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Rxivist combines preprints from bioRxiv with data from Twitter to help you find the papers being discussed in your field. Currently indexing 65,106 bioRxiv papers from 288,545 authors.

Most downloaded bioRxiv papers, all time

in category synthetic biology

607 results found. For more information, click each entry to expand.

41: Selection of chromosomal DNA libraries using a multiplex CRISPR system in Saccharomyces cerevisiae
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Posted to bioRxiv 21 Jul 2014

Selection of chromosomal DNA libraries using a multiplex CRISPR system in Saccharomyces cerevisiae
2,021 downloads synthetic biology

Owen W Ryan, Jeffrey M Skerker, Matthew J Maurer, Xin Li, Jordan C Tsai, Snigdha Poddar, Michael E Lee, Will DeLoache, John E Dueber, Adam P Arkin, Jamie H D Cate

The directed evolution of biomolecules to improve or change their activity is central to many engineering and synthetic biology efforts. However, selecting improved variants from gene libraries in living cells requires plasmid expression systems that suffer from variable copy number effects, or the use of complex marker-dependent chromosomal integration strategies. We developed quantitative gene assembly and DNA library insertion into the Saccharomyces cerevisiae genome by optimizing an efficient single-step and marker-free genome editing system using CRISPR-Cas9. With this Multiplex CRISPR (CRISPRm) system, we selected an improved cellobiose utilization pathway in diploid yeast in a single round of mutagenesis and selection, which increased cellobiose fermentation rates by over ten-fold. Mutations recovered in the best cellodextrin transporters reveal synergy between substrate binding and transporter dynamics, and demonstrate the power of CRISPRm to accelerate selection experiments and discoveries of the molecular determinants that enhance biomolecule function.

42: Gene cloning and construction of prokaryotic and plant expression vectors of RICIN-A-Chain/PAP-S1 fusion protein and its inhibition of protein synthesis
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Posted to bioRxiv 28 Mar 2016

Gene cloning and construction of prokaryotic and plant expression vectors of RICIN-A-Chain/PAP-S1 fusion protein and its inhibition of protein synthesis
2,012 downloads synthetic biology

Yasser S. Hassan, Sherry L. Ogg

Pokeweed antiviral protein (PAP) is a single-chain ribosome-inactivating protein that exists in several forms isolated from various organs and at different stages of development of Phytolacca americana (pokeweed). In this study, PAP-S1, one of the two known isoforms found in seeds, was isolated and PCR amplified using primers based on the known mRNA of PAP-S2, the other known form found in seeds. The complete cDNA encoding PAP-S1 was determined here for the first time. PAP-S1 is a potent antiviral protein with many potential clinical applications. However, it was found to be dosage dependent with observed side effects at high dosage. In this study, we report the production of a recombinant antiviral peptide-fusion protein between Ricin A-chain and PAP-S1. The peptide-fusion recombinant proteins Ricin-A-Chain/PAP-S1 and PAP-S1/Ricin-A-Chain were generated by joining the N-terminus of PAP-S1 to the C-terminus of Ricin A-chain and the C-terminus of PAP-S1 to the N-terminus of Ricin A-chain respectively, and were expressed in an Escherichia coli cell free expression systems. The peptide-fusion recombinant protein Ricin-A-Chain/PAP-S1 (F2) was found to be more active than the PAP-S1/Ricin-A-chain (F1) and similar to PAP-S1 in a cell free prokaryotic environment, and both showed much stronger activity in a cell free eukaryotic environment. The DNA sequence of the complete cDNA of PAP-S1 and of the peptide-fusion protein Ricin-A-Chain/PAP-S1 with the PAP-S1 signal peptide at the N-terminus of Ricin A-chain were inserted in plant destination binary vectors for A. tumefaciens mediated transformation. It is the opinion of the authors that additional research should be done in order to determine both cytotoxicity and selectivity of fusion protein F2 compared to PAP-S1, as it could be a viable, more potent and less cytotoxic alternative to PAP-S1 alone at high dosage, for both agricultural and therapeutic applications.

