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Soichi Arai

Publications and source records attributed to Soichi Arai.

18 recordsLinked to original sources
PubMed2006

Purification and characterization of an alpha-amylase of Pichia burtonii isolated from the traditional starter "murcha" in Nepal.

Among more than 20 yeast strains isolated from the traditional starter "murcha" in Nepal, we characterized a yeast that might be involved in saccharification. This strain, identified as Pichia burtonii, produced an extracellular amylolytic enzyme when cultured in the presence of starch in the medium. Since no amylase secreted by P. burtonii has yet been reported, we purified the enzyme and determined its N-terminal amino acid sequence. Together with the results of a hydrolyzing activity assay toward various substrates, it was found to be an alpha-amylase. The purified enzyme, named Pichia burtonii alpha-amylase (PBA), was a glycoprotein with an apparent molecular mass of 51 kDa. Enzyme activity was optimal at pH 5.0 at 40 degrees C. The enzyme retained 80% of its original activity after incubation under the optimal pH condition at 50 degrees C for 30 min. The activity was inhibited by metal ions such as Cd(2+), Cu(2+), Hg(2+), Al(3+), and Zn(2+).

Amino Acid Sequence↗
PubMed2006

Neoculin, a taste-modifying protein, is recognized by human sweet taste receptor.

Neoculin, a sweet protein occurring in Curculigo latifolia, is unique in that it also has taste-modifying activity capable of converting sourness to sweetness. Calcium imaging analysis with HEK cells expressing the human sweet taste receptor, hT1R2/T1R3 demonstrated that the intracellular calcium concentration increased following the addition of 20 microM neoculin. The use of lactisole, a blocker of hT1R3, inhibited the intracellular calcium concentration increase almost completely. In sensory tests, when acetate buffers with different pH values were placed on the tongue after tasting neoculin, a higher intensity of sweetness was detected at lower pH. The sweetness was also suppressed with the addition of lactisole. These results suggest that both the sweetness and the taste-modifying activity are mediated via the human sweet taste receptor.

Benzene Derivatives↗
PubMed2006

Safety evaluation of hypoallergenic wheat flour by using a DNA microarray.

The effect of the consumption of hypoallergenic wheat flour (HWF) on the expression of a wide spectrum of genes was analyzed by using a DNA microarray. Gene expression profiles in the liver and intestines of rats fed on a diet composed mainly of HWF were compared with those of rats fed on a normal flour-based diet. Among the eight thousand transcripts represented on the GeneChip microarray, no more than 30 genes exhibited up- or down-regulation of two-fold or more after one week or two months of HWF consumption. No adverse effects were apparent. Up-regulation of some of the genes known to respond to the interferon-gamma signal was apparent in the one-week experiment, which may be related to possible oral immunotolerance resulting from HWF feeding. This DNA microarray technology presents an efficient method for evaluating the safety of foods.

Allergens↗
PubMed2006

Crystal structure of neoculin: insights into its sweetness and taste-modifying activity.

Although the majority of sweet compounds are of low molecular mass, several proteins are known to elicit sweet taste responses in humans. The fruit of Curculigo latifolia contains a heterodimeric protein, neoculin, which has both sweetness and a taste-modifying activity that converts sourness to sweetness. Here, we report the crystal structure of neoculin at 2.76A resolution. This is the first well-defined tertiary structure of a taste-modifying protein of this kind. The overall structure is quite similar to those of monocot mannose-binding lectins. However, crucial topological differences are observed in the C-terminal regions of both subunits. In both subunits of neoculin, the C-terminal tails turn up to form loops fixed by inter-subunit disulfide bonds that are not observed in the lectins. Indeed, the corresponding regions of the lectins stretch straight over the surface of another subunit. Such a C-terminal structural feature as is observed in neoculin results in a decrease in subunit-subunit interactions. Moreover, distribution of electrostatic potential on the surface of neoculin is unique and significantly different from those of the lectins, particularly in the basic subunit (NBS). We have found that there is a large cluster composed of six basic residues on the surface of NBS, and speculate that it might be involved in the elicitation of sweetness and/or taste-modifying activity of neoculin. Molecular dynamics simulation based on the crystallography results suggests that neoculin may adopt a widely "open" conformation at acidic pH, while unprotonated neoculin at neutral pH is in a "closed" conformation. Based on these simulations and the generation of a docking model between neoculin and the sweet-taste receptor, T1R2-T1R3, we propose the hypothesis that neoculin is in dynamic equilibrium between open and closed states, and that the addition of an acid shifts the equilibrium to the open state, allowing ligand-receptor interaction.

