A Light-powered single-stranded DNA molecular motor with colour-selective single-step control.

To-down control of small motion is possible through top-down controlled molecular motors in replacement of larger actuators like MEMS or NEMS (micro- or nano-electromechanical systems) in the current precision technology. Improving top-down control of molecular motors to every single step is desirable for this purpose, and also for synchronization of motor actions for amplified effects. Here we report a designed single-stranded DNA molecular motor powered by alternated ultraviolet and visible light for processive track-walking, with the two light colours each locking the motor in a full directional step to allow saturated driving but no overstepping. This novel nano-optomechanical driving mechanism pushes the top-down control of molecular motors down to every single step, thus providing a key technical capability to advance the molecular motor-based precision technology and also motor synchronization for amplified effects.

DNA Reaction System That Acquires Classical Conditioning.

Biochemical reaction networks can exhibit plastic adaptation to alter their functions in response to environmental changes. This capability is derived from the structure and dynamics of the reaction networks and the functionality of the biomolecule. This plastic adaptation in biochemical reaction systems is essentially related to memory and learning capabilities, which have been studied in DNA computing applications for the past decade. However, designing DNA reaction systems with memory and learning capabilities using the dynamic properties of biochemical reactions remains challenging. In this study, we propose a basic DNA reaction system design that acquires classical conditioning, a phenomenon underlying memory and learning, as a typical learning task. Our design is based on a simple mechanism of five DNA strand displacement reactions and two degradative reactions. The proposed DNA circuit can acquire or lose a new function under specific conditions, depending on the input history formed by repetitive stimuli, by exploiting the dynamic properties of biochemical reactions induced by different input timings.

Rapid Chemical Ligation of DNA and Acyclic Threoninol Nucleic Acid (aTNA) for Effective Nonenzymatic Primer Extension.

Previously, nonenzymatic primer extension reaction of acyclic l-threoninol nucleic acid (L-aTNA) was achieved in the presence of N-cyanoimidazole (CNIm) and Mn2+; however, the reaction conditions were not optimized and a mechanistic insight was not sufficient. Herein, we report investigation of the kinetics and reaction mechanism of the chemical ligation of L-aTNA to L-aTNA and of DNA to DNA. We found that Cd2+, Ni2+, and Co2+ accelerated ligation of both L-aTNA and DNA and that the rate-determining step was activation of the phosphate group. The activation was enhanced by duplex formation between a phosphorylated L-aTNA fragment and template, resulting in unexpectedly more effective L-aTNA ligation than DNA ligation. Under optimized conditions, an 8-mer L-aTNA primer could be elongated by ligation to L-aTNA trimers to produce a 29-mer full-length oligomer with 60% yield within 2 h at 4 °C. This highly effective chemical ligation system will allow construction of artificial genomes, robust DNA nanostructures, and xeno nucleic acids for use in selection methods. Our findings also shed light on the possible pre-RNA world.

Methyl group configuration on acyclic threoninol nucleic acids (aTNAs) impacts supramolecular properties.

We have synthesized acyclic allo-threoninol nucleic acids (allo-aTNAs), artificial xeno-nucleic acids (XNAs) that are diastereomers of acyclic threoninol nucleic acids (aTNAs), and have investigated their supramolecular properties. The allo-aTNAs formed homo-duplexes in an antiparallel manner but with lower thermal stability than DNA, whereas aTNAs formed extremely stable homo-duplexes. The allo-aTNAs formed duplexes with complementary aTNAs and serinol nucleic acid (SNA). The affinities of L-allo-aTNA were the highest for L-aTNA and the lowest for D-aTNA, with SNA being intermediate. The affinities of D-allo-aTNA were the reverse. Circular dichroism measurements revealed that L- and D-allo-aTNAs had weak right-handed and left-handed helicities, respectively. The weak helicity of allo-aTNAs likely explains the poor chiral discrimination of these XNAs, which is in contrast to aTNAs that have strong helical orthogonality. Energy-minimized structures of L-allo-aTNA/RNA and L-allo-aTNA/L-allo-aTNA indicated that the methyl group on the allo-aTNA strand is unfavourable for duplex formation. In contrast, the methyl group on L-aTNA likely stabilizes the duplex structure via hydrophobic effects and van der Waals interactions. Thus, the configuration of the methyl group on the XNA scaffold had an unexpectedly large impact on the hybridization ability and structure.

