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1. Hydrofoam and oxygen headspace bioreactors improve cell‐free therapeutic protein production yields through enhanced oxygen transport

   https://doi.org/10.1002/btpr.3079  

   Nelson, J_Andrew_D; Barnett, R_Jordan; Hunt, J_Porter; Foutz, Isaac; Welton, Meagan; Bundy, Bradley_C (October 2020, Biotechnology Progress)

   Abstract Protein therapeutics are powerful tools in the fight against diabetes, cancers, growth disorders, and many other debilitating diseases. However, availability is limited due to cost and complications of production from living organisms. To make life‐saving protein therapeutics more available to the world, the possibility of magistral or point‐of‐care protein therapeutic production has gained focus. The recent invention and optimization of lyophilized “cell‐free” protein synthesis reagents and its demonstrated ability to produce highly active versions of FDA‐approved cancer therapeutics have increased its potential for low‐cost, single‐batch, magistral medicine. Here we present for the first time the concept of increased oxygen mass transfer in small‐batch, cell‐free protein synthesis (CFPS) reactions through air‐water foams. These “hydrofoam” reactions increased CFPS yields by up to 100%. Contrary to traditional protein synthesis using living organisms, where foam bubbles cause cell‐lysis and production losses, hydrofoam CFPS reactions are “cell‐free” and better tolerate foaming. Simulation and experimental results suggest that oxygen transfer is limiting in even small volume batch CFPS reactors and that the hydrofoam format improved oxygen transfer. This is further supported by CFPS reactions achieving higher yields when oxygen gas replaces air in the headspace of batch reactions. Improving CFPS yields with hydrofoam reduces the overall cost of biotherapeutic production, increasing availability to the developing world. Beyond protein therapeutic production, hydrofoam CFPS could also be used to enhance other CFPS applications including biosensing, biomanufacturing, and biocatalysis. 

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2. Membrane protein synthesis: no cells required

   https://doi.org/10.1016/j.tibs.2023.03.006  

   Manzer, Zachary A.; Selivanovitch, Ekaterina; Ostwalt, Alexis R.; Daniel, Susan (July 2023, Trends in Biochemical Sciences)

   Despite advances in membrane protein (MP) structural biology and a growing interest in their applications, these proteins remain challenging to study. Progress has been hindered by the complex nature of MPs and innovative methods will be required to circumvent technical hurdles. Cell-free protein synthesis (CFPS) is a burgeoning technique for synthesizing MPs directly into a membrane environment using reconstituted components of the cellular transcription and translation machinery in vitro. We provide an overview of CFPS and how this technique can be applied to the synthesis and study of MPs. We highlight numerous strategies including synthesis methods and folding environments, each with advantages and limitations, to provide a survey of how CFPS techniques can advance the study of MPs. 

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3. The all-E. coliTXTL toolbox 3.0: new capabilities of a cell-free synthetic biology platform

   https://doi.org/10.1093/synbio/ysab017  

   Garenne, David; Thompson, Seth; Brisson, Amaury; Khakimzhan, Aset; Noireaux, Vincent (August 2021, Synthetic Biology)

   null (Ed.)

   Abstract The new generation of cell-free gene expression systems enables the prototyping and engineering of biological systems in vitro over a remarkable scope of applications and physical scales. As the utilization of DNA-directed in vitro protein synthesis expands in scope, developing more powerful cell-free transcription–translation (TXTL) platforms remains a major goal to either execute larger DNA programs or improve cell-free biomanufacturing capabilities. In this work, we report the capabilities of the all-E. coli TXTL toolbox 3.0, a multipurpose cell-free expression system specifically developed for synthetic biology. In non-fed batch-mode reactions, the synthesis of the fluorescent reporter protein eGFP (enhanced green fluorescent protein) reaches 4 mg/ml. In synthetic cells, consisting of liposomes loaded with a TXTL reaction, eGFP is produced at concentrations of >8 mg/ml when the chemical building blocks feeding the reaction diffuse through membrane channels to facilitate exchanges with the outer solution. The bacteriophage T7, encoded by a genome of 40 kb and ∼60 genes, is produced at a concentration of 1013 PFU/ml (plaque forming unit/ml). This TXTL system extends the current cell-free expression capabilities by offering unique strength and properties, for testing regulatory elements and circuits, biomanufacturing biologics or building synthetic cells. 

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4. New Aequorea Fluorescent Proteins for Cell-Free Bioengineering

   https://doi.org/10.1021/acssynbio.3c00057  

   Deich, Christopher; Gaut, Nathaniel J.; Sato, Wakana; Engelhart, Aaron E.; Adamala, Katarzyna P. (April 2023, ACS Synthetic Biology)

   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. 

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5. Engineering transmembrane signal transduction in synthetic membranes using two-component systems

   https://doi.org/10.1073/pnas.2218610120  

   Peruzzi, Justin A.; Galvez, Nina R.; Kamat, Neha P. (May 2023, Proceedings of the National Academy of Sciences)

   Cells use signal transduction across their membranes to sense and respond to a wide array of chemical and physical signals. Creating synthetic systems which can harness cellular signaling modalities promises to provide a powerful platform for biosensing and therapeutic applications. As a first step toward this goal, we investigated how bacterial two-component systems (TCSs) can be leveraged to enable transmembrane-signaling with synthetic membranes. Specifically, we demonstrate that a bacterial two-component nitrate-sensing system (NarX-NarL) can be reproduced outside of a cell using synthetic membranes and cell-free protein expression systems. We find that performance and sensitivity of the TCS can be tuned by altering the biophysical properties of the membrane in which the histidine kinase (NarX) is integrated. Through protein engineering efforts, we modify the sensing domain of NarX to generate sensors capable of detecting an array of ligands. Finally, we demonstrate that these systems can sense ligands in relevant sample environments. By leveraging membrane and protein design, this work helps reveal how transmembrane sensing can be recapitulated outside of the cell, adding to the arsenal of deployable cell-free systems primed for real world biosensing. 

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