Cell-surface receptor control that depends on the size of a synthetic equilateral-triangular RNA-protein complex

Structural insights into lab-coevolved RNA-RBP pairs and applications of synthetic riboswitches in cell-free system

CS1-LS4 and CS2-LS12 are ultra-high affinity and orthogonal RNA-protein pairs that were identified by PD-SELEX (Phage Display coupled with Systematic Evolution of Ligands by EXponential enrichment). To investigate the molecular basis of the lab-coevolved RNA-RBP pairs, we determined the structures of the CS1-LS4 and CS2-LS12 complexes and the LS12 homodimer in an RNA-free state by X-ray crystallography. The structural analyses revealed that the lab-coevolved RNA-RBPs have acquired unique molecular recognition mechanisms, whereas the overall structures of the RNP complexes were similar to the typical kink-turn RNA-L7Ae complex. The orthogonal RNA-RBP pairs were applied to construct high-performance cell-free riboswitches that regulate translation in response to LS4 or LS12. In addition, by using the orthogonal protein-responsive switches, we generated an AND logic gate that outputs staphylococcal γ-hemolysin in cell-free system and carried out hemolysis assay and calcein leakage assay using rabbit red blood cells and artificial cells, respectively.

An RNA Triangle with Six Ribozyme Units Can Promote a Trans-Splicing Reaction through Trimerization of Unit Ribozyme Dimers

Ribozymes are catalytic RNAs that are attractive platforms for the construction of nanoscale objects with biological functions. We designed a dimeric form of the Tetrahymena group I ribozyme as a unit structure in which two ribozymes were connected in a tail-to-tail manner with a linker element. We introduced a kink-turn motif as a bent linker element of the ribozyme dimer to design a closed trimer with a triangular shape. The oligomeric states of the resulting ribozyme dimers (kUrds) were analyzed biochemically and observed directly by atomic force microscopy (AFM). Formation of kUrd oligomers also triggered trans-splicing reactions, which could be monitored with a reporter system to yield a fluorescent RNA aptamer as the trans-splicing product.

RNA nanostructures and scaffolds for biotechnology applications

RNA plays important roles in the regulation of gene expressions and other cellular functions. It functions as both as an informational carrier and a nanomachine due to its complementary base-pairing ability and complexed three-dimensional structure. Several nanostructures have been designed and constructed by exploiting these natural RNA properties. In this review, we will introduce the design principles of RNA nanostructures and their biotechnology applications as molecular scaffolds. RNA-based molecular scaffolds can control the accumulation and interaction of target proteins at nanometer-scale to regulate the function of bacterial and mammalian cells. Combining useful property of RNA as a nano-material and a molecular scaffold may provide us powerful tools in biological research, bioengineering, and future medicine.

Incorporation of native antibodies and Fc-fusion proteins on DNA nanostructures via a modular conjugation strategy

A photocrosslinkable protein G adapter was used to site-specifically conjugate complex native proteins to oligonucleotides, allowing for efficient incorporation on DNA origami nanostructures.

A photocrosslinkable protein G variant was used as an adapter protein to covalently and site-specifically conjugate an antibody and an Fc-fusion protein to an oligonucleotide. This modular approach enables straightforward decoration of DNA nanostructures with complex native proteins while retaining their innate binding affinity, allowing precise control over the nanoscale spatial organization of such proteins for in vitro and in vivo biomedical applications.