Orthogonal Amplification Circuits Composed of Acyclic Nucleic Acids Enable RNA Detection.

Construction of complex DNA circuits is difficult due to unintended hybridization and degradation by enzymes under biological conditions. We herein report a hybridization chain reaction (HCR) circuit composed of left-handed acyclic d-threoninol nucleic acid (d-aTNA), which is orthogonal to right-handed DNA and RNA. Because of its high thermal stability, use of an aTNA hairpin with a short 7 base-pair stem ensured clear ON-OFF control of the HCR circuit. The aTNA circuit was stable against nucleases. A circuit based on right-handed acyclic l-threoninol nucleic acid (l-aTNA) was also designed, and high orthogonality between d- and l-aTNA HCRs was confirmed by activation of each aTNA HCR via a corresponding input strand. A dual OR logic gate was successfully established using serinol nucleic acid (SNA), which could initiate both d- and l-aTNA circuits. The d-aTNA HCR was used for an RNA-dependent signal amplification system via the SNA interface. The design resulted in 80% yield of the cascade reaction in 3000 s without a significant leak. This work represents the first example of use of heterochiral HCR circuits for detection of RNA molecules. The method has potential for direct visualization of RNA in vivo and the FISH method.

Renewable DNA Proportional-Integral Controller with Photoresponsive Molecules.

A molecular robot is an intelligent molecular system. A typical control problem of molecular robots is to maintain the concentration of a specific DNA strand at the desired level, which is typically attained by a molecular feedback control mechanism. A molecular feedback system can be constructed in a bottom-up method by transforming a nonlinear chemical reaction system into a pseudo-linear system. This method enables the implementation of a molecular proportional-integral (PI) controller on a DNA reaction system. However, a DNA reaction system is driven by fuel DNA strand consumption, and without a sufficient amount of fuel strands, the molecular PI controller cannot perform normal operations as a concentration regulator. In this study, we developed a design method for a molecular PI control system to regenerate fuel strands by introducing photoresponsive reaction control. To this end, we employed a photoresponsive molecule, azobenzene, to guide the reaction direction forward or backward using light irradiation. We validated our renewable design of the PI controller by numerical simulations based on the reaction kinetics. We also confirmed the proof-of-principle of our renewable design by conducting experiments using a basic DNA circuit.

Xeno nucleic acids (XNAs) having non-ribose scaffolds with unique supramolecular properties.

DNA and RNA have significance as genetic materials, therapeutic potential, and supramolecular properties. Advances in nucleic acid chemistry have enabled large-scale synthesis of DNA and RNA oligonucleotides and oligomers of non-natural nucleic acids, including artificial nucleic acids (xeno nucleic acids; XNAs) with non-ribose scaffolds. In this feature article, we review the chemical structures of XNAs with non-ribose scaffolds, their hybridization abilities, and their unique behaviors with a particular focus on the acyclic XNAs. First, we overview XNAs with non-ribose cyclic scaffolds and then those with acyclic scaffolds by focusing on their hybridization abilities with themselves and with DNA and RNA, and discuss the unexpectedly stable homo-duplex formation of acyclic XNAs. Next, we shed light on our acyclic threoninol nucleic acid (aTNA) and serinol nucleic acid (SNA) and show their helical preferences based on their chirality, then orthogonal control of hybridization and helical amplification of achiral XNAs are demonstrated. Finally, we show non-enzymatic template-directed synthesis of L-aTNA, and the creation of an artificial genetic system with XNAs with non-ribose scaffolds is described as a future prospect.

