Chang Sup Kim

Biomineralization-based conversion of carbon dioxide to calcium carbonate using recombinant carbonic anhydrase

Recently, as a mimic of the natural biomineralization process, the use of carbonic anhydrase (CA), which is an enzyme catalyzing fast reversible hydration of carbon dioxide to bicarbonate, has been suggested for biological conversion of CO(2) to valuable chemicals. While purified bovine CA (BCA) has been used in previous studies, its practical utilization in CO(2) conversion has been limited due to the expense of BCA preparation. In the present work, we investigated conversion of CO(2) into calcium carbonate as a target carbonate mineral by using a more economical, recombinant CA. To our knowledge, this is the first report of the usage of recombinant CA for biological CO(2) conversion. Recombinant α-type CA originating in Neisseria gonorrhoeae (NCA) was highly expressed as a soluble form in Escherichia coli. We found that purified recombinant NCA which showed comparable CO(2) hydration activity to commercial BCA significantly promoted formation of solid CaCO(3) through the acceleration of CO(2) hydration rate, which is naturally slow. In addition, the rate of calcite crystal formation was also accelerated using recombinant NCA. Moreover, non-purified crude recombinant NCA also showed relatively significant ability. Therefore, recombinant CA could be an effective, economical biocatalyst in practical CO(2) conversion system.

A facile and sensitive immunoassay for the detection of alpha-fetoprotein using gold-coated magnetic nanoparticle clusters and dynamic light scattering

A facile and sensitive immunoassay protocol for the detection of alpha-fetoprotein (AFP) was developed using gold-coated iron oxide magnetic nanoclusters and dynamic light scattering (DLS) methods. The increase in the average particle size due to AFP-mediated aggregation was measured using DLS, and the detection limit was better than 0.01 ng mL(-1).

Recombinant mussel adhesive protein fp-5 (MAP fp-5) as a bulk bioadhesive and surface coating material

Mussel adhesive proteins (MAPs) attach to all types of inorganic and organic surfaces, even in wet environments. MAP of type 5 (fp-5), in particular, has been considered as a key adhesive material. However, the low availability of fp-5 has hampered its biochemical characterization and practical applications. Here, soluble recombinant fp-5 is mass-produced in Escherichia coli. Tyrosinase-modified recombinant fp-5 showed ∼1.11 MPa adhesive shear strength, which is the first report of a bulk-scale adhesive force measurement for purified recombinant of natural MAP type. Surface coatings were also performed through simple dip-coating of various objects. In addition, complex coacervate using recombinant fp-5 and hyaluronic acid was prepared as an efficient adhesive formulation, which greatly improved the bulk adhesive strength. Collectively, it is expected that this work will enhance basic understanding of mussel adhesion and that recombinant fp-5 can be successfully used as a realistic bulk-scale bioadhesive and an efficient surface coating material.

Mussel adhesive protein-based whole cell array biosensor for detection of organophosphorus compounds

A whole cell array biosensor for the efficient detection of neurotoxic organophosphate compounds (OPs) was developed through the immobilization of recombinant Escherichia coli cells containing periplasmic-expressing organophosphorus hydrolase (OPH) onto the surface of a 96-well microplate using mussel adhesive protein (MAP) as a microbial cell-immobilizing linker. Both the paraoxon-hydrolyzing activity and fluorescence microscopy analyses demonstrated that the use of MAP in a whole cell biosensor increased the cell-immobilizing efficiency and enhanced the stability of immobilized cells compared to a simple physical adsorption-based whole cell system. Scanning electron microscopic analyses also showed that the E. coli cells were effectively immobilized on the MAP-coated surface without any pretreatment steps. The whole cell array biosensor system, prepared using optimal MAP coating (50 μg/cm(2)) and cell loading (4 OD(600)), detected paraoxon levels as low as 5 μM with high reproducibility, and its quantitative detection range was ~5-320 μM. The MAP-based whole cell array biosensor showed a good long-term stability for 28 day with 80% retained activity and a reusability of up to 20 times. In addition, paraoxon in tap water was also successfully detected without a reduction in sensitivity. Our results indicate that the proposed MAP-based whole cell array system could be used as a potential platform for a stable and reusable whole cell biosensor.

