The predictable nature of DNA interactions enables the programmable assembly of highly advanced 2D and 3D DNA structures of nanoscale dimensions. The access to ever larger and more complex structures ...has been achieved through decades of work on developing structural design principles. Concurrently, an increased focus has emerged on the applications of DNA nanostructures. In its nature, DNA is chemically inert and nanostructures based on unmodified DNA mostly lack function. However, functionality can be obtained through chemical modification of DNA nanostructures and the opportunities are endless. In this review, we discuss methodology for chemical functionalization of DNA nanostructures and provide examples of how this is being used to create functional nanodevices and make DNA nanostructures more applicable. We aim to encourage researchers to adopt chemical modifications as part of their work in DNA nanotechnology and inspire chemists to address current challenges and opportunities within the field.
Abstract
Labelling of oligonucleotides with dyes, targeting ligands, and other moieties has become ever more essential in life-sciences. Conventionally, modifications are introduced to ...oligonucleotides during solid phase synthesis by special phosphoramidites functionalised with a chemical handle or the desired functional group. In this work, we present a facile and inexpensive method to introduce modifications to oligonucleotides without the need for special phosphoramidites. Sulfonyl azides are applied to react with one or more selected phosphite intermediates during solid phase synthesis. We have prepared 11 sulfonyl azides with different chemical handles such as amine, azide, alkyne, and thiol, and we have further introduced functionalities such as pyrene, other dyes, photo-switchable azobenzenes, and a steroid. The method is compatible with current phosphoramidite-based automated oligonucleotide synthesis and serves as a simple alternative to the unstable and expensive special phosphoramidites currently used for conjugation to oligonucleotides.
Abstract
Conjugates of therapeutic oligonucleotides (ONs) including peptide conjugates, provide a potential solution to the major challenge of specific tissue delivery faced by this class of drugs. ...Conjugations are often positioned terminal at the ONs, although internal placement of other chemical modifications are known to be of critical importance. The introduction of internal conjugation handles in chemically modified ONs require highly specialized and expensive nucleoside phosphoramidites. Here, we present a method for synthesizing a library of peptide–siRNA conjugates by conjugation at internal phosphorous positions via sulfonylphosphoramidate modifications incorporated into the sense strand. The sulfonylphosphoramidate modification offers benefits as it can be directly incorporated into chemically modified ONs by simply changing the oxidation step during synthesis, and furthermore holds the potential to create multifunctionalized therapeutic ONs. We have developed a workflow using a novel pH-controlled amine-to-amine linker that yields peptide–siRNA conjugates linked via amide bonds, and we have synthesized conjugates between GLP1 peptides and a HPRT1 siRNA as a model system. The in vitro activity of the conjugates was tested by GLP1R activity and knockdown of the HPRT1 gene. We found that conjugation near the 3′-end is more favorable than certain central internal positions and different internal conjugation strategies were compared.
Graphical Abstract
Graphical Abstract
Conjugation of DNA to proteins is increasingly used in academia and industry to provide proteins with tags for identification or handles for hybridization to other DNA strands. Assay technologies ...such as immuno-PCR and proximity ligation and the imaging technology DNA-PAINT require DNA–protein conjugates. In DNA nanotechnology, the DNA handle is exploited to precisely position proteins by self-assembly. For these applications, site-selective conjugation is almost always desired because fully functional proteins are required to maintain the specificity of antibodies and the activity of enzymes. The introduction of a bioorthogonal handle at a specific position of a protein by recombinant techniques provides an excellent approach to site-specific conjugation, but for many laboratories and for applications where several proteins are to be labeled, the expression of recombinant proteins may be cumbersome. In recent years, a number of chemical methods that target conjugation to specific sites at native proteins have become available, and an overview of these methods is provided in this Account. Our laboratory has investigated DNA-templated protein conjugation (DTPC), which offers an alternative approach to site-selective conjugation of DNA to proteins. The method is inspired by the concept of DNA-templated synthesis where functional groups conjugated to DNA strands are preorganized by DNA hybridization to dramatically increase the reaction rate. In DPTC, we target metal binding sites in proteins to template selective covalent conjugation reactions. By chelation of a DNA–metal complex with a metal binding site of the protein, an electrophile on a second DNA strand is aligned for reaction with a lysine side chain on the protein in the proximity of the metal binding site. The method is quite general because approximately one-third of all wild-type proteins contain metal-binding sites, including many IgG antibodies, and it is also applicable to His-tagged proteins. This emerging field provides direct access to site-selective conjugates of DNA to commercially available proteins. In this Account, we introduce these methods to the reader and describe current developments and future aspects.
DNA nanotechnology has the power to form self-assembled and well-defined nanostructures, such as DNA origami, where the relative positions of each atom are known with subnanometer precision. Our ...ability to synthesize oligonucleotides with chemical modifications in almost any desired position provides rich opportunity to incorporate molecules, biomolecules, and a variety of nanomaterials in specific positions on DNA nanostructures. Several standard modifications for oligonucleotides are available commercially, such as dyes, biotin, and chemical handles, and such modified oligonucleotides can be applied directly for integration in DNA nanostructures. In another approach, various molecules and nanomaterials have been functionalized with DNA for incorporation in DNA nanostructures by hybridization to staple strands extending from the origami structure. Multiple copies of functionalities such as hydrocarbons or steroids have been introduced to change the surface properties of DNA origami structures, either to protect the DNA nanostructure or to dock it into membranes and other hydrophobic surfaces. DNA nanostructures have also been used to control covalent chemical reactions. This article provides an introduction to chemical methods applied to DNA nanotechnology and, through examples, shows how this increases the potential of DNA nanostructures as functional nanomaterials.
