Shunsuke Tomita

Bio: Shunsuke Tomita is an academic researcher from National Institute of Advanced Industrial Science and Technology. The author has contributed to research in topics: Medicine & Protein aggregation. The author has an hindex of 15, co-authored 44 publications receiving 574 citations. Previous affiliations of Shunsuke Tomita include Applied Science Private University & University of Tsukuba.

Regulation of lysozyme activity based on thermotolerant protein/smart polymer complex formation.

Abstract: Proteins have evolved to acquire highly specialized biological functions and are ideal for various applications in both medicine and biotechnology, although denaturation is one of the major problems in protein chemistry. Here, we show a novel strategy for the regulation and preservation of the enzymatic activity even after heat treatment by the complex formation with a cationic smart copolymer, poly(N,N-diethylaminoethyl methacrylate)-graft-poly(ethylene glycol) (PEAMA-g-PEG). PEAMA-g-PEG suppressed the enzymatic activity of lysozyme completely without any conformational change, indicating complex formation and the capping of the active site of lysozyme by PEAMA-g-PEG. The addition of an anionic polymer, poly(acrylic acid) (PAAc), recovered the inhibited enzymatic activity of the lysozyme/PEAMA-g-PEG complex completely. Surprisingly, even after heating the lysozyme with PEAMA-g-PEG for 20 min at 98 degrees C, the addition of PAAc recovered 80% enzymatic activity of lysozyme. Circular dichroism (CD) spectral analysis clearly indicated that the irreversible inactivation of lysozyme induced by the heat treatment was suppressed by the complex formation with PEAMA-g-PEG.

Enzyme Hyperactivation System Based on a Complementary Charged Pair of Polyelectrolytes and Substrates

Abstract: Artificial enzyme activators are of great interest for enzyme applications in a wide range of research fields. Here, we report an enzyme hyperactivation system using polyelectrolytes that are complementary to charged substrates. The enzyme activity of α-chymotrypsin (ChT) for a cationic substrate increased 7-fold at pH 7.0 in the presence of anionic poly(acrylic acid) (PAAc) and for an anionic substrate increased 18-fold at pH 7.0 in the presence of cationic poly(allylamine) (PAA). Analysis of salt and pH effects, enzyme kinetics, dynamic light scattering (DLS), and circular dichroism (CD) indicated that the enzyme activation results from favorable electrostatic interactions between oppositely charged substrates and polyelectrolytes surrounding the enzymes. This hyperactivation system does not require laborious mutagenesis or chemical modification of enzymes and thus is relevant to a number of applications.

Improved complementary polymer pair system: switching for enzyme activity by PEGylated polymers.

Abstract: The development of technology for on/off switching of enzyme activity is expected to expand the applications of enzyme in a wide range of research fields. We have previously developed a complementary polymer pair system (CPPS) that enables the activity of several enzymes to be controlled by a pair of oppositely charged polymers. However, it failed to control the activity of large and unstable α-amylase because the aggregation of the complex between anionic α-amylase and cationic poly(allylamine) (PAA) induced irreversible denaturation of the enzyme. To address this issue, we herein designed and synthesized a cationic copolymer with a poly(ethylene glycol) backbone, poly(N,N-diethylaminoethyl methacrylate)-block-poly(ethylene glycol) (PEAMA-b-PEG). In contrast to PAA, α-amylase and β-galactosidase were inactivated by PEAMA-b-PEG with the formation of soluble complexes. The enzyme/PEAMA-b-PEG complexes were then successfully recovered from the complex by the addition of anionic poly(acrylic acid) (PAAc). Thus, dispersion of the complex by PEG segment in PEAMA-b-PEG clearly plays a crucial role for regulating the activities of these enzymes, suggesting that PEGylated charged polymer is a new candidate for CPPS for large and unstable enzymes.

Arginine controls heat‐induced cluster–cluster aggregation of lysozyme at around the isoelectric point

Abstract: The process of protein aggregation has attracted a great deal of research attention, as aggregates are first of all a nuisance to preparation of high quality protein and secondly used as novel materials. In the latter case, the process of protein aggregation needs to be controlled. Here, we show how arginine (Arg) regulates the process of heat-induced protein aggregation. Dynamic light scattering and transmission electron microscopy revealed that heat-induced aggregation of lysozyme at around the isoelectric point occurred in a two-step process: formation of start aggregates, followed by further growth mediated by their sticking with diffusion-limited cluster-cluster aggregation. In the presence of Arg, the diffusion-limited regime changed to reaction-limited cluster-cluster aggregation. The data indicated that the solution additives that coexisted with proteins would affect the property of the formed product, such as morphology and mechanic strength.