Amino Acid Sequence↗
PubMed2006

Extracellular production of neoculin, a sweet-tasting heterodimeric protein with taste-modifying activity, by Aspergillus oryzae.

Neoculin (NCL), a protein with sweetness approximately 500-fold that of sugar, can be utilized as a nonglycemic sweetener. It also has taste-modifying activity to convert sourness to sweetness. NCL is a heterodimer composed of an N-glycosylated acidic subunit (NAS) and a basic subunit (NBS), which are conjugated by disulfide bonds. For the production of recombinant NCL (rNCL) by Aspergillus oryzae, alpha-amylase with a KEX2 cleavage site, -K-R-, was fused upstream of each of NAS and NBS and the resulting fusion proteins were simultaneously expressed. For accurate and efficient cleavage of the fusion construct by KEX2-like protease, a triglycine motif was inserted after the KEX2 cleavage site. As NBS showed lower production efficiency than did NAS, a larger amount of the NBS expression plasmid than of NAS expression plasmid was introduced during cotransformation, resulting in successful production of rNCL in the culture medium. Moreover, to obtain a higher production yield of rNCL, the active form of hacA cDNA encoding a transcription factor that induces an unfolded protein response was cloned and expressed constitutively. This resulted in a 1.5-fold increase in the level of rNCL production (2.0 mg/liter). rNCL was purified by chromatography, and its NAS was found to be N-glycosylated as expected. The original sweetness and taste-modifying activity of rNCL were comparable to those of native NCL when confirmed by calcium imaging with human embryonic kidney cells expressing the human sweet taste receptor and by sensory tests.

Aspergillus oryzae↗
PubMed2006

[Molecular logic of alcohol and taste].

Ethanol, a main constituent of every alcohol beverage, has long been calling our attention to its gustatory effect. Recent molecular dynamics studies have suggested that ethanol as well as other tastants in foods, when taken in the oral cavity, gives rise to a taste signal which is expressed via reception at taste cells in the taste bud, intracellular signal transduction in collaboration with G proteins and effecters, and signal transmission to synapsed taste neurons, and/or simultaneous reception at and signal transduction in somatosensory neurons. The taste of ethanol and its acceptability are then recognized and judged at the higher center, with generation of various physiological phenomena in the body. We have tried to make an all-inclusive DNA microarray analysis, demonstrating that when a rat tongue is stimulated with a drop of aqueous ethanol in vivo, several particular genes are specifically up- or down-regulated in trigeminal ganglions. These initial gene expression changes at peripheral neurocytes might in whole or in part trigger some of the ethanol-associated gustatory and bodily response. The importance of defining a related molecular logic is emphasized to understand academic and industrial significances of this unique food constituent, ethanol.

Alcoholic Beverages↗
PubMed2005

Intake of soy protein isolate alters hepatic gene expression in rats.

Soy protein isolate (SPI) can elicit various physiological effects such as cholesterol lowering and antiobesity effects. To examine whether hepatic gene expression is altered by SPI intake, rats were fed an SPI or casein diet for 8 weeks. After 8 weeks of feeding, liver weight and plasma triglyceride and cholesterol levels were significantly lower in the SPI group than in the casein group. Hepatic gene expression was investigated using DNA microarrays. The expression profiles and statistical analysis showed clear and significant differences between the SPI and casein groups (p < 0.05); in the SPI group, 63 genes were up-regulated and 57 genes were down-regulated, most involved in various physiological functions such as lipid metabolism, antioxidant activity, transcriptional regulation, and energy metabolism. Especially in lipid metabolism, the down-regulated genes are related to fatty acid synthesis and the up-regulated genes are related to cholesterol synthesis and steroid catabolism. These results suggest that SPI intake could maintain homeostasis primarily by modulating lipid and energy metabolism.

Animals↗
PubMed2005

A nutrigenomics database--integrated repository for publications and associated microarray data in nutrigenomics research.

In the current situation where microarray data in the field of nutritional genomics (nutrigenomics) are accumulating rapidly, there is imminent need for an efficient data infrastructure to support research workflow. We have established a web-based, integrated database of the publications and microarray expression data in the field of nutrigenomics. The registered data include links to external databases such as PubMed of the National Center for Biotechnology Information and public microarray databases that contain Minimum Information About a Microarray Experiment-compliant microarray expression data. Using this database, all data sets created will be effectively utilized and shared with other researchers. This database is built on an open-source database system and is freely accessible via the World Wide Web (http://a-yo5.ch.a.u-tokyo.ac.jp/index.phtml).

Databases, Genetic↗
PubMed2004

Identification of candidate genes involved in somatosensory functions of cranial sensory ganglia.