The inherent specificity of DNA sequence hybridization has been extensively exploited to develop bioengineering applications. Nevertheless, the structural potential of DNA has been far less explored ...for creating non-canonical DNA-based reactions. Here we develop a DNA origami-enabled highly localized metallization reaction for intrinsic metallization patterning with 10-nm resolution. Both theoretical and experimental studies reveal that low-valence metal ions (Cu
and Ag
) strongly coordinate with DNA bases in protruding clustered DNA (pcDNA) prescribed on two-dimensional DNA origami, which results in effective attraction within flexible pcDNA strands for site-specific pcDNA condensation. We find that the metallization reactions occur selectively on prescribed sites while not on origami substrates. This strategy is generically applicable for free-style metal painting of alphabet letters, digits and geometric shapes on all-DNA substrates with near-unity efficiency. We have further fabricated single- and double-layer nanoscale printed circuit board (nano-PCB) mimics, shedding light on bio-inspired fabrication for nanoelectronic and nanophotonic applications.
The spatially controlled positioning of functional materials by self-assembly is one of the fundamental visions of nanotechnology. Major steps towards this goal have been achieved using DNA as a ...programmable building block. This tutorial review will focus on one of the most promising methods: DNA origami. The basic design principles, organization of a variety of functional materials and recent implementation of DNA robotics are discussed together with future challenges and opportunities.
Fluorescent RNA aptamers are useful as markers for tracking RNA molecules inside cells and for creating biosensor devices. Förster resonance energy transfer (FRET) based on fluorescent proteins has ...been used to detect conformational changes, however, such FRET devices have not yet been produced using fluorescent RNA aptamers. Here we develop an RNA aptamer-based FRET (apta-FRET) system using single-stranded RNA origami scaffolds. To obtain FRET, the fluorescent aptamers Spinach and Mango are placed in close proximity on the RNA scaffolds and a new fluorophore is synthesized to increase spectral overlap. RNA devices that respond to conformational changes are developed, and finally, apta-FRET constructs are expressed in E. coli where FRET is observed, demonstrating that the apta-FRET system is genetically encodable and that the RNA nanostructures fold correctly in bacteria. We anticipate that the RNA apta-FRET system could have applications as ratiometric sensors for real-time studies in cell and synthetic biology.
The inherent redox activity of dopamine enables its direct electrochemical in vivo analysis ( Venton B. J. ; Wightman M. R. Anal. Chem. 2003, 75, 414A ). However, dopamine analysis is complicated by ...the interference from other electrochemically active endogenous compounds present in the brain, including dopamine precursors and metabolites and other neurotransmitters (NT). Here we report an electrochemical RNA aptamer-based biosensor for analysis of dopamine in the presence of other NT. The biosensor exploits a specific binding of dopamine by the RNA aptamer, immobilized at a cysteamine-modified Au electrode, and further electrochemical oxidation of dopamine. Specific recognition of dopamine by the aptamer allowed a selective amperometric detection of dopamine within the physiologically relevant 100 nM to 5 μM range in the presence of competitive concentrations of catechol, epinephrine, norepinephrine, 3,4-dihydroxy-phenylalanine (l-DOPA), 3,4-dihydroxyphenylacetic acid (DOPAC), methyldopamine, and tyramine, which gave negligible signals under conditions of experiments (electroanalysis at 0.185 V vs Ag/AgCl). The interference from ascorbic and uric acids was eliminated by application of a Nafion-coated membrane. The aptasensor response time was <1 s, and the sensitivity of analysis was 62 nA μM–1 cm–2. The proposed design of the aptasensor, based on electrostatic interactions between the positively charged cysteamine-modified electrode and the negatively charged aptamer, may be used as a general strategy not to restrict the conformational freedom and binding properties of surface-bound aptamers and, thus, be applicable for the development of other aptasensors.
An electrochemical RNA aptamer-based biosensor for rapid and label-free detection of the bronchodilator theophylline was developed. The 5‘-disulfide-functionalized end of the RNA aptamer sequence was ...immobilized on a gold electrode, and the 3‘-amino-functionalized end was conjugated with a ferrocene (Fc) redox probe. Upon binding of theophylline the aptamer switches conformation from an open unfolded state to a closed hairpin-type conformation, resulting in the increased electron-transfer efficiency between Fc and the electrode. The electrochemical response, which was measured by differential pulse voltammetry, reaches saturation within a few minutes after addition of theophylline, and the dynamic range for detecting theophylline is 0.2−10 μM. The electrode displays an inhibited response when applied directly in serum samples treated with RNase inhibitors; however a full response to the theophylline serum concentration was obtained by transferring the electrode to blank serum-free buffer solutions. It was demonstrated that theophylline is detected with high selectivity in the presence of caffeine and theobromine.
PDF
