Mina Okochi

Chaperonin-mediated stabilization and ATP-triggered release of semiconductor nanoparticles

Various properties of semiconductor nanoparticles, including photoluminescence and catalytic activity, make these materials attractive for a range of applications. As nanoparticles readily coagulate and so lose their size-dependent properties, shape-persistent three-dimensional stabilizers that enfold nanoparticles have been exploited. However, such wrapping approaches also make the nanoparticles insensitive to external stimuli, and so may limit their application. The chaperonin proteins GroEL (from Escherichia coli) and T.th (‘T.th cpn’, from Thermus thermophilus HB8) encapsulate denatured proteins inside a cylindrical cavity; after refolding, the encapsulated proteins are released by the action of ATP inducing a conformational change of the cavity. Here we report that GroEL and T.th cpn can also enfold CdS semiconductor nanoparticles, giving them high thermal and chemical stability in aqueous media. Analogous to the biological function of the chaperonins, the nanoparticles can be readily released from the protein cavities by the action of ATP. We expect that integration of such biological mechanisms into materials science will open a door to conceptually new bioresponsive devices.

TiO2-Mediated Photochemical Disinfection of Escherichia coli Using Optical Fibers.

We have constructed a system for photochemical disinfection of bacteria using a suspension of titanium dioxide and diffuse-light emitting optical fibers (DLEOFs). Disinfection of bacteria at high TiO 2 concentrations was light-limited when conventional optical fibers were used to supply light to the cell suspension. However, when using DLEOFs that emit light laterally from their surface, light distribution throughout a suspension of Escherichia coli was greatly improved even in the presence of high TiO 2 concentrations. A 4-fold increase in photochemical disinfection was obtained at high TiO 2 concentrations using DLEOFs rather than conventional optical fibers for light supply. The use of DLEOFs should provide a generally applicable method for photodisinfection of water supplies.

Prevention of marine biofouling using a conductive paint electrode

Conductive paint electrode was used for marine biofouling on fishing nets by electrochemical disinfection. When a potential of 1.2 V vs. a saturated calomel electrode (SCE) was applied to the conductive paint electrode, Vibrio alginolyticus cells attached on the electrode were completely killed. By applying a negative potential, the attached cells were removed from the surface of the electrode. Changes in pH and chlorine concentration were not observed at potentials in the range -0.6 approximately 1.2 V vs. SCE. In a field experiment, accumulation of the bacterial cells and formation of biofilms on the electrode were prevented by application of an alternating potential, and 94% of attachment of the biofouling organisms was inhibited electrically on yarn used for fishing net coated with conductive paint. Copyright 1998 John Wiley & Sons, Inc.

Facilitated release of substrate protein from prefoldin by chaperonin

Prefoldin is a chaperone that captures a protein‐folding intermediate and transfers it to the group II chaperonin for correct folding. However, kinetics of interactions between prefoldin and substrate proteins have not been investigated. In this study, dissociation constants and dissociation rate constants of unfolded proteins with prefoldin were firstly measured using fluorescence microscopy. Our results suggest that binding and release of prefoldin from hyperthermophilic archaea with substrate proteins were in a dynamic equilibrium. Interestingly, the release of substrate proteins from prefoldin was facilitated when chaperonin was present, supporting a handoff mechanism of substrate proteins from prefoldin to the chaperonin.

TiN electrode reactor for disinfection of drinking water

Abstract Titanium nitride (TiN) is a biocompatible material and has very low electrical resistance. Electrochemical control of pathogenic microbes derived from a drinking water distribution system was investigated using a TiN electrode. When a potential of 1.2xa0V vs saturated calomel electrode (SCE) was applied, the survival ratio of microorganisms decreased to below 40%. Changes in pH were not observed at 1.2xa0V vs SCE. Also, by applying −0.6xa0V vs SCE for 30xa0min, 69% of cells on the electrode surface were detached by the electrostatic repulsion. Therefore, an electrochemical disinfection reactor using a TiN mesh as the working electrode and the counter electrode was constructed. The drinking water containing mean viable cell concentration of 73 cells/ml was continuously passed through the reactor at a flow rate of 15xa0ml/min. The viable cell concentration in treated water decreased to below 5 cells/ml. When no potential was applied, cell concentration in treated water gradually increased after 200xa0h of reactor operation. In contrast, when alternating potentials of 1.2 and −0.6xa0V vs silver/silver chloride (Ag/AgCl) were applied to the TiN mesh working electrode, the viable cell concentration remained below 100 cells/ml during a 440xa0h operation. The reactor for drinking water disinfection incorporated with the TiN mesh electrode worked effectively by applying alternating potentials of 1.2 and −0.6xa0V vs Ag/AgCl.