A Pyrene-Modified Serinol Nucleic Acid Nanostructure Converts the Chirality of Threoninol Nucleic Acids into Circularly Polarized Luminescence Signals.

Herein is reported a circularly polarized luminescent (CPL) probe that can respond to the chirality of nucleic acids. An achiral nanostructure was prepared by the hybridization of symmetric serinol nucleic acid (SNA) containing pyrene-modified residues. When chiral oligomers that were complementary to the SNA were added, they induced helicity into the SNA nanowire. Efficient circular dichroism (CD) signal amplification was observed when pyrene was attached to uracil bases through a rigid alkynyl linker. Both CPL and CD signals were observed; they depended on the chirality of the added acyclic threoninol nucleic acid (aTNA) oligomer. This system can be used to convert the chirality of chiral biomolecules into chiroptical signals.

Design and Hybridization Properties of Acyclic Xeno Nucleic Acid Oligomers.

Xeno nucleic acids (XNAs) are analogues of DNA and RNA that have a non-ribose artificial scaffold. XNAs are possible prebiotic genetic carriers as well as alternative genetic systems in artificial life. In addition, XNA oligomers can be used as biological tools. Acyclic XNAs, which do not have cyclic scaffolds, are attractive due to facile their synthesis and remarkably high nuclease resistance. To maximize the performance of XNAs, a negatively charged backbone is preferable to provide sufficient water solubility; however, acyclic XNAs containing polyanionic backbones suffer from high entropy cost upon duplex formation, because of the high flexibility of the acyclic nature. Herein, we review the relationships between the structure and duplex hybridization properties of various acyclic XNA oligomers with polyanion backbones.

Nonenzymatic polymerase-like template-directed synthesis of acyclic L-threoninol nucleic acid.

Evolution of xeno nucleic acid (XNA) world essentially requires template-directed synthesis of XNA polymers. In this study, we demonstrate template-directed synthesis of an acyclic XNA, acyclic L-threoninol nucleic acid (L-aTNA), via chemical ligation mediated by N-cyanoimidazole. The ligation of an L-aTNA fragment on an L-aTNA template is significantly faster and occurs in considerably higher yield than DNA ligation. Both L-aTNA ligation on a DNA template and DNA ligation on an L-aTNA template are also observed. High efficiency ligation of trimer L-aTNA fragments to a template-bound primer is achieved. Furthermore, a pseudo primer extension reaction is demonstrated using a pool of random L-aTNA trimers as substrates. To the best of our knowledge, this is the first example of polymerase-like primer extension of XNA with all four nucleobases, generating phosphodiester bonding without any special modification. This technique paves the way for a genetic system of the L-aTNA world.

Light-Regulated Liquid-Liquid Phase Separation for Spatiotemporal Protein Recruitment and Cell Aggregation.

We have previously shown that the upper critical solution temperature-type thermoresponsive ureido polymers such as polyallylurea and poly(2-ureidoethylmethacrylate) derivatives show liquid-liquid phase separation (LLPS), also known as simple coacervation, under physiological conditions below their phase-separation temperatures (Tp). The addition of the polymer-rich coacervate droplets that result from LLPS to a monolayer cell culture induced aggregation of cells into multicellular spheroids. In this study, we prepared a ureido copolymer, poly(vinylamine-co-vinylurea), with azobenzene substituents (Azo-PVU) and demonstrated light-guided assembly and disassembly of LLPS coacervates. Azo-PVUs with Tp values ranging from 10 to 52 °C were prepared by changing the azobenzene content. Ultraviolet light caused a decrease in the Tp of Azo-PVU because of trans-to-cis photoisomerization of the azobenzene and irradiation with visible light increased the Tp. Thus, LLPS of Azo-PVU was reversibly controlled. The coacervate droplets deposited on a dish surface were immediately dissolved by targeted UV irradiation (owing to a decrease in the Tp). Spatially controlled recruitment of proteins on the dish surface was achieved when protein solution was added to the light-patterned surface. Furthermore, the light-guided deposition of coacervates resulted in the spatiotemporal transformation of monolayer cells to aggregates. This light-controlled LLPS will allow the preparation of novel liquid-based materials for biomolecular and cellular engineering.