A functional carbohydrate chip platform for analysis of carbohydrate–protein interaction

A carbohydrate chip based on glass or other transparent surfaces has been suggested as a potential tool for high-throughput analysis of carbohydrate-protein interactions. Here we proposed a facile, efficient, and cost-effective method whereby diverse carbohydrate types are modified in a single step and directly immobilized onto a glass surface, with retention of functional orientation. We modified various types of carbohydrates by reductive amination, in which reducing sugar groups were coupled with 4-(2-aminoethyl)aniline, which has di-amine groups at both ends. The modified carbohydrates were covalently attached to an amino-reactive NHS-activated glass surface by formation of stable amide bonds. This proposed method was applied for efficient construction of a carbohydrate microarray to analyze carbohydrate-protein interactions. The carbohydrate chip prepared using our method can be successfully used in diverse biomimetic studies of carbohydrates, including carbohydrate-biomolecule interactions, and carbohydrate sensor chip or microarray development for diagnosis and screening.

A comparative study on antibody immobilization strategies onto solid surface

Antibody immobilization onto solid surface has been studied extensively for a number of applications including immunoassays, biosensors, and affinity chromatography. For most applications, a critical consideration regarding immobilization of antibody is orientation of its antigen-binding site with respect to the surface. We compared two oriented antibody immobilization strategies which utilize thiolated-protein A/G and thiolated-secondary antibody as linker molecules with the case of direct surface immobilization of thiol-conjugated target antibody. Antibody immobilization degree and surface topography were evaluated by surface plasmon resonance and atomic force microscope, respectively. Protein A/G-mediated immobilization strategy showed the best result and secondary antibody-mediated immobilization was the worst for the total immobilization levels of target antibodies. However, when considering real-to-ideal ratio for antigen binding, total target antigen binding levels (oriented target antibody immobilization levels) had the following order: secondary antibody-mediated immobilization>protein A/G-mediated immobilization>direct thiol-conjugated immobilization. Thus, we confirmed that protein A/G- and secondary antibody-mediated strategies, which consider orientation of target antibody immobilization, showed significantly high antigen binding efficiencies compared to direct random immobilization method. Collectively, the oriented antibody immobilization methods using linker materials could be useful in diverse antibody-antigen interaction-involved application fields.

Functional Interaction Analysis of GM1-Related Carbohydrates and Vibrio cholerae Toxins Using Carbohydrate Microarray

The development of analytical tools is important for understanding the infection mechanisms of pathogenic bacteria or viruses. In the present work, a functional carbohydrate microarray combined with a fluorescence immunoassay was developed to analyze the interactions of Vibrio cholerae toxin (ctx) proteins and GM1-related carbohydrates. Ctx proteins were loaded onto the surface-immobilized GM1 pentasaccharide and six related carbohydrates, and their binding affinities were detected immunologically. The analysis of the ctx-carbohydrate interactions revealed that the intrinsic selectivity of ctx was GM1 pentasaccharide ≫ GM2 tetrasaccharide > asialo GM1 tetrasaccharide ≥ GM3trisaccharide, indicating that a two-finger grip formation and the terminal monosaccharides play important roles in the ctx-GM1 interaction. In addition, whole cholera toxin (ctxAB(5)) had a stricter substrate specificity and a stronger binding affinity than only the cholera toxin B subunit (ctxB). On the basis of the quantitative analysis, the carbohydrate microarray showed the sensitivity of detection of the ctxAB(5)-GM1 interaction with a limit-of-detection (LOD) of 2 ng mL(-1) (23 pM), which is comparable to other reported high sensitivity assay tools. In addition, the carbohydrate microarray successfully detected the actual toxin directly secreted from V. cholerae, without showing cross-reactivity to other bacteria. Collectively, these results demonstrate that the functional carbohydrate microarray is suitable for analyzing toxin protein-carbohydrate interactions and can be applied as a biosensor for toxin detection.