43: Daisy quorum drives for the genetic restoration of wild populations
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Posted to bioRxiv 10 Mar 2017

Daisy quorum drives for the genetic restoration of wild populations
1,949 downloads synthetic biology

John Min, Charleston Noble, Devora Najjar, Kevin M Esvelt

An ideal gene drive system to alter wild populations would 1) exclusively affect organisms within the political boundaries of consenting communities, and 2) be capable of restoring any engineered population to its original genetic state. Here we describe ‘daisy quorum’ drive systems that meet these criteria by combining daisy drive with underdominance. A daisy quorum drive system is predicted to spread through a population until all of its daisy elements have been lost, at which point its fitness becomes frequency-dependent: mostly altered populations become fixed for the desired change, while engineered genes at low frequency are swiftly eliminated by natural selection. The result is an engineered population surrounded by wild-type organisms with limited mixing at the boundary. Releasing large numbers of wild-type organisms or a few bearing a population suppression element can reduce the engineered population below the quorum, triggering elimination of all engineered sequences. In principle, the technology can restore any drive-amenable population carrying introduced genes from any source to wild-type genetics. Daisy quorum systems may enable efficient, community-supported, and genetically reversible ecological engineering.

44: Low cost and open source multi-fluorescence imaging system for teaching and research in biology and bioengineering
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Posted to bioRxiv 27 Sep 2017

Low cost and open source multi-fluorescence imaging system for teaching and research in biology and bioengineering
1,877 downloads synthetic biology

Nuñez Isaac, Matute Tamara, Herrera Roberto, Keymer Juan, Marzullo Tim, Rudge Tim, Federici Fernán

The advent of easy-to-use open source microcontrollers, off-the-shelf electronics and customizable manufacturing technologies has facilitated the development of inexpensive scientific devices and laboratory equipment. In this study, we describe an imaging system that integrates low-cost and open-source hardware, software and genetic resources. The multi-fluorescence imaging system consists of readily available 470 nm LEDs, a Raspberry Pi camera and a set of filters made with low cost acrylics. This device allows imaging in scales ranging from single colonies to entire plates. We developed a set of genetic components (e.g. promoters, coding sequences, terminators) and vectors following the standard framework of Golden Gate, which allowed the fabrication of genetic constructs in a combinatorial, low cost and robust manner. In order to provide simultaneous imaging of multiple wavelength signals, we screened a series of long stokes shift fluorescent proteins that could be combined with cyan/green fluorescent proteins. We found CyOFP1, mBeRFP and sfGFP to be the most compatible set for 3-channel fluorescent imaging. We developed open source Python code to operate the hardware to run time-lapse experiments with automated control of illumination and camera and a Python module to analyze data and extract meaningful biological information. To demonstrate the potential application of this integral system, we tested its performance on a diverse range of imaging assays often used in disciplines such as microbial ecology, microbiology and synthetic biology. We also assessed its potential for STEM teaching in a high school environment, using it to teach biology, hardware design, optics, and programming. Together, these results demonstrate the successful integration of open source hardware, software, genetic resources and customizable manufacturing to obtain a powerful, low cost and robust system for STEM education, scientific research and bioengineering. All the resources developed here are available under open source licenses.

45: Deep Learning Of The Regulatory Grammar Of Yeast 5′ Untranslated Regions From 500,000 Random Sequences
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Posted to bioRxiv 12 May 2017

Deep Learning Of The Regulatory Grammar Of Yeast 5′ Untranslated Regions From 500,000 Random Sequences
1,856 downloads synthetic biology

Josh T. Cuperus, Benjamin Groves, Anna Kuchina, Alexander B Rosenberg, Nebojsa Jojic, Stanley Fields, Georg Seelig

Our ability to predict protein expression from DNA sequence alone remains poor, reflecting our limited understanding of cis-regulatory grammar and hampering the design of engineered genes for synthetic biology applications. Here, we generate a model that predicts the translational efficiency of the 5′ untranslated region (UTR) of mRNAs in the yeast Saccharomyces cerevisiae. We constructed a library of half a million 50-nucleotide-long random 5′ UTRs and assayed their activity in a massively parallel growth selection experiment. The resulting data allow us to quantify the impact on translation of Kozak sequence composition, upstream open reading frames (uORFs) and secondary structure. We trained a convolutional neural network (CNN) on the random library and showed that it performs well at predicting the translational efficiency of both a held-out set of the random 5′ UTRs as well as native S. cerevisiae 5′ UTRs. The model additionally was used to computationally evolve highly translating 5′ UTRs. We confirmed experimentally that the great majority of the evolved sequences lead to higher translation rates than the starting sequences, demonstrating the predictive power of this model.