RNA Nanotherapeutics for the Amelioration of Astroglial Reactivity

In response to injuries to the CNS, astrocytes enter a reactive state known as astrogliosis, which is believed to be deleterious in some contexts. Activated astrocytes overexpress intermediate filaments including glial fibrillary acidic protein (GFAP) and vimentin (Vim), resulting in entangled cells that inhibit neurite growth and functional recovery. Reactive astrocytes also secrete inflammatory molecules such as Lipocalin 2 (Lcn2), which perpetuate reactivity and adversely affect other cells of the CNS. Herein, we report proof-of-concept use of the packaging RNA (pRNA)-derived three-way junction (3WJ) motif as a platform for the delivery of siRNAs to downregulate such reactivity-associated genes. In vitro, siRNA-3WJs induced a significant knockdown of Gfap, Vim, and Lcn2 in a model of astroglial activation, with a concomitant reduction in protein expression. Knockdown of Lcn2 also led to reduced protein secretion from reactive astroglial cells, significantly impeding the perpetuation of inflammation in otherwise quiescent astrocytes. Intralesional injection of anti-Lcn2-3WJs in mice with contusion spinal cord injury led to knockdown of Lcn2 at mRNA and protein levels in vivo. Our results provide evidence for siRNA-3WJs as a promising platform for ameliorating astroglial reactivity, with significant potential for further functionalization and adaptation for therapeutic applications in the CNS.

Protein-driven RNA nanostructured devices that function in vitro and control mammalian cell fate

Nucleic acid nanotechnology has great potential for future therapeutic applications. However, the construction of nanostructured devices that control cell fate by detecting and amplifying protein signals has remained a challenge. Here we design and build protein-driven RNA-nanostructured devices that actuate in vitro by RNA-binding-protein-inducible conformational change and regulate mammalian cell fate by RNA–protein interaction-mediated protein assembly. The conformation and function of the RNA nanostructures are dynamically controlled by RNA-binding protein signals. The protein-responsive RNA nanodevices are constructed inside cells using RNA-only delivery, which may provide a safe tool for building functional RNA–protein nanostructures. Moreover, the designed RNA scaffolds that control the assembly and oligomerization of apoptosis-regulatory proteins on a nanometre scale selectively kill target cells via specific RNA–protein interactions. These findings suggest that synthetic RNA nanodevices could function as molecular robots that detect signals and localize target proteins, induce RNA conformational changes, and programme mammalian cellular behaviour.

Nucleic acid nanotechnology has great potential for future therapeutic applications. Here the authors build protein-driven RNA nanostructures that can function within mammalian cells and regulate the cell fate.

Supramolecular Protein Assemblies Based on DNA Templates

DNA plays an important role in the process of protein assembly. DNA viruses such as the M13 virus are typical examples in which single DNA genomes behave as templates to induce the assembly of multiple major coat protein (PVIII) monomers. Thus, the design of protein assemblies based on DNA templates attracts much interest in the construction of supramolecular structures and materials. With the development of DNA nanotechnology, precise 1D and 3D protein nanostructures have been designed and constructed by using DNA templates through DNA-protein interactions, protein-ligand interactions, and protein-adapter interactions. These DNA-templated protein assemblies show great potential in catalysis, medicine, light-responsive systems, drug delivery, and signal transduction. Herein, we review the progress on DNA-based protein nanostructures that possess sophisticated nanometer-sized structures with programmable shapes and stimuli-responsive parameters, and we present their great potential in the design of biomaterials and biodevices in the future.

Designing synthetic RNA for delivery by nanoparticles

The rapid development of synthetic biology and nanobiotechnology has led to the construction of various synthetic RNA nanoparticles of different functionalities and potential applications. As they occur naturally, nucleic acids are an attractive construction material for biocompatible nanoscaffold and nanomachine design. In this review, we provide an overview of the types of RNA and nucleic acid's nanoparticle design, with the focus on relevant nanostructures utilized for gene-expression regulation in cellular models. Structural analysis and modeling is addressed along with the tools available for RNA structural prediction. The functionalization of RNA-based nanoparticles leading to prospective applications of such constructs in potential therapies is shown. The route from the nanoparticle design and modeling through synthesis and functionalization to cellular application is also described. For a better understanding of the fate of targeted RNA after delivery, an overview of RNA processing inside the cell is also provided.

