Showing papers by "Andrew D. Ellington published in 2022"
TL;DR: The results demonstrate a viable route for enzymatic plastic recycling at the industrial scale and a closed-loop PET recycling process by using FAST-PETase and resynthesizing PET from the recovered monomers.
222 citations
TL;DR: In this article , the authors characterized the molecular effects of the Omicron spike mutations on expression, ACE2 receptor affinity, and neutralizing antibody recognition of the SARS-CoV-2.
24 citations
TL;DR: In this paper , a combined screening and selection approach was developed to refine the affinities and specificities of generalist transcription factors; using RamR as a starting point, they evolve highly specific (>100-fold preference) and sensitive (half-maximum effective concentration (EC50) < 30 μM) biosensors for the alkaloids tetrahydropapaverine, papaverine and noscapine.
Abstract: A key bottleneck in the microbial production of therapeutic plant metabolites is identifying enzymes that can improve yield. The facile identification of genetically encoded biosensors can overcome this limitation and become part of a general method for engineering scaled production. We have developed a combined screening and selection approach that quickly refines the affinities and specificities of generalist transcription factors; using RamR as a starting point, we evolve highly specific (>100-fold preference) and sensitive (half-maximum effective concentration (EC50) < 30 μM) biosensors for the alkaloids tetrahydropapaverine, papaverine, glaucine, rotundine and noscapine. High-resolution structures reveal multiple evolutionary avenues for the malleable effector-binding site and the creation of new pockets for different chemical moieties. These sensors further enabled the evolution of a streamlined pathway for tetrahydropapaverine, a precursor to four modern pharmaceuticals, collapsing multiple methylation steps into a single evolved enzyme. Our methods for evolving biosensors enable the rapid engineering of pathways for therapeutic alkaloids. A combined screening and selection approach enables the evolution of the generalist transcription factor RamR into specific and sensitive biosensors for various alkaloids and in turn a streamlined pathway for tetrahydropapaverine biosynthesis.
23 citations
TL;DR: In this article , a panel of three mutually orthogonal promoters that can be acted on by artificial gRNAs bound by CRISPR regulators were designed, and guide RNA expression targeting these promoters was in turn controlled by either Pol III (U6) or ethylene-inducible Pol II promoters, implementing for the first time a fully artificial Orthogonal Control System (OCS).
Abstract: The construction and application of synthetic genetic circuits is frequently improved if gene expression can be orthogonally controlled, relative to the host. In plants, orthogonality can be achieved via the use of CRISPR-based transcription factors that are programmed to act on natural or synthetic promoters. The construction of complex gene circuits can require multiple, orthogonal regulatory interactions, and this in turn requires that the full programmability of CRISPR elements be adapted to non-natural and non-standard promoters that have few constraints on their design. Therefore, we have developed synthetic promoter elements in which regions upstream of the minimal 35S CaMV promoter are designed from scratch to interact via programmed gRNAs with dCas9 fusions that allow activation of gene expression.A panel of three, mutually orthogonal promoters that can be acted on by artificial gRNAs bound by CRISPR regulators were designed. Guide RNA expression targeting these promoters was in turn controlled by either Pol III (U6) or ethylene-inducible Pol II promoters, implementing for the first time a fully artificial Orthogonal Control System (OCS). Following demonstration of the complete orthogonality of the designs, the OCS was tied to cellular metabolism by putting gRNA expression under the control of an endogenous plant signaling molecule, ethylene. The ability to form complex circuitry was demonstrated via the ethylene-driven, ratiometric expression of fluorescent proteins in single plants.The design of synthetic promoters is highly generalizable to large tracts of sequence space, allowing Orthogonal Control Systems of increasing complexity to potentially be generated at will. The ability to tie in several different basal features of plant molecular biology (Pol II and Pol III promoters, ethylene regulation) to the OCS demonstrates multiple opportunities for engineering at the system level. Moreover, given the fungibility of the core 35S CaMV promoter elements, the derived synthetic promoters can potentially be utilized across a variety of plant species.
10 citations
TL;DR: GroovDB (available at https://groov.bio), a Web-accessible database of ligand-inducible transcription factors that contains all information necessary to build chemically-responsive genetic circuits, including biosensor sequence, ligand, and operator data is developed.