Using Multivariate Statistics

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Supramolecular Hydrogelators and Hydrogels: From Soft Matter to Molecular Biomaterials

Abstract: In this review we intend to provide a relatively comprehensive summary of the work of supramolecular hydrogelators after 2004 and to put emphasis particularly on the applications of supramolecular hydrogels/hydrogelators as molecular biomaterials. After a brief introduction of methods for generating supramolecular hydrogels, we discuss supramolecular hydrogelators on the basis of their categories, such as small organic molecules, coordination complexes, peptides, nucleobases, and saccharides. Following molecular design, we focus on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators. Particularly, we discuss the applications of supramolecular hydrogelators after they form supramolecular assemblies but prior to reaching the critical gelation concentration because this subject is less explored but may hold equally great promise for helping ...

The Optoelectronic Nose: Colorimetric and Fluorometric Sensor Arrays.

Abstract: A comprehensive review on the development and state of the art of colorimetric and fluorometric sensor arrays is presented Chemical sensing aims to detect subtle changes in the chemical environment by transforming relevant chemical or physical properties of molecular or ionic species (ie, analytes) into an analytically useful output Optical arrays based on chemoresponsive colorants (dyes and nanoporous pigments) probe the chemical reactivity of analytes, rather than their physical properties (eg, mass) The chemical specificity of the olfactory system does not come from specific receptors for specific analytes (eg, the traditional lock-and-key model of substrate-enzyme interactions), but rather olfaction makes use of pattern recognition of the combined response of several hundred olfactory receptors In a similar fashion, arrays of chemoresponsive colorants provide high-dimensional data from the color or fluorescence changes of the dyes in these arrays as they are exposed to analytes This provides chemical sensing with high sensitivity (often down to parts per billion levels), impressive discrimination among very similar analytes, and exquisite fingerprinting of extremely similar mixtures over a wide range of analyte types, in both the gas and liquid phases Design of both sensor arrays and instrumentation for their analysis are discussed In addition, the various chemometric and statistical analyses of high-dimensional data (including hierarchical cluster analysis (HCA), principal component analysis (PCA), linear discriminant analysis (LDA), support vector machines (SVMs), and artificial neural networks (ANNs)) are presented and critiqued in reference to their use in chemical sensing A variety of applications are also discussed, including personal dosimetry of toxic industrial chemical, detection of explosives or accelerants, quality control of foods and beverages, biosensing intracellularly, identification of bacteria and fungi, and detection of cancer and disease biomarkers

A review on graphene-based nanocomposites for electrochemical and fluorescent biosensors

Abstract: Biosensors with high sensitivity, selectivity and a low limit of detection, reaching nano/picomolar concentrations of biomolecules, are important to the medical sciences and healthcare industry for evaluating physiological and metabolic parameters. Over the last decade, different nanomaterials have been exploited to design highly efficient biosensors for the detection of analyte biomolecules. The discovery of graphene has spectacularly accelerated research on fabricating low-cost electrode materials because of its unique physical properties, including high specific surface area, high carrier mobility, high electrical conductivity, flexibility, and optical transparency. Graphene and its oxygenated derivatives, including graphene oxide (GO) and reduced graphene oxide (rGO), are becoming an important class of nanomaterials in the field of biosensors. The presence of oxygenated functional groups makes GO nanosheets strongly hydrophilic, facilitating chemical functionalization. Graphene, GO and rGO nanosheets can be easily combined with various types of inorganic nanoparticles, including metals, metal oxides, semiconducting nanoparticles, quantum dots, organic polymers and biomolecules, to create a diverse range of graphene-based nanocomposites with enhanced sensitivity for biosensor applications. This review summarizes the advances in two-dimensional (2D) and three-dimensional (3D) graphene-based nanocomposites as emerging electrochemical and fluorescent biosensing platforms for the detection of a wide range of biomolecules with enhanced sensitivity, selectivity and a low limit of detection. The biofunctionalization and nanocomposite formation processes of graphene-based materials and their unique properties, surface functionalization, enzyme immobilization strategies, covalent immobilization, physical adsorption, biointeractions and direct electron transfer (DET) processes are discussed in connection with the design and fabrication of biosensors. The enzymatic and nonenzymatic reactions on graphene-based nanocomposite surfaces for glucose- and cholesterol-related electrochemical biosensors are analyzed. This review covers a very broad range of graphene-based electrochemical and fluorescent biosensors for the detection of glucose, cholesterol, hydrogen peroxide (H2O2), nucleic acids (DNA/RNA), genes, enzymes, cofactors nicotinamide adenine dinucleotide (NADH) and adenosine triphosphate (ATP), dopamine (DA), ascorbic acid (AA), uric acid (UA), cancer biomarkers, pathogenic microorganisms, food toxins, toxic heavy metal ions, mycotoxins, and pesticides. The sensitivity and selectivity of graphene-based electrochemical and fluorescent biosensors are also examined with respect to interfering analytes present in biological systems. Finally, the future outlook for the development of graphene based biosensing technology is outlined.