation machinery. Feeding isotopically labelled formate, products with 51 - 81% 13C-labelling could be obtained by maintaining in vivo methylation activity. Focussing on improvement of in vivo methylation, we analysed two further E. coli strains with an engineered C1-metabolism and, following condition optimisation, achieved a doubled methylation activity with a share of more than 70% formate-derived methyl groups. ConclusionsThis study demonstrates the efficient transformation of formate into methyl groups in E. coli. Our findings support that feeding formate can improve the availability of usable C1-compounds and, as a result, increase in vivo methylation activity in engineered E. coli.

biochemistry↗

bioRxiv2024

System-level characterization of engineered and evolved formatotrophic E. coli strains

One-carbon compounds, such as formate, are promising and sustainable feedstocks for microbial bioproduction of fuels and chemicals. Growth of Escherichia coli on formate was recently achieved by introducing the reductive glycine pathway (rGlyP) into its genome, which is theoretically the most energy-efficient aerobic formate assimilation pathway. While adaptive laboratory evolution was used to enhance the growth rate and biomass yield significantly, still the best performing formatotrophic E. coli strain did not approach the theoretical optimal biomass yield of the rGlyP. In this study, we investigated these previously engineered formatotrophic E. coli strains to find out why the biomass yield was sub-optimal and how it may be improved. Through a combination of metabolic modelling, genomic and proteomic analysis, we identified several potential metabolic bottlenecks and future targets for optimization. This study also reveals further insights in the evolutionary mutations and related changes in proteome allocation that supported the already substantially improved growth of formatotrophic E. coli strain. This systems-level analysis provides key insights to realize high-yield, fast growing formatotrophic strains for future bioproduction.

synthetic biology↗

bioRxiv2024

Expanding the biotechnological scope of metabolic sensors through computation-aided designs

Metabolic sensors are microbial strains modified so that biomass formation correlates with the availability of specific metabolites. These sensors are essential for bioengineering (e.g. in growth-coupled designs) but creating them is often a time-consuming and low-throughput process that can potentially be streamlined by in silico analysis. Here, we present the systematic workflow of designing, implementing, and testing versatile Escherichia coli metabolic sensor strains. Glyoxylate, a key metabolite in (synthetic) CO2 fixation and carbon-conserving pathways, served as the test molecule. Through iterative screening of a compact metabolic model, we identified non-trivial growth-coupled designs that resulted in six metabolic sensors with a wide sensitivity range for glyoxylate, spanning three orders of magnitude in detected concentrations. We further adapted these E. coli strains for sensing glycolate and demonstrated their utility in both pathway engineering (testing a key metabolic module via glyoxylate) and applications in environmental monitoring (quantifying glycolate produced by photosynthetic microalgae). The versatility and ease of implementation of this workflow make it suitable for designing and building multiple metabolic sensors for diverse biotechnological applications. TeaserA streamlined workflow enables the rapid design of versatile E. coli metabolic sensors for detecting key metabolites in bioengineering and monitoring.

synthetic biology↗

bioRxiv2024

Bottom-up reconstruction of minimal pyrenoids provides insights into the evolution and mechanisms of carbon concentration by EPYC1 proteins

Membraneless organelles play essential roles in cellular processes. In various photosynthetic organisms, they confer carbon concentrating mechanisms (CCMs). One example is the pyrenoid in Chlamydomonas reinhardtii, a liquid-phase separated organelle that localizes and improves carbon fixation via the intrinsically-disordered protein (IDP) EPYC1. Modern-day pyrenoids are complex structures, which makes it impossible to study the function of EPYC1, especially whether EPYC1 alone confers carbon concentration, and how EPYC1 could have initiated the evolution of pyrenoids. Here, we developed a bottom-up approach to study the function of EPYC1 and its sequence-function space across evolution. We demonstrate that modern-day EPYC1-sequences, but not other IDPs, induce liquid-phase separation of Rubisco into minimal pyrenoids with functional CCMs. Using ancestral sequence reconstruction, we trace the evolution of pyrenoids and demonstrate that selection acted on carboxylation rate, and in selected cases on specificity, providing unexpected perspectives on the design and function of natural and synthetic pyrenoids.

biochemistry↗

bioRxiv2024

Advancing chloroplast synthetic biology through high-throughput plastome engineering of Chlamydomonas reinhardtii

Chloroplast synthetic biology holds promise for developing improved crops through improving the function of plastids. However, chloroplast engineering efforts face limitations due to the scarcity of genetic tools and the low throughput of plant-based systems. To address these challenges, we here established Chlamydomonas reinhardtii as a prototyping chassis for chloroplast synthetic biology. We developed an automation workflow that enables the generation, handling, and analysis of thousands of transplastomic strains in parallel, expanded the repertoire of selection markers for chloroplast transformation, established new reporter genes, and characterized over 140 regulatory parts, including native and synthetic promoters, UTRs, and intercistronic expression elements. We integrated the system within the Phytobrick cloning standard and demonstrate several applications, including a library-based approach to develop synthetic promoter designs in plastids. Finally, we provide a proof-of-concept for prototyping novel traits in plastids by introducing a chloroplast-based synthetic photorespiration pathway and demonstrating a twofold increase in biomass production. Overall, our study advances chloroplast engineering, and provides a promising platform to rapidly prototype chloroplast manipulations before their transfer into higher plants and crops.