Abstract: Genetic biosensors are integral to synthetic biology. In particular, ligand-inducible prokaryotic transcription factors are frequently used in high-throughput screening, for dynamic feedback regulation, as multi-layer logic gates, and in diagnostic applications. In order to provide a curated source that users can rely on for engineering applications, we have developed GroovDB (available at https://groov.bio), a Web-accessible database of ligand-inducible transcription factors that contains all information necessary to build chemically-responsive genetic circuits, including biosensor sequence, ligand, and operator data. Ligand and DNA interaction data has been verified against the literature, while an automated data curation pipeline is used to programmatically fetch metadata, structural information, and references for every entry. A custom tool to visualize the natural genetic context of biosensor entries provides additional information that provides potential insights into alternative ligands and systems biology.
7 citations
TL;DR: The development of a modular fusion domain whose charged surface can be modified at will should prove to be of use in the engineering of other polymerases and, in general, may prove useful for protein stabilization.
Abstract: The charge states of proteins can greatly influence their stabilities and interactions with substrates, and the addition of multiple charges (supercharging) has been shown to be a successful approach for engineering protein stability and function. The addition of a fast-folding fusion domain to the Bacillus stearothermophilus DNA polymerase improved its functionality in isothermal amplification assays, and further charge engineering of this domain has increased both protein stability and diagnostics performance. When combined with mutations that stabilize the core of the protein, the charge-engineered fusion domain leads to the ability to carry out loop-mediated isothermal amplification (LAMP) at temperatures up to 74° C or in the presence of high concentrations of urea, with detection times under 10 min. Adding both positive and negative charges to the fusion domain led to changes in the relative reverse transcriptase and DNA polymerase activities of the polymerase. Overall, the development of a modular fusion domain whose charged surface can be modified at will should prove to be of use in the engineering of other polymerases and, in general, may prove useful for protein stabilization.
7 citations
TL;DR: The ribosome is a macromolecular machine that catalyzes the sequence-defined polymerization of L-α-amino acids into polypeptides as discussed by the authors .
Abstract: Abstract The ribosome is a macromolecular machine that catalyzes the sequence-defined polymerization of L-α-amino acids into polypeptides. The catalysis of peptide bond formation between amino acid substrates is based on entropy trapping, wherein the adjacency of transfer RNA (tRNA)-coupled acyl bonds in the P-site and the α-amino groups in the A-site aligns the substrates for coupling. The plasticity of this catalytic mechanism has been observed in both remnants of the evolution of the genetic code and modern efforts to reprogram the genetic code (e.g., ribosomal incorporation of non-canonical amino acids, ribosomal ester formation). However, the limits of ribosome-mediated polymerization are underexplored. Here, rather than peptide bonds, we demonstrate ribosome-mediated polymerization of pyridazinone bonds via a cyclocondensation reaction between activated γ-keto and α-hydrazino ester monomers. In addition, we demonstrate the ribosome-catalyzed synthesis of peptide-hybrid oligomers composed of multiple sequence-defined alternating pyridazinone linkages. Our results highlight the plasticity of the ribosome’s ancient bond-formation mechanism, expand the range of non-canonical polymeric backbones that can be synthesized by the ribosome, and open the door to new applications in synthetic biology.
4 citations
TL;DR: In this article , a strain of Shewanella oneidensis that heterologously expressed abundant, conductive Geobacter pili when grown aerobically in liquid culture was designed to scale the production of conductive pili.
4 citations
TL;DR:
Abstract: Protein reagents are indispensable for most molecular and synthetic biology procedures. Most conventional protocols rely on highly purified protein reagents that require considerable expertise, time, and infrastructure to produce. In consequence, most proteins are acquired from commercial sources, reagent expense is often high, and accessibility may be hampered by shipping delays, customs barriers, geopolitical constraints, and the need for a constant cold chain. Such limitations to the widespread availability of protein reagents, in turn, limit the expansion and adoption of molecular biology methods in research, education, and technology development and application. Here, we describe protocols for producing a low‐resource and locally sustainable reagent delivery system, termed “cellular reagents,” in which bacteria engineered to overexpress proteins of interest are dried and can then be used directly as reagent packets in numerous molecular biology reactions, without the need for protein purification or a constant cold chain. As an example of their application, we describe the execution of polymerase chain reaction (PCR) and loop‐mediated isothermal amplification (LAMP) using cellular reagents, detailing how to replace pure protein reagents with optimal amounts of rehydrated cellular reagents. We additionally describe a do‐it‐yourself fluorescence visualization device for using these cellular reagents in common molecular biology applications. The methods presented in this article can be used for low‐cost, on‐site production of commonly used molecular biology reagents (including DNA and RNA polymerases, reverse transcriptases, and ligases) with minimal instrumentation and expertise, and without the need for protein purification. Consequently, these methods should generally make molecular biology reagents more affordable and accessible. © 2022 Wiley Periodicals LLC.
