Biofunctional Chemistry

Advanced Energy Utilization Division Biofunctional Chemistry Research Section

Professor :Takashi MORII
Associate Professor : Eiji NAKATA
Assistant Professor : Shun NAKANO

Our research group is exploring the design and the construction of biomacromolecules "tailored" for pursuing highly efficient energy utilization.

Nanoassembly of enzymes and receptors to realize artificial photosynthesis & metabolic systems

Cellular chemical transformation processes take place in several reaction steps, with multiple enzymes cooperating in specific fashion to catalyze sequential steps of chemical transformations. One is the most popular natural system is photosynthesis system. Such natural systems are effectively reconstructed in vitro when the individual enzymes are placed in their correct relative orientations.
DNA nano-structure such as DNA-origami can be used as "molecular switchboards" to arrange enzymes and other proteins with nanometer- scale precision. A new method was developed based on proteins, to locate specific proteins by means of special "adapters" known as DNA binding proteins. Several different adapters carrying different proteins can bind independently to defined locations on this type of nanostructure. By using the system, nanoassembly of enzymes and receptors will be constructed as the multi-enzymatic reaction system to realize artificial photosynthesis & metabolic systems.


Exploring functional biomacromolecules by using RNP complexes

Design strategies to tailor receptors, sensors and enzymes are explored by utilizing structurally well-defined protein-RNA complexes. Stepwise strategies of the structure-based design, in vitro selection and the chemical modification afford highly specific receptors for biologically important ligands, such as ATP and the phosphorylated tyrosine residue within a defined amino acid sequence.


Exploring functional biomacromolecules by using RNP complexes

Structure-based design provide alternative strategy to construct protein-based biosensors that assess intracellular dynamics of second messengers and metabolites.


Advanced Energy Utilization Division

Junior Associate Professor :Arivazhagan Rajendran

The aim of this research is to construct the supramolecular assemblies of the topologically interlocked components inside a DNA origami. Such assemblies of the functional structures are promising in the fields of molecular switches, motors, sensors, and logic devices.

Nanomolecular fabrication of supramolecular assemblies

DNA molecules are not merely associated with genetics and the carrying of information. They have been used as excellent construction units in structural DNA nanotechnology due to their unique structural motifs and robust physicochemical properties. I have been working on the self-assembly of DNA origami (a method to create nanostructures by folding DNA) nanostructures to create micrometer scale structures that can be used for several applications such as fabrication of nanodevices, analysis of biomolecular reactions, and templates for various applications. Also, I have utilized these nanostructures for the single molecule analysis of various biomolecular reactions, structure and function of DNA and proteins, and enzymes related to biomass energy conversion.
Recently, I have been collaborating with the research groups of Prof. Takashi Morii (IAE, Kyoto University) and Prof. Youngjoo Kwon (Ewha Womans University) for the nanofabrication of the topologically interlocked supramolecular assemblies.
Topologically interesting structures such as Borromean rings, catenanes, rotaxanes, and knots have been prepared by using duplex DNAs. Also, the complexity of the catenane and rotaxane structures were increased by constructing them by the DNA origami method. However, integration of the duplex DNA catenanes and rotaxanes with functional sequences to the relatively larger and complex DNA nanostructures such as DNA origami has not yet been realized. We have successfully fabricated the DNA catenane and rotaxane structures inside a frame-shaped DNA origami. Apart from the applications in nanotechnology, these interlocked structures can be used for the biomolecular analysis, such as enzymatic reactions and drug screening. For example, these topological structures can be used as the potential substrates for the topoisomerase (Topos) enzymes, and screening of Topo inhibitors.
Among the various types of DNA-binding proteins, Topos are quite attractive due to their importance in cancer therapy. Topos regulate the topological problems of DNA that arises due to the intertwined nature of the double helical structure. These enzymes also play an important role in various biological processes such as replication, transcription, recombination, and chromosome condensation and segregation. Topos resolve the topological problems by transiently cleaving the phosphodiester bond, which generates a Topo-DNA cleavage complex. Once the winding stress is resolved, the Topo-mediated DNA break is resealed. This process is critical for the healthy cells to survive and function normally. Failure to reseal the DNA break can ultimately lead to cell death. This Topo-DNA cleavage complex and various other steps (such as binding of Topo to DNA, ATP driven strand passage, strand cleavage by Topo, formation of Topo-DNA cleavage complex, religation of cleaved DNA, and catalytic cycle after DNA cleavage/enzyme turnover) involved in the Topos function are of great interest as potential targets for the development of anticancer drugs. Despite the development of various Topo-inhibitors, the mechanism of action of these anticancer drug molecules is not well known. Thus, to understand the Topos reaction and the mechanism of the inhibitors, it is necessary to develop an elegant method.
Here, we aim to develop a novel method by using our supramolecular assemblies of the catenane and rotaxane inside a DNA origami and high-speed atomic force microscopy (HS-AFM) for the screening of Topo-inhibitors. The formation of the DNA origami frame and the insertion of the catenane and rotaxane structures were characterized. The Topo reactions and the function of Topo-inhibitors are under investigation. Apart from the Topo reactions and inhibitor screening, the supramolecular assemblies of the topologically interlocked components inside a DNA origami are also promising in the fields of molecular switches, motors, sensors, and logic devices.

DNA rotaxane and catenane inside a DNA origami frame

Left: The illustration of the topologically interlocked DNA rotaxane and catenane inside a DNA origami frame. Right: AFM images of the respective structures.


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