synthetic biology↗

bioRxiv2024

In vitro transcription-based biosensing of glycolate for prototyping of a complex enzyme cascade

In vitro metabolic systems allow the reconstitution of natural and new-to-nature pathways outside of their cellular context and are of increasing interest in bottom-up synthetic biology, cell-free manufacturing and metabolic engineering. Yet, the prototyping of such in vitro networks is very often restricted by time- and cost-intensive analytical methods. To overcome these limitations, we sought to develop an in vitro transcription (IVT)-based biosensing workflow that offers fast results at low-cost, minimal volumes and high-throughput. As a proof-of-concept, we present an IVT biosensor for the so-called CETCH cycle, a complex in vitro metabolic system that converts CO2 into glycolate. To quantify glycolate production, we constructed a sensor module that is based on the glycolate repressor GlcR from Paracoccus denitrificans, and established an IVT biosensing off-line workflow that allows to measure glycolate from CETCH samples from the {micro}M to mM range. We characterized the influence of different cofactors on IVT output and further optimized our IVT biosensor against varying sample conditions. We show that availability of free Mg2+ is a critical factor in IVT biosensing and that IVT output is heavily influenced by ATP, NADPH and other phosphorylated metabolites frequently used in in vitro systems. Our final biosensor is highly robust and shows an excellent correlation between IVT output and classical LC-MS quantification, but notably at [~]10-fold lowered cost and [~]10 times faster turnover time. Our results demonstrate the potential of IVT-based biosensor systems to break current limitations in biological design-build-test cycles for the prototyping of individual enzymes, complex reaction cascades and in vitro metabolic networks.

synthetic biology↗

bioRxiv2024

Multiple levels of transcriptional regulation control glycolate metabolism in Paracoccus denitrificans

The hydroxyacid glycolate is a highly abundant carbon source in the environment. Glycolate is produced by unicellular photosynthetic organisms and excreted at petagram scales to the environment, where it serves as growth substrate for heterotrophic bacteria. In microbial metabolism, glycolate is first oxidized to glyoxylate by the enzyme glycolate oxidase. The recently described {beta}-hydroxyaspartate cycle (BHAC) subsequently mediates the carbon-neutral assimilation of glyoxylate into central metabolism in ubiquitous Alpha- and Gammaproteobacteria. While the reaction sequence of the BHAC was elucidated in Paracoccus denitrificans, little is known about the regulation of glycolate and glyoxylate assimilation in this relevant alphaproteobacterial model organism. Here, we show that regulation of glycolate metabolism in P. denitrificans is surprisingly complex, involving two regulators, the IclR-type transcription factor BhcR that acts as an activator for the BHAC gene cluster, as well as the GntR-type transcriptional regulator GlcR, a previously unidentified repressor that controls the production of glycolate oxidase. Furthermore, an additional layer of regulation is exerted at the global level, which involves the transcriptional regulator CceR that controls the switch between glycolysis and gluconeogenesis in P. denitrificans. Together, these regulators control glycolate metabolism in P. denitrificans, allowing the organism to assimilate glycolate together with other carbon substrates in a simultaneous fashion, rather than sequentially. Our results show that the metabolic network of Alphaproteobacteria shows a high degree of flexibility to react to the availability of multiple substrates in the environment.

microbiology↗

bioRxiv2024

Layered entrenchment maintains essentiality in protein-protein interactions.

Protein complexes composed of strictly essential subunits are abundant in nature and arise through the gradual complexification of ancestral precursor proteins followed by their co-evolution with the newly recruited components. Essentiality arises during co-evolution by the accumulation of changes that are tolerated in the complex state but would be deleterious for the standalone complex components. While this theoretical framework to explain how essentiality arises has been proposed long ago, it is unclear which factors cause essentiality to persist over evolutionary timescales. In this work we show that the central enzyme of photosynthesis, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), rapidly started to depend on a newly recruited interaction partner through multiple, genetically distinct mechanisms that affect stability, solubility, and catalysis. We further demonstrate that layering multiple mechanisms of essentiality can lead to the persistence of essentiality, even if any given mechanism reverts through chance or selection. More broadly, our work highlights that new interaction partners can drastically re-shape which substitutions are tolerated in the proteins they are recruited into. This can lead to the rapid evolution of multi-layered essentiality through the exploration of areas of sequence space that are only accessible in the complex state.

biochemistry↗