46: Engineered Cpf1 Enzymes with Altered PAM Specificities
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Posted to bioRxiv 04 Dec 2016

Engineered Cpf1 Enzymes with Altered PAM Specificities
1,827 downloads synthetic biology

Linyi Gao, David B.T. Cox, Winston X Yan, John Manteiga, Martin Schneider, Takashi Yamano, Hiroshi Nishimasu, Osamu Nureki, Feng Zhang

The RNA-guided endonuclease Cpf1 is a promising tool for genome editing in eukaryotic cells. Compared to other genome editing platforms, Cpf1 offers distinct advantages, such as the ability to easily target multiple genes simultaneously, as well as low rates of off-target activity. However, the Acidaminococcus sp. BV3L6 Cpf1 (AsCpf1), which has been successfully harnessed for genome editing, can only robustly cleave target sites preceded by a TTTV protospacer adjacent motif (PAM), which may limit its practical utility. To address this limitation, we used a structure- guided saturation mutagenesis screen to increase the targeting range of Cpf1. We engineered two variants of AsCpf1 with the mutations S542R/K607R and S542R/K548V/N552R that can cleave target sites with TYCV/CCCC and TATV PAMs, respectively, with enhanced activities in vitro and in human cells. Genome-wide assessment of off-target activity indicated that these variants retain a high level of DNA targeting specificity, which can be further improved by introducing mutations in non-PAM-interacting domains. Together, these variants increase the targeting range of AsCpf1 to one cleavage site for every ~8.7 bp in non-repetitive regions of the human genome, providing a useful addition to the CRISPR/Cas genome engineering toolbox.

47: Quantifying cellular capacity to identify gene expression designs with reduced burden
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Posted to bioRxiv 22 Dec 2014

Quantifying cellular capacity to identify gene expression designs with reduced burden
1,820 downloads synthetic biology

Francesca Ceroni, Rhys Algar, Guy-Bart Stan, Tom Ellis

Heterologous gene expression can be a significant burden to cells, consuming resources and causing decreased growth and stability. We describe here an in vivo monitor that tracks E. coli capacity changes in real-time and can be used to assay the burden synthetic constructs and their parts impose. By measuring capacity, construct designs with reduced burden can be identified and shown to predictably outperform less efficient designs, despite having equivalent expression outputs.

48: The WPRE Improves Genetic Engineering With Site-Specific Nucleases
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Posted to bioRxiv 12 Apr 2017

The WPRE Improves Genetic Engineering With Site-Specific Nucleases
1,756 downloads synthetic biology

Jessica M. Ong, Christopher R Brown, Matthew C. Mendel, Gregory J Cost

Inclusion of the woodchuck hepatitis virus post-transcriptional response element (WPRE) in the 3′ UTR of mRNA encoding zinc-finger or TALE nucleases results in up to a fifty-fold increase in nuclease expression and a several-fold increase in nuclease-modified chromosomes. Significantly, this increase is additive with the enhancement generated by transient hypothermic shock. The WPRE-mediated improvement is seen across several types of human and mouse primary and transformed cells and is translatable in vivo to the mouse liver.

