Bong-Woo Chung

Expression of a functional human interleukin-18 in yeast

The cDNA sequence for mature human interleukin-18 gene (hIL-18) was cloned and then used to transform Saccharomyces cerevisiae. Two different promoters for heterologous expression of hIL-18 were tested: glyceraldehyde-3-phosphate dehydrogenase (GPD) promoter and a yeast hybrid ADH2-GPD promoter consisting of alcohol dehydrogenase II (ADH2) and GPD promoter. Northern blot analysis revealed that, although variation in the expression level of rhIL-18 existed among transformants, the highest expression was obtained by the GPD promoter. Expressed hIL-18 protein (rhIL-18) was successfully secreted into culture medium due to the presence of the signal peptide of rice amylase 1A. It was possible to produce 13 mg of rhIL-18 protein per liter of culture filtrate without any changes in cell growth. Both cell growth and rhIL-18 production reached the peaks after the 3-day cultivation while the accumulation of transgene transcript peaked at 24 h of cultivation. The secreted rhIL-18 had an estimated molecular mass of 18 kDa. The bioassay observing the induction of interferon-γ from the KG-1 cell line indicated that the secreted recombinant rhIL-18 was bioactive and the specific activity of yeast-derived rhIL-18 was enhanced 15 times relative to that of E. coli-derived rhIL-18.

An integrated process for continuous cellulosic bioethanol production

A high-efficiency, integrated bioethanol production process was developed in this study, using Miscanthus as lignocellulosic biomass. The continuous process involved a twin-screw extruder, a pretreated biomass washing/dewatering process, and a saccharification/fermentation process. In addition, the integration process was designed for the reuse of pretreatment solution and the production of highly concentrated bioethanol. Pretreatment was performed with 0.72 M NaOH solution at 95 °C using an 80 rpm twin-screw speed and a flow rate of 90mL/min (18 g/min of raw biomass feeding). Following washing and dewatering steps, the pretreated biomass was subjected to simultaneous saccharification and bioethanol fermentation processes. The maximum ethanol concentration, yield from biomass, and total volume obtained were 59.3 g/L, 89.9%, and 60 L, respectively, using a pretreated biomass loading of 23.1% (w/v) and an enzyme dosage of 30 FPU/g cellulose. The results presented here constitute an important contribution toward the production of bioethanol from Miscanthus.

Melanin reduction by peroxidase activity in lysosome-related organelle extracts from hen egg whites, HeLa cells, and Saccharomyces cerevisiae

Although melanin plays a biological role in the protection of underlying tissues from harmful ultraviolet radiations, yet large amounts of melanin in light-skinned individuals can make them susceptible to skin cancer. In this study, lysosome-related organelles extracts (LOE) from hen egg whites, HeLa cells, and Saccharomyces cerevisiae have been used to lower melanin color intensity. The results show 80% reduction in melanin upon daily treatment with 100 μg LOE for a period of 19 days. Additionally, the treatment with S. cerevisiae LOE showed the best melanin color reduction, which is consistent with the level of peroxidase activity. The treatment of LOE from S. cerevisiae with NH4Cl decreases melanin reduction activity and peroxidase activity compare to LOE from normal S. cerevisiae. Meanwhile, in contrast, the treatment with H2O2 showed a completely contrary pattern. The above results thus indicate that LOEs can be promising agents for use in cosmeceutical skin lightening as well as for the treatment of hyper pigmentation disorders.

Improvement of bacterial hydrogen production by ATP in mixed organic compounds extracted from Rhodobacter sphaeroides aerobically cultured under dark conditions.

The aim of this study was to increase the hydrogen production of recombinant Escherichia coli harboring HupSL hydrogenase by supplementing physiologically activating compounds extracted from Rhodobacter sphaeroides cultured under anaerobic dark condition after treating them with dimethyl sulfoxide, and the 0.5% extracts contained 4×10(-8)M ATP, which was 100-fold higher than that in the extracts from E. coli. In addition, it was found that the hydrogen production from recombinant E. coli harboring HupSL hydrogenase isolated from R. sphaeroides was doubled under anaerobic conditions when it was supplemented by the extracts from R. sphaeroides cultured aerobically in dark conditions, and this also showed consistent pattern with the increased level of HupSL hydrogenase expression. Therefore, we conclude that the mixed organic compounds extracted from R. sphaeroides have an ATP which enhances the hydrogen production by increasing the amount of HupSL hydrogenase.

Corrosion behavior of high-temperature superconductor YBa2Cu3-yAgyO7-x in the presence of water

Because of the presence of water vapor, YBa2Cu3O7-x degrades easily in the atmosphere and thus very difficult to put it to practical use. When Cu is partially substituted with Ag, however, there is not much a decrease in the critical temperature (Tc) : Tc is 89 K compared with 91 K without substitution. Moreover, partial substitution of Ag increases density, hardness, and superconducting particle size and above all improves considerably its stability in water. In this study YBa2Cu3O7-x and YBa2Cu3-yAgyO7-x as a result of a partial substitution of Ag for Cu were synthesized by pyrophoric method. We investigated their stabilities in water by XRD, SEM, and EPMA after immersing samples in distilled water for 3 hours. We can see that YBa2Cu2.94Ag0.06O7-x was the largest particle size and anticorrosion behavior.

Expression of bacterial xylose isomerase in Saccharomyces cerevisiae under galactose supplemented condition

We constructed recombinant Saccharomyces cerevisiae harboring the xylose isomerase (XI) gene isolated from Clostridium phytofermentans to metabolize xylose and use it as a carbon and energy source. In this study, the effect of supplementation using co-substrate such as glucose or galactose on xylose utilization was studied in recombinant S. cerevisiae. Glucose, which is transported with high affinity by the same transport system as is xylose, was not affected by the heterologous expression of XI, thus xylose utilization was not observed in recombinant S. cerevisiae. However, supplemental galactose added to the recombinant S. cerevisiae stimulated xylose utilization as well as the expression of XI protein. Recombinant S. cerevisiae consumed up to 23.48 g/L of xylose when grown in media containing 40 g/L of xylose and supplemented with 20 g/L of galactose. These cells also produced 15.89 g/L of ethanol. Therefore, expression of the bacterial XI in recombinant S. cerevisiae was highly induced by the addition of supplemental galactose as a co-substrate with xylose, and supplemented galactose enabled the yeast strain to grow on xylose and ferment xylose to ethanol.