pH‐Gated Activation of Gene Transcription and Translation in Biocatalytic Metal–Organic Framework Artificial Cells

Cell-Free Gene Expression: Methods and Applications

Cell-free gene expression (CFE) systems empower synthetic biologists to build biological molecules and processes outside of living intact cells. The foundational principle is that precise, complex biomolecular transformations can be conducted in purified enzyme or crude cell lysate systems. This concept circumvents mechanisms that have evolved to facilitate species survival, bypasses limitations on molecular transport across the cell wall, and provides a significant departure from traditional, cell-based processes that rely on microscopic cellular "reactors." In addition, cell-free systems are inherently distributable through freeze-drying, which allows simple distribution before rehydration at the point-of-use. Furthermore, as cell-free systems are nonliving, they provide built-in safeguards for biocontainment without the constraints attendant on genetically modified organisms. These features have led to a significant increase in the development and use of CFE systems over the past two decades. Here, we discuss recent advances in CFE systems and highlight how they are transforming efforts to build cells, control genetic networks, and manufacture biobased products.

Electrochemical and Biocatalytic Signal-Controlled Payload Release from a Metal-Organic Framework

A metal-organic framework (MOF), ZIF-8, which is stable at neutral and slightly basic pH values in aqueous solutions and destabilized/dissolved under acidic conditions, is loaded with a pH-insensitive fluorescent dye, rhodamine-B isothiocyanate, as a model payload species. Then, the MOF species are immobilized at an electrode surface. The local (interfacial) pH value is rapidly decreased by means of an electrochemically stimulated ascorbate oxidation at +0.4 V (Ag/AgCl/KCl). Oxygen reduction upon switching the applied potential to -0.8 V allows to return the local pH to the neutral/basic pH, then stopping rapidly the release process. The developed method allows electrochemical control over stimulated or inhibited payload release processes from the MOF. The pH variation proceeds in a thin film of the solution near the electrode surface. The switchable release process is realized in a buffer solution and undiluted human serum. As the second option, the pH decrease stimulating the release process is achieved upon an enzymatic reaction using esterase and ester substrate. This approach potentially allows the release activation controlled by numerous enzymes assembled in complex biocatalytic cascades. It is expected that related electrochemical or biocatalytic systems can represent novel signal-responding materials with switchable features for delivering (bio)molecules within biomedical applications.

Nanobiohybrids: Synthesis strategies and environmental applications from micropollutants sensing and removal to global warming mitigation

Micropollutants contamination and global warming are critical environmental issues that require urgent attention due to natural and anthropogenic activities posing serious threats to human health and ecosystems. However, traditional technologies (such as adsorption, precipitation, biodegradation, and membrane separation et al.) are facing challenges of low utilization efficiency of oxidants, poor selectivity, and complex in-situ monitoring operations. To address these technical bottlenecks, nanobiohybrids, synthesized by interfacing the nanomaterials and biosystems, have recently emerged as eco-friendly technologies. In this review, we summarize the synthesis approaches of nanobiohybrids and their utilization as emerging environmental technologies for addressing environmental problems. Studies demonstrate that enzymes, cells, and living plants can be integrated with a wide range of nanomaterials including reticular frameworks, semiconductor nanoparticles and single-walled carbon nanotubes. Moreover, nanobiohybrids demonstrate excellent performance for micropollutant removal, carbon dioxide conversion, and sensing of toxic metal ions and organic micropollutants. Therefore, nanobiohybrids are expected to be environmental friendly, efficient, and cost-effective techniques for addressing environmental micropollutants issues and mitigating global warming, benefiting both humans and ecosystems alike.

Compartmentalized Cell-Free Expression Systems for Building Synthetic Cells

One of the grand challenges in bottom-up synthetic biology is the design and construction of synthetic cellular systems. One strategy toward this goal is the systematic reconstitution of biological processes using purified or non-living molecular components to recreate specific cellular functions such as metabolism, intercellular communication, signal transduction, and growth and division. Cell-free expression systems (CFES) are in vitro reconstitutions of the transcription and translation machinery found in cells and are a key technology for bottom-up synthetic biology. The open and simplified reaction environment of CFES has helped researchers discover fundamental concepts in the molecular biology of the cell. In recent decades, there has been a drive to encapsulate CFES reactions into cell-like compartments with the aim of building synthetic cells and multicellular systems. In this chapter, we discuss recent progress in compartmentalizing CFES to build simple and minimal models of biological processes that can help provide a better understanding of the process of self-assembly in molecularly complex systems.