Molecular characterization of the group II chaperonin from the hyperthermophilic archaeum Pyrococcus horikoshii OT3

The group II chaperonin from the hyperthermophilic archaeum Pyrococcus horikoshii OT3 (PhCPN) and its functional cooperation with the cognate prefoldin were investigated. PhCPN existed as a homo-oligomer in a double-ring structure, which protected the citrate synthase of a porcine heart from thermal aggregation at 45°C, and did the same on the isopropylmalate dehydrogenase (IPMDH) of a thermophilic bacterium, Thermus thermophilus HB8, at 90°C. PhCPN also enhanced the refolding of green fluorescent protein (GFP), which had been unfolded by low pH, in an ATP-dependent manner. Unexpectedly, functional cooperation between PhCPN and Pyrococcus prefoldin (PhPFD) in the refolding of GFP was not observed. Instead, cooperation between PhCPN and PhPFD was observed in the refolding of IPMDH unfolded with guanidine hydrochloride. Although PhCPN alone was not effective in the refolding of IPMDH, the refolding efficiency was enhanced by the cooperation of PhCPN with PhPFD.

Electrochemical disinfection of drinking water using an activated-carbon-fiber reactor capable of monitoring its microbial fouling

Abstract An electrochemical reactor employing activated carbon fibers (ACF) was constructed for the disinfection of bacteria in drinking water. The application of an alternating potential of 1.0 V and −0.8 V versus a saturated calomel electrode, for disinfecting and desorbing bacteria, enabled reactor operation for 840u2009h. Drinking water was passed through the reactor in stop/flow mode: 300u2009ml/min flow for 12u2009h and no flow for 12u2009h, alternately. The bacterial cell density in treated water was always been less than 20 cells/ml. It was also found that the formation of biofilm on the ACF reactor caused an increase in current, enabling the self-detection of microbial fouling.

Electrochemical sterilization of bacteria using a graphite electrode modified with adsorbed ferrocene

Electrochemical sterilization of the marine gram-negative bacterium Vibrio alginolyticus cells was carried out using basal-plane pyrolytic graphite electrode modified with adsorbed ferrocene. When cyclic voltammetry was taken in V. alginolyticus cell suspension using an electrode modified with ferrocene at a scan rate of 20 mV per s at 25 °C, an electrocatalytic oxidation occurred above 0.1 V versus saturated calomel electrode (sce). Peak current was observed around 0.3 V vs sce. The bacteria which attached to the ferrocene modified electrode were sterilized at 0.2 V vs sce in sterile seawater, whereas they were sterilized at 0.8 V vs sce when using a bare graphite electrode. This sterilization was due to the electrochemical oxidation of the intracellular substance and not to the toxicity of ferrocene. V. alginolyticus cells in sterile seawater were completely sterilized after 10 min by applying 0.2 V vs sce.

Electrochemical detection of allergen in small-volume whole blood using an array microelectrode: A simple method for detection of allergic reaction

A safe, simplified, and rapid method for detection of allergen has been developed. Serotonin, a chemical mediator secreted during an allergic reaction, was used as a marker in electrochemical detection. A 20-microL drop of whole blood was used for the electrochemical detection of allergen using an array microelectrode. When cyclic voltammetry was carried out on whole blood samples containing 1 microg/mL serotonin, an anodic peak current appeared at around 350 mV versus a silver/silver chloride electrode using a Nafion-coated array microelectrode. Allergen was selectively detected using whole blood samples by applying a constant potential of 350 mV after 40 min incubation with addition of allergen. The results obtained by the electrochemical detection method correlated well with the diagnosis obtained from the amount of IgE antibody.

Electrochemical killing of microorganisms using the oxidized form of ferrocenemonocarboxylic acid

Electrochemical killing of Escherichia coli cells was carried out using oxidized form of ferrocenemonocarboxylic acid (FCA) dissolved in 0.1 M phosphate buffer (pH 7.0). Cyclic voltammetry of 0.25 mM FCA was performed with the addition of coenzyme A (CoA), that is considered to be the main contributor of the anodic peak current appeared at around 0.7 V vs saturated calomel electrode in cyclic voltammogram of microorganisms. Electrocatalytic oxidation of CoA was observed at around 0.3 V. Also, the electrocatalytic oxidation wave was confirmed when cyclic voltammetry was performed in 0.25 mM FCA containing 1.7 x 10 11 E. coli cells/ml. Electrochemical killing of E. coli was examined by applying constant potentials in 0.5 mM FCA. The survival ratio decreased to below 5% at low potential of 0.4 V in 0.5 mM FCA compared to 0.7 V in the buffer. The decrease in survival ratio was also observed with the gram-positive bacterium, Bacillus subtilis and an eucaryote cell, Saccharomyces cerevisiae. When E. coli cell suspension was added to 0.5 mM FCA, oxidized by applying 1.0 V for 60 min, the decrease in survival ratio was observed. In contrast, decrease in survival ratio was not observed when cell suspension was added in FCA without electrolysis. E. coli cells were shown to be killed by the contact with oxidized form of FCA.