49: Histone modifications and active gene expression are associated with enhanced CRISPR activity in de-silenced chromatin
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Posted to bioRxiv 04 Dec 2017

Histone modifications and active gene expression are associated with enhanced CRISPR activity in de-silenced chromatin
1,742 downloads synthetic biology

René Daer, Cassandra M Barrett, Karmella A Haynes

Recently we demonstrated that closed chromatin composed of Polycomb proteins and histone 3 lysine 27 trimethylation impedes CRISPR-mediated genome editing by blocking the accessibility of chromosomal DNA to spCas9/sgRNA. Editing efficiencies were higher in cells where the same reporter locus had not been repressed, thus we presume that silenced chromatin can be modified to generate a Cas9-accessible state. To test this idea, we exposed the locus to antagonists of Polycomb silencing: Gal4-p65, a targeted transcriptional activator, and UNC1999, a chemical inhibitor of the histone H3K27 methyltransferase EZH2. For both we observed loss of histone trimethylation. Only Gal4-p65 treatment increased target gene expression. Initial Gal4-p65 overexpression impedes Cas9 activity, while a 9-day recovery period leads to enhanced Cas9 efficiency up to 1000 bp from the Gal4 binding site. No enhancement was observed with UNC1999. These results demonstrate the strong influence of transcription-driven chromatin remodeling on CRISPR editing at closed chromatin.

50: Highly efficient CRISPR gene editing in yeast enabled by double selection
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Posted to bioRxiv 09 Feb 2018

Highly efficient CRISPR gene editing in yeast enabled by double selection
1,722 downloads synthetic biology

Philippe C Despres, Alexandre K Dubé, Lou Nielly-Thibault, Nozomu Yachie, Christian R Landry

CRISPR-Cas9 loss of function (LOF) and base editing screens are powerful tools in genetics and genomics. Yeast is one of the main models in genetics and genomics, yet large-scale approaches remain to be developed in this species because of low mutagenesis rates without donor DNA. We developed a double selection strategy based on co-selection that increases LOF mutation rates, both for CRISPR-Cas9 and the Target-AID base editor. We constructed the pDYSCKO vector, which is amenable to high throughput double selection for both approaches. Using modeling, we show that this improvement provides the required increased in detection power to measure the fitness effects of thousands of mutations in typical yeast pooled screens. We also show that multiplex genome editing with Cas9 causes programmable chromosomal translocations at high frequency, suggesting that multiplex editing should be performed with caution and that base-editors could be preferable tools for LOF screens.

51: Engineering Cell Sensing and Responses Using a GPCR-Coupled CRISPR-Cas System
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Posted to bioRxiv 20 Jun 2017

Engineering Cell Sensing and Responses Using a GPCR-Coupled CRISPR-Cas System
1,708 downloads synthetic biology

P. C. Dave P. Dingal, Nathan H. Kipniss, Louai Labanieh, Yuchen Gao, Lei S. Qi

G-protein coupled receptors (GPCRs) are the largest and most diverse group of membrane receptors in eukaryotes, and detects a wide array of physiological cues in the human body. We describe a new molecular device that couples CRISPR-Cas9 programmed genome regulation to natural and synthetic extracellular signals via GPCRs. The design of our synthetic device, named CRISPR ChaCha, displays superior performance over an architecture proposed by the previously reported Tango system. Using a parsimonious mathematical model and gene-reporter assays, we find that CRISPR ChaCha can recruit and activate multiple Cas9 molecules for each GPCR molecule. We also characterize key molecular features that modulate CRISPR ChaCha performance. We adopt the design to diverse GPCRs that sense synthetic and natural ligands including chemokines, mitogens, and fatty acids, and observe efficient conversion of signals to customizable genetic programs in mammalian cells, including regulation of endogenous genes. The new class of CRISPR-coupled GPCRs provides a robust and efficient platform for engineering cells with novel behaviors in response to the diverse GPCR ligand repertoire.