4 citations
TL;DR: Considerations are described and suggestions for enhancing security in the publication of synthetic biology research and techniques to build and support a safe and secure research enterprise that is able to maximize its positive impacts and minimize any negative outcomes.
Abstract: The ability to construct, synthesize, and edit genes and genomes at scale and with speed enables, in synergy with other tools of engineering biology, breakthrough applications with far-reaching implications for society. As SARS-CoV-2 spread around the world in early spring of 2020, researchers rapidly mobilized, using these tools in the development of diagnostics, therapeutics, and vaccines for COVID-19. The sharing of knowledge was crucial to making rapid progress. Several publications described the use of reverse genetics for the de novo construction of SARS-CoV-2 in the laboratory, one in the form of a protocol. Given the demonstrable harm caused by the virus, the unequal distribution of mitigating vaccines and therapeutics, their unknown efficacy against variants, and the interest in this research by laboratories unaccustomed to working with highly transmissible pandemic pathogens, there are risks associated with such publications, particularly as protocols. We describe considerations and offer suggestions for enhancing security in the publication of synthetic biology research and techniques. We recommend: (1) that protocol manuscripts for the de novo synthesis of certain pathogenic viruses undergo a mandatory safety and security review; (2) that if published, such papers include descriptions of the discussions or review processes that occurred regarding security considerations in the main text; and (3) the development of a governance framework for the inclusion of basic security screening during the publication process of engineering biology/synthetic biology manuscripts to build and support a safe and secure research enterprise that is able to maximize its positive impacts and minimize any negative outcomes.
4 citations
TL;DR: Two isothermal nucleic acid amplification assays for detection of monkeypox virus (MPXV) clades 2 and 3 that include the strains responsible for the current global outbreak ofmonkeypox are reported, which could readily detect single digit copies of MPXV synthetic double stranded DNA templates within 30 min.
Abstract: We report two isothermal nucleic acid amplification assays for detection of monkeypox virus (MPXV) clades 2 and 3 that include the strains responsible for the current global outbreak of monkeypox. The assays use loop-mediated isothermal amplification (LAMP) to amplify two distinct sequences in the MPXV genome. Readout specificity is ensured by oligonucleotide strand displacement (OSD) probes integrated in one-pot LAMP-OSD reactions. OSD probes undergo toehold-mediated strand displacement hybridization to LAMP amplicon loop sequences derived from MPXV clades 2 and 3 resulting in fluorescence readable both in real-time and visually at endpoint. We also perform both assays on two different portable devices, the GeneTiger and the miniPCR, to exemplify compatibility with minimum infrastructure point-of-care (POC) testing in clinical and at-home settings. Both assays could readily detect single digit copies of MPXV synthetic double stranded DNA templates within 30 min.
TL;DR: A combined approach exploiting the benefits of both top-down and bottom-up mass spectrometry was developed, allowing high quality characterization, localization of diselenide bridges for complex proteins, and the identification of previously unreported selenoprotein dimers.
Abstract: With the rapid acceleration in the design and development of new biotherapeutics, ensuring consistent quality and understanding degradation pathways remain paramount, requiring an array of analytical methods including mass spectrometry. The incorporation of non-canonical amino acids, such as for synthetic selenoproteins, creates additional challenges. A comprehensive strategy to characterize selenoproteins should serve dual purposes of providing sequence confirmation and mapping of selenocysteine bridge locations and the identification of unanticipated side products. In the present study, a combined approach exploiting the benefits of both top-down and bottom-up mass spectrometry was developed. Both electron-transfer/higher-energy collision dissociation and 213 nm ultraviolet photodissociation were utilized to provide complementary information, allowing high quality characterization, localization of diselenide bridges for complex proteins, and the identification of previously unreported selenoprotein dimers.
TL;DR: An enzyme that relies on a fully functional proofreading domain to correct mismatches on DNA, RNA, and 2'-O-methyl templates is evolved and a downstream analysis strategy is implemented that accommodates deletions that arise during phosphoramidite synthesis, the most common type of synthesis error.