We have shown that the characteristics of tissue trees obtained by the hierarchical cluster analysis of DNA microarray data suggest the cellular expression patterns of genes in the gene clusters [J. Neurosci. Res. 74 (2003) 818]. We here identified three gene clusters containing 11 genes as a potential pool of candidate genes related to somatosensation in cranial structures such as the face, oral cavity and pharynx. To obtain the cellular expression profiles, eight genes other than three genes analyzed previously were subjected to in situ hybridization analysis. The results show that all of the 11 profiles are roughly similar and suggest that the positive cells are probably somatosensory neurons in two cranial sensory ganglia, the trigeminal and petrosal ganglia. The expression profiles and probable physiological functions of the 6 genes such as trkA, NaN and galanin suggest their direct involvement in specific somatosensory functions such as nociception. The function of another gene, calretinin, is putatively related to mechanosensation and proprioception. The roles of the remaining four genes, including aquaporin 1 and two EST clones, in sensory neurons are unknown, and may provide clues to understand the sensory function in TG and PG.

Animals↗
PubMed2004

DNA microarray analyses of the effects of dietary proteins.

Dietary proteins and amino acids serve not only as a building block for body components but also as regulators of a variety of body functions. A great many of the functions of ingested proteins, their peptide fragments, and amino acids have been characterized and some have been brought to practical application. Using a GeneChip DNA microarray system, we first compared the gene expression profiles among rats fed on 12% casein, 12% gluten, and protein-free diets for one week. The results revealed that a few hundred genes in the liver and muscle were up- or down-regulated by more than two-fold after feeding of the gluten or the protein-free diet. Interesting findings included the induction of genes for synthesis and catabolism of cholesterol by gluten feeding. In addition, we performed a study to examine the effect of the consumption of an enzymatically produced, hypoallergenic wheat flour on gene expression profiles in rats. The results confirmed the safety of this novel food product.

Animals↗
PubMed2004

Gene expression profiling of cranial sensory ganglia that transmit food intake stimuli.

Peripheral cranial sensory nerves projecting into the oral cavity receive food intake stimuli and transmit sensory signals to the central nervous system. They are derived from four cranial sensory ganglia, trigeminal, geniculate, petrosal, and nodose ganglia, each of which contains multiple kinds of sensory neurons with different cell morphologies and neuronal properties. We investigated the complex properties of these neurons from the viewpoint of gene expression using DNA microarrays. The 498 genes were selected from a total of 8,740 genes as showing tissue-dependent expression on the microarray by hierarchical cluster analysis, in which several genes known to be differentially expressed in cranial sensory ganglia are included. This suggests that DNA microarray cluster analysis revealed a number of characteristic genes for sensory neurons in these ganglia. Among the selected 498 genes, 44 genes are associated with neurotransmission, such as neuropeptides, their receptors, and vesicle transport, and 26 are ion channels regulating membrane potentials. The identification of a number of genes related directly to neural properties indicates that these sensory ganglia contain heterogeneous types of neurons with different neural properties.

Animals↗
PubMed2004

Gene cloning and characterization of a Bacillus vietnamensis metalloprotease.

A Bacillus vietnamensis metalloprotease (BVMP) with high affinity toward collagen was isolated and purified from the culture supernatant of Bacillus vietnamensis 11-4 occurring in Vietnamese fish sauces. The BVMP gene was cloned and its nucleotide and coded amino acid sequences determined. BVMP consists of 547 amino acid residues, with the zinc-binding sites conserved in common metalloproteases. It shares 57% amino acid identity with thermolysin originating from Bacillus thermoproteolyticus. The three-dimensional structure of BVMP was deduced by computer-aided modeling with the use of the known three-dimensional thermolysin structure as a template. Like thermolysin, BVMP cleaved the oxidized insulin B-chain at the peptide bonds involving the N-terminal sides of hydrophobic and aromatic amino acids. BVMP also showed high hydrolytic activity toward gelatin, collagen, casein, and elastin, especially toward the skeletal proteins at increased NaCl concentration. The high activity was found to be due to enhanced affinity to the substrates. Kinetical data on BVMP indicated that the Km values for the hydrolysis of Cbz-GPGGPA as a collagen model decreased as the concentration of added NaCl increased. Some contribution of this enzyme during the aging of fish sauces at high salt concentrations can thus be expected.

Amino Acid Sequence↗
PubMed2003

DNA microarray cluster analysis reveals tissue similarity and potential neuron-specific genes expressed in cranial sensory ganglia.