52: A Toolkit for Rapid Modular Construction of Biological Circuits in Mammalian Cells
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Posted to bioRxiv 26 Dec 2018

A Toolkit for Rapid Modular Construction of Biological Circuits in Mammalian Cells
1,692 downloads synthetic biology

João Pedro Fonseca, Alain R Bonny, G. Renuka Kumar, Andrew H Ng, Jason Town, Qiu Chang Wu, Elham Aslankoohi, Susan Y Chen, Patrick Harrigan, Lindsey C Osimiri, Amy L Kistler, Hana El-Samad

The ability to rapidly assemble and prototype cellular circuits is vital for biological research and its applications in biotechnology and medicine. Current methods that permit the assembly of DNA circuits in mammalian cells are laborious, slow, expensive and mostly not permissive of rapid prototyping of constructs. Here we present the Mammalian ToolKit (MTK), a Golden Gate-based cloning toolkit for fast, reproducible and versatile assembly of large DNA vectors and their implementation in mammalian models. The MTK consists of a curated library of characterized, modular parts that can be easily mixed and matched to combinatorially assemble one transcriptional unit with different characteristics, or a hierarchy of transcriptional units weaved into complex circuits. MTK renders many cell engineering operations facile, as showcased by our ability to use the toolkit to generate single-integration landing pads, to create and deliver libraries of protein variants and sgRNAs, and to iterate through Cas9-based prototype circuits. As a biological proof of concept, we used the MTK to successfully design and rapidly construct in mammalian cells a challenging multicistronic circuit encoding the Ebola virus (EBOV) replication complex. This construct provides a non-infectious biosafety level 2 (BSL2) cellular assay for exploring the transcription and replication steps of the EBOV viral life cycle in its host. Its construction also demonstrates how the MTK can enable important and time sensitive applications such as the rapid testing of pharmacological inhibitors of emerging BSL4 viruses that pose a major threat to human health.

53: Burden-driven feedback control of gene expression
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Posted to bioRxiv 20 Aug 2017

Burden-driven feedback control of gene expression
1,660 downloads synthetic biology

Francesca Ceroni, Simone Furini, Thomas E Gorochowski, A Boo, Olivier Borkowski, YN Ladak, Ali R Awan, Charlie Gilbert, Guy-Bart Stan, Tom Ellis

Cells use feedback regulation to ensure robust growth despite fluctuating demands on resources and different environmental conditions. Yet the expression of foreign proteins from engineered constructs is an unnatural burden on resources that cells are not adapted for. Here we combined multiplex RNAseq with an in vivo assay to reveal the major transcriptional changes in two E. coli strains when a set of inducible synthetic constructs are expressed. We identified that native promoters related to the heat-shock response activate expression rapidly in response to synthetic expression, regardless of the construct. Using these promoters, we built a CRISPR/dCas9-based feedback regulation system that automatically adjusts synthetic construct expression in response to burden. Cells equipped with this general-use controller maintain capacity for native gene expression to ensure robust growth and as such outperform unregulated cells at protein yields in batch production. This engineered feedback is the first example of a universal, burden-based biomolecular control system and is modular, tuneable and portable.

54: Measurements of translation initiation from all 64 codons in E. coli
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Posted to bioRxiv 14 Jul 2016

Measurements of translation initiation from all 64 codons in E. coli
1,633 downloads synthetic biology

Ariel Hecht, Jeff Glasgow, Paul R. Jaschke, Lukmaan Bawazer, Matthew S. Munson, Jennifer Cochran, Drew Endy, Marc Salit

Our understanding of translation is one cornerstone of molecular biology that underpins our capacity to engineer living matter. The canonical start codon (AUG) and a few near-cognates (GUG, UUG) are typically considered as the start codons for translation initiation in Escherichia coli (E. coli). Translation is typically not thought to initiate from the 61 remaining codons. Here, we systematically quantified translation initiation in E. coli from all 64 triplet codons. We detected protein synthesis above background initiating from at least 46 codons. Translation initiated from these non-canonical start codons at levels ranging from 0.01% to 2% relative to AUG. Translation initiation from non-canonical start codons may contribute to the synthesis of peptides in both natural and synthetic biological systems.