Tailoring head-tail mesoporous silica nanoparticles for enhanced gene transfection

Plasmid DNA (pDNA) delivery has attracted extensive research interest due to its great potential in gene therapy. The design of efficient nano-vectors to promote cellular delivery and transfection of gene molecules is the key to success. Compared to conventional nanocarriers with spherical geometry, asymmetric nanoparticles have been well documented showing enhanced cellular uptake and drug delivery capability. However, the impact of asymmetric nanostructures on pDNA binding and following intracellular delivery performance has been less reported. Herein, asymmetric head-tail mesoporous silica nanoparticles (HTMSNs) with tailored tail lengths were synthesized and employed as nano-vectors for pDNA delivery. The nanostructures of HTMSNs were carefully characterized by electron tomography. The pDNA binding, cellular uptake and gene transfection capabilities of engineered asymmetric nanoparticles were compared with symmetric dendritic mesoporous silica nanoparticles (DMSNs). The results showed that the asymmetric morphology of nanoparticles promoted pDNA binding and cell internalization, where HTMSNs-66 with a specific tail length of 66 nm achieved the highest transfection efficiency. This study reveals the impact of asymmetric nanostructure on DNA interaction, and provides guidance in future designs of non-viral nano-vectors for efficient gene delivery.

Metal-Organic Frameworks as a Versatile Materials Platform for Unlocking New Potentials in Biocatalysis

Biocatalysts immobilization with nanomaterials has promoted the development of biocatalysis significantly and made it an indispensable part of catalysis industries nowadays. Metal-organic frameworks (MOFs), constructed from organic linkers and metal ions or clusters, have raised significant interests for biocatalysts immobilization in recent years. The diversity of building units, molecular-scale tunability, and modular synthetic routes of MOFs greatly expand its ability as the host to integrate with biocatalysts. In this review, the general synthetic strategies of MOFs with biocatalysts are first summarized. Then, the recent progress of MOFs as a versatile host for a series of biocatalysts, including natural enzymes, nanozymes, and organism-based biocatalysts, followed by the introduction of MOFs themselves as biocatalysts, is discussed. Furthermore, the stimuli-responsive properties of MOFs themselves or the additional functionalization of protein, polymer, and peptide within/on MOF that enable the biocatalysts with the controllable and tunable behavior are also summarized, which could unlock new potentials in biocatalysis. Finally, a perspective of the upcoming challenges, potential impacts, and future directions of biocatalytic MOFs is provided.

Interwoven MOF-Coated Janus Cells as a Novel Carrier of Toxic Proteins

Two major issues in cell-mediated drug delivery systems (c-DDS) are the availability of free cell surfaces for the binding of the cells to the target or to their microenvironment and internalization of the cytotoxic drug. In this study, the Janus structure, MOF nanoparticles, and tannic acid (TA) are utilized to address these issues. Janus carrier cells coated with metal-organic frameworks (MOFs) are produced by asymmetrically immobilizing the nanoparticles of a MOF based on zinc with cytotoxic enzymes that are internally encapsulated on the surface of carrier cells. By maintaining the biological and structural features of regular living cells, the MOF-coated Janus cells developed in the present study preserve the intrinsic binding capacity of the cells to their microenvironment. Interconnected MOFs loaded onto the other face of the Janus cells cannot penetrate the cell. Therefore, the carrier cells are protected from the cytotoxic drug contained in MOFs. These MOF-Janus carrier cells are demonstrated to successfully eliminate three-dimensional (3D) tumor spheroids when a chemotherapeutic protein of proteinase K is released from the MOF nanoparticles in an acid environment. The ease with which the MOF-Janus carrier cells are prepared (in 15 min), and the ability to carry a variety of enzymes and even multiple ones should make the developed system attractive as a general platform for drug delivery in various applications, including combination therapy.