Coexpression of molecular chaperone enhances activity and export of organophosphorus hydrolase in Escherichia coli

Periplasmic secretion has been used in attempts to construct an efficient whole‐cell biocatalyst with greatly reduced diffusion limitations. Previously, we developed recombinant Escherichia coli that express organophosphorus hydrolase (OPH) in the periplasmic space using the twin‐arginine translocation (Tat) pathway to degrade environmental toxic organophosphate compounds. This system has the advantage of secreting protein into the periplasm after folding in the cytoplasm. However, when OPH was expressed with a Tat signal sequence in E. coli, we found that the predominant OPH was an insoluble premature form in the cytoplasm, and thus, the whole‐cell OPH activity was significantly lower than its cell lysate activity. In this work, we, for the first time, used a molecular chaperone coexpression strategy to enhance whole‐cell OPH activity by improving the periplasmic translocation of soluble OPH. We found that the effect of GroEL‐GroES (GroEL/ES) assistance on the periplasmic localization of OPH was secretory pathway dependent. We observed a significant increase in the amount of soluble mature OPH when cytoplasmic GroEL/ES was expressed; this increase in the amount of mature OPH might be due to enhanced OPH folding in the cytoplasm. Importantly, the whole‐cell OPH activity of the chaperone–coexpressing cells was ∼5.5‐fold greater at 12 h after induction than that of cells that did not express the chaperone as a result of significant Tat‐based periplasmic translocation of OPH in the chaperone–coexpressing cells. Collectively, these data suggest that molecular chaperones significantly enhance the whole‐cell activity of periplasmic OPH‐secreting cells, yielding an effective whole‐cell biocatalyst system with highly reduced diffusion limitations.

Engineered whole-cell biocatalyst-based detoxification and detection of neurotoxic organophosphate compounds

The development of efficient tools is required for the eco-friendly detoxification and effective detection of neurotoxic organophosphates (OPs). Although enzymes have received significant attention as biocatalysts because of their high specific activity, the uneconomic and labor-intensive processes of enzyme production and purification make their broad use in practical applications difficult. Because whole-cell systems offer several advantages compared with free enzymes, including high stability, a reduced purification requirement, and low preparation cost, they have been suggested as promising biocatalysts for the detoxification and detection of OPs. To develop efficient whole-cell biocatalysts with enhanced activity and a broad spectrum of substrate specificity, several factors have been considered, namely the selected strains, the chosen OP-hydrolyzing enzymes, where enzymes are localized in a cell, and which enhancer will assist the expression, function, and folding of the enzyme. In this article, we review the current investigative progress in the development of engineered whole-cell biocatalysts with excellent OP-hydrolyzing activity, a broad spectrum of substrate specificity, and outstanding stability for the detoxification and detection of OPs.

Recent developments and applications of bioinspired silicification

Bioinspired synthesis of silica has attracted attention from a wide range of researchers as novel route for fabrication of various nanomaterials. Proteins including silaffins and silicateins as well as polyamines from marine diatoms and sponges are key biomolecules in these biomimetic silicification processes. These methods allow silica mineralization from various silica precursors under mild, biologically compatible conditions in an unprecedentedly fast and facile manner. Notably, the silica polycondensation entails the concomitant encapsulation of other molecules in the reaction solutions. Due to the efficient encapsulation and synergetic effects brought by the encapsulated molecules and the characteristics of biomimetic silica synthesis as well as the mechanical and chemical properties of silica itself, the silica- biomolecule nanocomposites have broad applications in biocatalysis, biosensor, and biomedical areas. Introduction and combination of novel template, precursors, inorganics, or enzymes with the previously used strategies will allow construction of more efficient, purpose-optimized silica nanomaterials with controlled size, composition, and morphology.