55: Synthesis and patterning of tunable multiscale materials with engineered cells
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Posted to bioRxiv 14 Feb 2014

Synthesis and patterning of tunable multiscale materials with engineered cells
1,626 downloads synthetic biology

Allen Y Chen, Urartu O.S. Seker, Michelle Y Lu, Robert J Citorik, Timothy Lu

A major challenge in materials science is to create self-assembling, functional, and environmentally responsive materials which can be patterned across multiple length scales. Natural biological systems, such as biofilms, shells, and skeletal tissues, implement dynamic regulatory programs to assemble complex multiscale materials comprised of living and non-living components. Such systems can provide inspiration for the design of heterogeneous functional systems which integrate biotic and abiotic materials via hierarchical self-assembly. Here, we present a synthetic-biology platform for synthesizing and patterning self-assembled functional amyloid materials across multiple length scales with bacterial biofilms. We engineered Escherichia coli curli amyloid production under the tight control of synthetic regulatory circuits and interfaced amyloids with inorganic materials to create a biofilm-based electrical switch whose conductance can be selectively toggled by specific environmental signals. Furthermore, we externally tuned synthetic biofilms to build nanoscale amyloid biomaterials with different structure and composition through the controlled expression of their constituent subunits with artificial gene circuits. By using synthetic cell-cell communication, our engineered biofilms can also autonomously manufacture dynamic materials whose structure and composition change with time. In addition, we show that by combining subunit-level protein engineering, controlled genetic expression of self-assembling subunit proteins, and macroscale spatial gradients, synthetic biofilms can pattern protein biomaterials across multiple length scales. This work lays a foundation for synthesizing, patterning, and controlling composite materials with engineered biological systems. We envision that this approach can be expanded to other cellular and biomaterials contexts for the construction of self-organizing, environmentally responsive, and tunable multiscale composite materials with heterogeneous functionalities. Now published as: Nature Materials, doi:10.1038/nmat3912

56: Communication and quorum sensing in non-living mimics of eukaryotic cells
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Posted to bioRxiv 20 Jun 2018

Communication and quorum sensing in non-living mimics of eukaryotic cells
1,617 downloads synthetic biology

Henrike Niederholtmeyer, Cynthia Chaggan, Neal K Devaraj

Cells in tissues or biofilms communicate with one another through chemical and mechanical signals to coordinate collective behaviors. Non-living cell mimics provide simplified models of natural systems, however, it has remained challenging to implement communication capabilities comparable to living cells. Here we present a porous artificial cell-mimic containing a nucleus-like DNA-hydrogel compartment that is able to express and display proteins, and communicate with neighboring cell-mimics through diffusive protein signals. We show that communication between cell-mimics allowed distribution of tasks, quorum sensing, and cellular differentiation according to local environment. Cell-mimics could be manufactured in large quantities, easily stored, chemically modified, and spatially organized into diffusively connected tissue-like arrangements, offering a means for studying communication in large ensembles of artificial cells.

57: High-Throughput Characterization of Protein-Protein Interactions by Reprogramming Yeast Mating
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Posted to bioRxiv 29 Mar 2017

High-Throughput Characterization of Protein-Protein Interactions by Reprogramming Yeast Mating
1,601 downloads synthetic biology

David Younger, Stephanie Berger, David Baker, Eric Klavins

High-throughput methods for screening protein-protein interactions enable the rapid characterization of engineered binding proteins and interaction networks. While existing approaches are powerful, none allow quantitative library-on-library characterization of protein interactions in a modifiable extracellular environment. Here, we show that sexual agglutination of S. cerevisiae can be reprogrammed to link interaction strength with mating efficiency using synthetic agglutination (SynAg). Validation of SynAg with 89 previously characterized interactions shows a log-linear relationship between mating efficiency and protein binding strength for interactions with Kd's ranging from below 500 pM to above 300 uM. Using induced chromosomal translocation to pair barcodes representing binding proteins, thousands of distinct interactions can be screened in a single pot. We demonstrate the ability to characterize protein interaction networks in a modifiable environment by introducing a soluble peptide that selectively disrupts a subset of interactions in a representative network by up to 800-fold. SynAg enables the high-throughput, quantitative characterization of protein-protein interaction networks in a fully-defined extracellular environment at a library-on-library scale.