Abstract: DNA is increasingly being explored as an alternative medium for digital information storage, but the potential information loss from degradation and associated issues with error during reading challenge its wide-scale implementation. To address this, we propose an atomic-scale encoding standard for DNA, where information is encoded in degradation-resistant analogues of natural nucleic acids (xNAs). To better enable this approach, we used directed evolution to create a polymerase capable of transforming 2'-O-methyl templates into double-stranded DNA. Starting from a thermophilic, error-correcting reverse transcriptase, RTX, we evolved an enzyme (RTX-Ome v6) that relies on a fully functional proofreading domain to correct mismatches on DNA, RNA, and 2'-O-methyl templates. In addition, we implemented a downstream analysis strategy that accommodates deletions that arise during phosphoramidite synthesis, the most common type of synthesis error. By coupling and integrating new chemistries, enzymes, and algorithms, we further enable the large-scale use of nucleic acids for information storage.
TL;DR: In this paper , the authors characterize the kinetics of the elementary steps in LAMP and show that strand invasion / initiation is the rate-limiting step in the LAMP reaction and the loop primer plays an important role in accelerating the rate of initiation.
Abstract: Abstract Loop-mediated isothermal amplification (LAMP) has proven to be easier to implement than PCR for point-of-care diagnostic tests. However, the underlying mechanism of LAMP is complicated and the kinetics of the major steps in LAMP have not been fully elucidated, which prevents rational improvements in assay development. Here we present our work to characterize the kinetics of the elementary steps in LAMP and show that: (i) strand invasion / initiation is the rate-limiting step in the LAMP reaction; (ii) the loop primer plays an important role in accelerating the rate of initiation and does not function solely during the exponential amplification phase and (iii) strand displacement synthesis by Bst-LF polymerase is relatively fast (125 nt/s) and processive on both linear and hairpin templates, although with some interruptions on high GC content templates. Building on these data, we were able to develop a kinetic model that relates the individual kinetic experiments to the bulk LAMP reaction. The assays developed here provide important insights into the mechanism of LAMP, and the overall model should be crucial in engineering more sensitive and faster LAMP reactions. The kinetic methods we employ should likely prove useful with other isothermal DNA amplification methods.
01 Jan 2022
TL;DR: A review of the most successful engineered RNP systems and their applications can be found in this article , where the authors provide a streamlined method for identifying an RNP control system most useful to their own work.
Abstract: Ribonucleoproteins (RNPs) are RNA-protein complexes utilized natively in both prokaryotes and eukaryotes to regulate essential processes within the cell. Over the past few years, many of these native systems have been adapted to provide control over custom genetic targets. Engineered RNP-based control systems allow for fine-tune regulation of desired targets, by providing customizable nucleotide-nucleotide interactions. However, as there have been several engineered RNP systems developed recently, identifying an optimal system for various bioprocesses is challenging. Here, we review the most successful engineered RNP systems and their applications to survey the current state of the field. Additionally, we provide selection criteria to provide users a streamlined method for identifying an RNP control system most useful to their own work. Lastly, we discuss future applications of RNP control systems and how they can be utilized to address the current grand challenges of the synthetic biology community.
TL;DR: It is shown for the first time that Engineering the N-terminus of CB1R allows for efficient signal transduction in yeast, and that engineering the sterol composition of the yeast membrane optimizes CB2R performance.
Abstract: Yeast expression of human G Protein Coupled Receptors (GPCRs) can be used as a biosensor platform for the detection of pharmaceuticals. The Cannabinoid receptors type 1 and 2 (CB1/2R) are of particular interest, given the cornucopia of natural and synthetic cannabinoids being explored as therapeutics. We show for the first time that engineering the N-terminus of CB1R allows for efficient signal transduction in yeast, and that engineering the sterol composition of the yeast membrane optimizes CB2R performance. Using the dual cannabinoid biosensors, large libraries of synthetic cannabinoids and terpenes could be quickly screened to elucidate known and novel structure-activity relationships, including compounds and trends that more selectively target each of the two receptors. The biosensor strains offer a ready platform for evaluating the activity of new synthetic cannabinoids, monitoring drugs of abuse, and developing molecules that target the therapeutically important CB2R receptor while minimizing psychoactive effects.
TL;DR: This work uses strand displacement reactions to algorithmically modify data stored in the topological modification of DNA to set the foundation of entirely molecular algorithms for parallel manipulation of digital information kept in DNA.