Dual Crosslinking Photo-Switches for Orthogonal Photo-Control of Hybridization Between Serinol Nucleic Acid and RNA.

Wavelength-selective photo-regulation by multiple chromophores responding to different wavelengths can expand the variation of photo-manipulating systems. Herein, we report the orthogonal photo-regulation of duplex formation between serinol nucleic acid (SNA) and RNA using light-induced crosslinking reactions mediated by a new photo-reactive nucleobase 8-naphthylvinyladenine (NV A) and previously described 8-pyrenylvinyladenine (PV A). An intrastrand crosslink was induced in an SNA strand containing two adjacent NV A residues by irradiation with 340-405 nm light; the crosslink was reversed by irradiation with ≤300 nm light. In an SNA strand with adjacent NV A and PV A residues, an intrastrand crosslink resulted from irradiation with 405-465 nm light that was reversed by irradiation with ≤340 nm light. Intrastrand photo-crosslinking caused severe destabilization of an SNA/RNA duplex, resulting in dissociation to single strands. Cycloreversion resulted in duplex formation. With these NV A/NV A and NV A/PV A photo-switches, four hybridization states of two SNA/RNA duplexes could be orthogonally photo-controlled by irradiation with a suitable wavelength of light.

Photo-regulated trajectories of gliding microtubules conjugated with DNA.

We regulate the persistency in motion of kinesin-driven microtubules (MTs) simply using a photoresponsive DNA (pDNA) and ultraviolet (UV)-visible light. The path persistence length of MTs, which is a measure of the persistency in their motion, increases and decreases upon illuminating the MTs with UV and visible light respectively. Moreover, pDNA is found to work as a shield for MTs against damage under UV irradiation.

A triplex-forming linear probe for sequence-specific detection of duplex DNA with high sensitivity and affinity.

A triplex-forming oligonucleotide (TFO) linear probe containing perylene derivatives was synthesized. The TFO linear probe formed a remarkably stable triplex with a target DNA duplex, resulting in the light-up of fluorescence emission. The sensitivity was extremely high even at pH 7. Detection of PCR-amplified target DNA was demonstrated.

Incorporation of Pseudo-complementary Bases 2,6-Diaminopurine and 2-Thiouracil into Serinol Nucleic Acid (SNA) to Promote SNA/RNA Hybridization.

Serinol nucleic acid (SNA) is a promising candidate for nucleic acid-based molecular probes and drugs due to its high affinity for RNA. Our previous work revealed that incorporation of 2,6-diaminpurine (D), which can form three hydrogen bonds with uracil, into SNA increases the melting temperature of SNA-RNA duplexes. However, D incorporation into short self-complementary regions of SNA promoted self-dimerization and hindered hybridization with RNA. Here we synthesized a SNA monomer of 2-thiouracil (sU), which was expected to inhibit base pairing with D by steric hindrance between sulfur and the amino group. To prepare the SNA containing D and sU in high yield, we customized the protecting groups on D and sU monomers that can be readily deprotected under acidic conditions. Incorporation of D and sU into SNA facilitated stable duplex formation with target RNA by suppressing the self-hybridization of SNA and increasing the stability of the heteroduplex of SNA and its complementary RNA. Our results have important implications for the development of SNA-based probes and nucleic acid drugs.

Intrastrand backbone-nucleobase interactions stabilize unwound right-handed helical structures of heteroduplexes of L-aTNA/RNA and SNA/RNA.