58: Engineering Brain Parasites for Intracellular Delivery of Therapeutic Proteins
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Posted to bioRxiv 03 Dec 2018

Engineering Brain Parasites for Intracellular Delivery of Therapeutic Proteins
1,583 downloads synthetic biology

Shahar Bracha, Karoliina Hassi, Paul D. Ross, Stuart Cobb, Lilach Sheiner, Oded Rechavi

Protein therapy has the potential to alleviate many neurological diseases; however, delivery mechanisms for the central nervous system (CNS) are limited, and intracellular delivery poses additional hurdles. To address these challenges, we harnessed the protist parasite Toxoplasma gondii, which can migrate into the CNS and secrete proteins into cells. Using a fusion protein approach, we engineered T. gondii to secrete therapeutic proteins for human neurological disorders. We tested two secretion systems, generated fusion proteins that localized to the secretory organelles of T. gondii and assessed their intracellular targeting in various mammalian cells including neurons. We show that T. gondii expressing GRA16 fused to the Rett syndrome protein MeCP2 deliver a fusion protein that mimics the endogenous MeCP2, binding heterochromatic DNA in neurons. This demonstrates the potential of T. gondii as a therapeutic protein vector, which could provide either transient or chronic, in situ synthesis and delivery of intracellular proteins to the CNS.

59: Programmable bacteria induce durable tumor regression and systemic antitumor immunity
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Posted to bioRxiv 01 Mar 2019

Programmable bacteria induce durable tumor regression and systemic antitumor immunity
1,550 downloads synthetic biology

Sreyan Chowdhury, Taylor E. Hinchliffe, Samuel Castro, Courtney Coker, Nicholas Arpaia, Tal Danino

Synthetic biology is driving a new era of medicine through the genetic programming of living cells. This transformative approach allows for the creation of engineered systems that intelligently sense and respond to diverse environments, ultimately adding specificity and efficacy that extends beyond the capabilities of molecular-based therapeutics. One particular focus area has been the engineering of bacteria as therapeutic delivery systems to selectively release therapeutic payloads in vivo. Here, we engineered a non-pathogenic E. coli to specifically lyse within the tumor microenvironment and release an encoded nanobody antagonist of CD47 (CD47nb), an anti-phagocytic receptor commonly overexpressed in several human cancers. We show that intratumoral delivery of CD47nb by tumor-colonizing bacteria increases activation of tumor-infiltrating T cells, stimulates rapid tumor regression, prevents metastasis, and leads to long-term survival in a syngeneic tumor model. Moreover, we report that local injection of CD47nb bacteria stimulates systemic antitumor immune responses that reduce the growth of untreated tumors - providing, to the best of our knowledge, the first demonstration of an abscopal effect induced by a bacteria cancer therapy. Thus, engineered bacteria may be used for safe and local delivery of immunotherapeutic payloads leading to systemic antitumor immunity.

60: An Engineered Cas-Transposon System for Programmable and Precise DNA Transpositions
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Posted to bioRxiv 03 Jun 2019

An Engineered Cas-Transposon System for Programmable and Precise DNA Transpositions
1,533 downloads synthetic biology

Sway P. Chen, Harris H. Wang

Efficient targeted insertion of heterologous DNA into a genome remains a challenge in genome engineering. Recombinases that can introduce kilobase-sized DNA constructs require pre-existing recombination sites to be present in the genome and are difficult to reprogram to other loci. Genome insertion using current CRISPR-Cas methods relies on host DNA repair machinery, which is generally inefficient. Here, we describe a Cas-Transposon (CasTn) system for genomic insertions that uses a transposase fused to a catalytically-dead dCas9 nuclease to mediate programmable, site-specific transposition. CasTn combines the power of the Himar1 transposase, which inserts multi-kb DNA transposons into TA dinucleotides by a cut-and-paste mechanism, and the targeting capability of Cas9, which uses guide-RNAs to bind to specific DNA sequences. Using in vitro assays, we demonstrated that Himar-dCas9 proteins increased the frequency of transposon insertions at a single targeted TA dinucleotide by >300-fold compared to an untargeted transposase, and that site-specific transposition is dependent on target choice while robust to log-fold variations in protein and DNA concentrations. We then showed that Himar-dCas9 mediates site-specific transposition into a target plasmid in E. coli. This work provides CasTn as a new method for host-independent, programmable, targeted DNA insertions to expand the genomic engineering toolbox.

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