Abstract: DNA is an incredibly dense storage medium for digital data, but computing on the stored information is expensive and slow (rounds of sequencing, in silico computation, and DNA synthesis). Augmenting DNA storage with “in-memory” molecular computation, we use strand displacement reactions to algorithmically modify data stored in the topological modification of DNA. A secondary sequence-level encoding allows high-throughput sequencing-based readout. We show multiple rounds of binary counting and cellular automaton Rule 110 computation on 4-bit data registers, as well as selective access and erasure. Avoiding stringent sequence design, we demonstrate large strand displacement cascades (122 distinct steps) on naturally-occurring DNA sequences. Our work merges DNA storage and DNA computing, setting the foundation of entirely molecular algorithms for parallel manipulation of digital information kept in DNA.
TL;DR: The utility of dye-based, high-resolution melting (HRM) as an alternative to UV-Vis determinations of hyperchromicity in order to more quickly acquire parameters for duplex stability prediction is assessed and it is found that hybridization stability could be predicted as a function of sequence and backbone composition for a variety of duplexes.
Abstract: The ability to predict nucleic acid hybridization energies has been greatly enabling for many applications, but predictive models require painstaking experimentation, which may limit expansion to non-natural nucleic acid analogues and chemistries. We have assessed the utility of dye-based, high-resolution melting (HRM) as an alternative to UV-Vis determinations of hyperchromicity in order to more quickly acquire parameters for duplex stability prediction. The HRM-derived model for phosphodiester (PO) DNA can make comparable predictions to previously established models. Using HRM, it proved possible to develop predictive models for DNA duplexes containing phosphorothioate (PS) linkages, and we found that hybridization stability could be predicted as a function of sequence and backbone composition for a variety of duplexes, including PS:PS, PS:PO, and partially modified backbones. Individual phosphorothioate modifications destabilize helices by around 0.12 kcal/mol on average. Finally, we applied these models to the design of a catalytic hairpin assembly circuit, an enzyme-free amplification method used for nucleic acid-based molecular detection. Changes in PS circuit behavior were consistent with model predictions, further supporting the addition of HRM modeling and parameters for PS oligonucleotides to the rational design of nucleic acid hybridization.
TL;DR: In this article , the TetR family repressor RolR that is responsive to the related compound resorcinol was employed to identify variants that had greatly improved activities with phloroglucinol.
Abstract: Biosensors can accelerate the engineering of new biosynthetic pathways. Phloroglucinol is a platform chemical of wide utility that can be produced at limited titers in Escherichia coli. Starting from the TetR family repressor RolR that is responsive to the related compound resorcinol, we were able to employ a combined selection and screen to identify variants that had greatly improved activities with phloroglucinol (EC50 for phloroglucinol of 131 uM, relative to an estimated 42 mM for wild-type RolR). The variants obtained were further screened with a panel of similar single ring aromatics, and several were found to be generalists, consistent with the hypothesis that both natural and directed evolution tend to first create semi-specific pockets prior to further optimization for new function
TL;DR: Graphene biosensor technology is demonstrated, based on liquid-gated graphene field-effect transistors, for rapid and ultraprecise detection and differentiation of influenza and SARS-CoV-2 surface protein, which has a fast response time of ~10 seconds enabling rapid diagnosis.
Abstract: The SARS-CoV-2 pandemic has highlighted the need for devices capable of carrying out rapid differential detection of viruses that may manifest similar physiological symptoms yet demand tailored treatment plans. Seasonal influenza may be exacerbated by COVID-19 infections, increasing the burden on healthcare systems. In this work, we demonstrate a technology, based on liquid-gated graphene field-effect transistors, for rapid and ultraprecise detection and differentiation of influenza and SARS-CoV-2 surface protein. The device consists of 4 onboard graphene field-effect electrolyte-gated transistors arranged in a quadruple architecture, where each quarter is functionalized with either antigen-specific antibody or chemically passivated control. The antigen-antibody interaction is dependent on uniform diffusion of virus delivered in low ionic strength phosphate buffer solution, entailing a facile operating procedure, where the user adds a drop of the viral surface protein solution onto the device. Our sensor platform was tested against a range of concentrations of viral surface proteins from both viruses with the lowest tested and detected concentration at ~50 ag/mL, or 88 zM for COVID-19 and 227 zM for Flu, 5-fold lower than the values reported previously on a similar platform. Unlike the contemporary standard, RT-PCR test, which have a turnaround time of a few hours, the reported graphene biosensor technology has a fast response time of ~10 seconds enabling rapid diagnosis. Furthermore, the antibodies tested were confirmed to be antigen-specific through cross-reactivity tests. Thus, we have developed a multi-virus, highly sensitive and specific detection tool for rapid diagnostic applications for contemporary, emerging, and future viruses.