RNA and RNP as Building Blocks for Nanotechnology and Synthetic Biology

Recent technologies that aimed to elucidate cellular function have revealed essential roles for RNA molecules in living systems. Our knowledge concerning functional and structural information of naturally occurring RNA and RNA-protein (RNP) complexes is increasing rapidly. RNA and RNP interaction motifs are structural units that function as building blocks to constitute variety of complex structures. RNA-central synthetic biology and nanotechnology are constructive approaches that employ the accumulated information and build synthetic RNA (RNP)-based circuits and nanostructures. Here, we describe how to design and construct synthetic RNA (RNP)-based devices and structures at the nanometer-scale for biological and future therapeutic applications. RNA/RNP nanostructures can also be utilized as the molecular scaffold to control the localization or interactions of target molecule(s). Moreover, RNA motifs recognized by RNA-binding proteins can be applied to make protein-responsive translational "switches" that can turn gene expression "on" or "off" depending on the intracellular environment. This "synthetic RNA and RNP world" will expand tools for nanotechnology and synthetic biology. In addition, these reconstructive approaches would lead to a greater understanding of building principle in naturally occurring RNA/RNP molecules and systems.

Artificial Formation and Tuning of Glycoprotein Networks on Live Cell Membranes: A Single-Molecule Tracking Study

We present a method to artificially induce network formation of membrane glycoproteins and show the precise tuning of their interconnection on living cells. For this, membrane glycans are first metabolically labeled with azido sugars and then tagged with biotin by copper-free click chemistry. Finally, these biotin-tagged membrane proteins are interconnected with streptavidin (SA) to form an artificial protein network in analogy to a lectin-induced lattice. The degree of network formation can be controlled by the concentration of SA, its valency, and the concentration of biotin on membrane proteins. This was verified by investigation of the spatiotemporal dynamics of the SA-protein networks employing single-molecule tracking. It was also proven that this network formation strongly influences the biologically relevant process of endocytosis as it is known from natural lattices on the cell surface.

Designed Regular Tetragon-Shaped RNA-Protein Complexes with Ribosomal Protein L1 for Bionanotechnology and Synthetic Biology

RNA nanotechnology has been established by employing the molecular architecture of RNA structural motifs. Here, we report two designed RNA-protein complexes (RNPs) composed of ribosomal protein L1 (RPL1) and its RNA-binding motif that are square-shaped nano-objects. The formation and the shape of the objects were confirmed by gel electrophoresis analysis and atomic force microscopy, respectively. Any protein can be attached to the RNA via a fusion protein with RPL1, indicating that it can be used as a scaffold for loading a variety of functional proteins or for building higher-order structures. In summary, the RNP object will serve as a useful tool in the fields of bionanotechnology and synthetic biology. Moreover, the RNP interaction enhances the RNA stability against nucleases, rendering these complexes stable in cells.

A purification method for a molecular complex in which a scaffold molecule is fully loaded with heterogeneous molecules

An affinity resin-based pull-down method is convenient for the purification of biochemical materials. However, its use is difficult for the isolation of a molecular complex fully loaded with multiple components from a reaction mixture containing the starting materials and intermediate products. To overcome this problem, we have developed a new purification procedure that depends on sequential elimination of the residues. In practice, two affinity resins were used for purifying a triangular-shaped RNP (RNA-protein complex) consisting of three ribosomal proteins (L7Ae) bound to an RNA scaffold. First, a resin with immobilized L7Ae protein captured the incomplete RNP complexes and the free RNA scaffold. Next, another resin with an immobilized chemically modified RNA of a derivative of Box C/D motif, the binding partner of L7Ae, was used to capture free protein. The complete triangular RNP was successfully purified from the mixture by these two steps. Obviously, the purified triangular RNP displaying three protein-binding peptides exhibited an improved performance when compared with the unrefined product. Conceptually, this purification procedure should be applicable for the purification of a variety of complexes consisting of multiple components other than RNP.