Xeno nucleic acids, which are synthetic analogues of natural nucleic acids, have potential for use in nucleic acid drugs and as orthogonal genetic biopolymers and prebiotic precursors. Although few acyclic nucleic acids can stably bind to RNA and DNA, serinol nucleic acid (SNA) and L-threoninol nucleic acid (L-aTNA) stably bind to them. Here we disclose crystal structures of RNA hybridizing with SNA and with L-aTNA. The heteroduplexes show unwound right-handed helical structures. Unlike canonical A-type duplexes, the base pairs in the heteroduplexes align perpendicularly to the helical axes, and consequently helical pitches are large. The unwound helical structures originate from interactions between nucleobases and neighbouring backbones of L-aTNA and SNA through CH-O bonds. In addition, SNA and L-aTNA form a triplex structure via C:G*G parallel Hoogsteen interactions with RNA. The unique structural features of the RNA-recognizing mode of L-aTNA and SNA should prove useful in nanotechnology, biotechnology, and basic research into prebiotic chemistry.

A Quencher-Free Linear Probe from Serinol Nucleic Acid with a Fluorescent Uracil Analogue.

With the goal of developing a quencher-free probe composed of an artificial nucleic acid, the fluorescent nucleobase analogue 5-(perylenylethynyl)uracil (Pe U), which was incorporated into totally artificial serinol nucleic acid (SNA) as a substitute for thymine, has been synthesized. In the context of a 12-mer duplex with RNA, these fluorophores reduce duplex stability slightly compared with that of an SNA without Pe U modification; thus suggesting that structural distortion is not induced by the modification. If two Pe Us were incorporated at separate positions in an SNA, the fluorescent emission at λ≈490 nm was clearly enhanced upon hybridization with complementary RNA. A quencher-free SNA linear probe containing three Pe Us, each separated by six nucleobases, has been designed. Detection of target RNA with high sensitivity and discrimination of a single-base mismatch has also been demonstrated.

8-Pyrenylvinyl Adenine Controls Reversible Duplex Formation between Serinol Nucleic Acid and RNA by [2 + 2] Photocycloaddition.

Photocontrol of duplex formation between the totally artificial serinol nucleic acid (SNA) and target RNA was made possible using a photoresponsive nucleobase 8-pyrenylvinyl adenine (PVA). PVA residues in SNA can be induced to undergo intrastrand [2 + 2] photocycloaddition by 455 nm light. Effective cycloreversion of the PVA photodimer results from irradiation with 340 nm light. These reactions occurred in high yield, rapidly, selectively, and reversibly. When the PVA-SNA/RNA duplex was irradiated with 455 nm light, almost complete dissociation of the duplex was attained, and 340 nm light restored duplex formation by cycloreversion. This is the first example of use of photocycloaddition and cycloreversion to photoregulate canonical duplex formation and dissociation reversibly at constant temperature. Thus, SNA bearing PVA residues have potential for use in photocontrollable biological tools targeting endogenous RNAs in cells as well as photodriven SNA machines.

The Use of Serinol Nucleic Acids as Ultrasensitive Molecular Beacons.

Molecular beacons composed of the artificial serinol nucleic acid (SNA) have demonstrated utility as novel fluorescence probes for visualization of RNA in fixed cells using both conventional fluorescence in situ hybridization (FISH) and wash-free FISH protocols. The SNA molecular beacons have higher affinity for target RNA and greater sensitivity than molecular beacons composed of DNA. Here we describe facile synthesis of the SNA using a conventional DNA synthesizer and protocols for purification by PAGE and HPLC as well as methods for use of the SNA molecular beacon in FISH.

Orthogonally Photocontrolled Non-Autonomous DNA Walker.

There is considerable interest in developing progressively moving devices on the nanoscale, with the aim of using them as parts of programmable therapeutics, smart materials, and nanofactories. Present here is an entirely light-induced DNA walker based on orthogonal photocontrol. Implementing two azobenzene derivatives, S-DM-Azo and DM-Azo, enabled precise coordination of strand displacement reactions that powered a biped walker and guided it along a defined track in a non-autonomous way. This unprecedented type of molecular walker design offers high precision control over the movement in back-and-forth directions as desired, and is regulated solely by the sequence of the irradiation wavelengths. This concept may open new avenues for advancing non-autonomous progressive molecular motors, ultimately facilitating their application at the nanoscale.