Each of four cranial sensory ganglia, trigeminal, geniculate, petrosal, and nodose ganglia, contains multiple kinds of sensory neurons with different cell morphologies and neuronal properties that transmit information about sensory stimuli received peripherally. Here we analyze the complex properties of these neurons from the viewpoint of gene expression using DNA microarrays by cluster analysis. From a total of 8,740 genes, 498 genes were selected as showing tissue-dependent expression on the microarray by hierarchical cluster analysis, and their profiles indicated that, among the four sensory ganglia, the petrosal and trigeminal ganglia are intimately related. Tissue trees of 37 subclusters containing the 498 genes showed that the profiles of gene expression and the subclusters were classified into a smaller number of groups (18 groups) when information on the amounts of expression was added. In situ hybridization analysis of 21 genes selected from 13 different groups was carried out, and the gene expression patterns were classified into eight categories. The putative profiles postulated from the microarray data were essentially consistent with the patterns of expression at the cellular level as shown by in situ hybridization. In conclusion, from the overall analyses of gene expression by DNA microarray, we can identify a number of candidate genes showing neuron type-specific expression in the peripheral ganglia.

Animals↗
PubMed2002

Plant seed cystatins and their target enzymes of endogenous and exogenous origin.

Cystatins are protein inhibitors of cysteine proteinases of the papain family, and those of animal origin have long been studied from medical and physiological aspects. In the meantime, oryzacystatin cloned from rice seeds in 1987 was recognized as the first well-defined cystatin of plant origin. Cloning studies followed to disclose various plant cytstatins including those of corn and soybean origin, their similarities to and differences from animal cystatins being analyzed in detail. Plant seed cystatins are now understood as factors controlling germination by inhibition of endogenous cysteine proteinases. They can also recognize insect midgut proteinases as exogenous target enzymes to control. This paper discusses chemical and phytophysiological relationships between cystatins and their targets.

Amino Acid Sequence↗
PubMed2002

Dietary protein quantity and quality affect rat hepatic gene expression.

To gain a comprehensive understanding of the molecular mechanisms underlying the effects of dietary protein on alternations in physiologic and pathologic status, the GeneChip microarray system was used to investigate the consequences of two different states of protein malnutrition on gene expression in rat liver. Expressions of 281 genes were increased or decreased by twofold or more by treatment with a protein-free diet for 1 wk compared with control rats fed a casein diet. Similarly, 111 genes were affected in rats fed a wheat gluten diet compared with those fed the casein diet. Although some of the genes identified were known to respond to protein nutrition, a majority were newly identified as responders to protein nutritional status. Interesting findings included the drastic changes in the levels of genes for Id (inhibitor of DNA binding) proteins, which are involved in the regulation of multiple genes, and of a set of genes in the pathway of cholesterol biosynthesis and disposal. This study represents a step toward a more global understanding of gene expression changes in states of protein malnutrition.

Animals↗
PubMed2002

Recent trends in functional food science and the industry in Japan.

International recognition of functional foods has resulted in the recent global development of this field, which originated in Japan. The national policy on functional foods, in terms of "foods for specified health use", also has been developing and has motivated the food industry to produce a variety of new food items. In Japan as well as in many other countries, academic and industrial scientists have been working in collaboration for the analysis and practical applications of functional food science. Emphasis has been placed on the study of antioxidant and anticarcinogenic food factors as well as pre- and probiotics. This review pinpoints recent trends in the science and industry in this field.

Animals↗
PubMed2002

Transepithelial transport of the bioactive tripeptide, Val-Pro-Pro, in human intestinal Caco-2 cell monolayers.

Some of the food-derived tripeptides with angiotensin converting enzyme (ACE)-inhibitory activity have been reported to be hypotensive after being orally administered. The mechanism for the intestinal transport of these tripeptides was studied by using monolayer-cultured human intestinal Caco-2 cells which express many enterocyte-like functions including the peptide transporter (PepT1)-mediated transport system. Val-Pro-Pro, an ACE-inhibitory peptide from fermented milk, was used as a model tripeptide. A significant amount of intact Val-Pro-Pro was transported across the Caco-2 cell monolayer. This transport was hardly inhibited by a competitive substrate for PepT1. Since no intact Val-Pro-Pro was detected in the cells, Val-Pro-Pro apically taken by Caco-2 cells via PepT1 was likely to have been quickly hydrolyzed by intracellular peptidases, producing free Val and Pro. These findings suggest that PepT1-mediated transport was not involved in the transepithelial transport of intact Val-Pro-Pro. Paracellular diffusion is suggested to have been the main mechanism for the transport of intact Val-Pro-Pro across the Caco-2 cell monolayer.

Biological Transport↗