Innovation in the food industry using microbial transglutaminase: Keys to success and future prospects.

Transglutaminase (TG) catalyzes cross-linking between the γ-carboxyamide groups of glutamine residues and the ε-amino groups of lysine residues in polypeptide chains, yielding ε- (γ-glutamyl) lysine (G-L) bonds. By forming a network structure in the protein via G-L bonds, it is possible to increase the viscosity of protein solutions or to cause gelation. Nearly thirty years have passed since microbial TG (MTG) appeared in the food enzyme market. Since the start of research and development, MTG has been used in fishery products such as kamaboko (boiled fish paste), meat products such as sausages, milk products such as yogurt, processed-soybean products such as tofu, and wheat products such as bread and noodles. MTG has provided effects such as adding new functions and reducing waste in food applications. The purpose of this review is to describe not only the history of research and development of TG but also the key aspects that have facilitated the great success of this process as a technology for enzymatically modifying protein-containing foods.

Screening of microorganisms producing a novel protein-asparaginase and characterization of the enzyme derived from Luteimicrobium album.

A screening system using enrichment culture has been established with the aim of obtaining a novel enzyme for protein modification that has not been previously reported. This enzyme catalyzes deamidation of the side-chain amide group of asparagine in proteins. Enrichment culture of 390 soil samples was carried out with Z-Asn-Gly as the sole source of nitrogen, and the reaction product, Z-Asp-Gly, was detected in the culture supernatant of 102 strains. Strains with particularly high activity were Leifsonia sp., Luteimicrobium sp., Microbacterium sp., and Agromyces sp., all belonging to the class Actinobacteria. Of these, a protein-asparaginase (PA) was obtained from the culture supernatant of Luteimicrobium album 333B-h1, and its reactivity with different substrates and its basic enzymatic characteristics were investigated. Addition of the enzyme solution resulted in specific deamidation of only the asparagine residue in insulin chain B. The enzyme showed no reactivity with free asparagine or asparagine in low molecular weight peptides. It was demonstrated that the enzyme reacts with various protein substrates. In particular, proteins that have open structures, such as casein or gelatin, were good substrates. The activity and stability of PA at different temperatures and pH values were investigated. It was found that a temperature of 37°C and a roughly neutral pH are optimal conditions for the enzyme.

The ß-catenin signaling pathway induces aggressive potential in breast cancer by up-regulating the chemokine CCL5.

ß-Catenin signaling plays a pivotal role in the genesis of a variety of malignant tumors, but its role in breast cancer has not been fully elucidated. Here, we examined whether deregulation of ß-catenin signaling is related to the aggressive characteristics of certain types of breast cancers. Analysis of cytokine levels in MDA-MB-231 cells overexpressing a constitutively active form of ß-catenin (CAß-catenin) revealed a higher level of CCL5 expression. Cells transfected with CAß-catenin or stimulated with recombinant CCL5 exhibited increased cell invasion activity and spheroid formation in vitro. Furthermore, CAß-catenin-transfected MDA-MB-231 cells formed larger tumor masses that contained more Ki-67-positive cells and infiltrating lymphocytes than did the control cells. An inhibitor of CCR5 and a pan-CXCR neutralizing antibody dramatically reduced CAß-catenin-promoted activities. In addition to CCL5, 6-BIO, a chemical activator of ß-catenin, induced cell invasion and spheroid formation in MDA-MB-231 cells. Furthermore, high levels of nuclear ß-catenin accumulation were detected in breast cancer in patients with metastasis but not in those without metastasis. Nuclear ß-catenin localization is related to increased CCL5 production in breast cancer. These findings suggest that ß-catenin expression enhances tumor progression via chemokine production in breast cancers and that ß-catenin signaling is a critical regulator of the aggressive traits of breast cancers.

Increased oxidative stress in AOA3 cells disturbs ATM-dependent DNA damage responses.

Ataxia telangiectasia (AT) is caused by a mutation in the ataxia-telangiectasia-mutated (ATM) gene; the condition is associated with hyper-radiosensitivity, abnormal cell-cycle checkpoints, and genomic instability. AT patients also show cerebellar ataxia, possibly due to reactive oxygen species (ROS) sensitivity in neural cells. The ATM protein is a key regulator of the DNA damage response. Recently, several AT-like disorders have been reported. The genes responsible for them are predicted to encode proteins that interact with ATM in the DNA-damage response. Ataxia with oculomotor apraxia types 1-3 (AOA1, 2, and 3) result in a neurodegenerative and cellular phenotype similar to AT; however, the basis of this phenotypic similarity is unclear. Here, we show that the cells of AOA3 patients display aberrant ATM-dependent phosphorylation and apoptosis following γ-irradiation. The ATM-dependent response to H2O2 treatment was abrogated in AOA3 cells. Furthermore, AOA3 cells had reduced ATM activity. Our results suggest that the attenuated ATM-related response is caused by an increase in endogenous ROS in AOA3 cells. Pretreatment of cells with pyocyanin, which induces endogenous ROS production, abolished the ATM-dependent response. Moreover, AOA3 cells had decreased homologous recombination (HR) activity, and pyocyanin pretreatment reduced HR activity in HeLa cells. These results indicate that excess endogenous ROS represses the ATM-dependent cellular response and HR repair in AOA3 cells. Since the ATM-dependent cell-cycle checkpoint is an important block to carcinogenesis, such inactivation of ATM may lead to tumorigenesis as well as neurodegeneration.

Effect of enzymatic deamidation on the heat-induced conformational changes in whey protein isolate and its relation to gel properties.

The effect of protein-glutaminase (PG) on the heat-induced conformational changes in whey protein isolate (WPI) and its relation to gel properties was investigated. The structural properties of WPI treated with PG were examined by several analytical methods. The analysis of the fluorescence spectrum and the binding capacity of a fluorescent probe demonstrated that deamidation prevented the increase in the fluorescence intensity caused by subsequent heat treatment. Measurements of the molecular weight distribution of WPI showed that PG-treated WPI was not likely to polymerize even after heating. This is thought to be due to an increase in electrostatic repulsion between carboxylic acid groups and a decrease in the formation of disulfide bonds, which results in the decrease in heat-induced aggregation. The properties of heat-induced WPI gels were modified by deamidation. PG-treated WPI gels had a soft texture and a high water-holding capacity in the presence of salts.

Incorporation of 15N-labeled ammonia into glutamine amide groups by protein-glutaminase and analysis of the reactivity for α-lactalbumin.

Protein-glutaminase (PG) is an enzyme that catalyzes the deamidation of protein-bound glutamine residues. We found that an enzyme labeling technique (ELT), which is a stable isotope labeling method based on transglutaminase (TGase) reaction, is applicable for PG. PG catalyzed incorporation of (15)N-labeled ammonium ions into reactive glutamine amide groups in α-lactalbumin similarly to TGase and deamidated the most reactive glutamine amide group once labeled with (15)N. Furthermore, we investigated the effect of ammonium ions on the PG activity by peptide mapping, and more reactive glutamine residues were detected than were detected by the ELT in the presence of ammonium ions. This is probably because ammonium ions are competitive inhibitors, causing decreased reactivity for glutamine residues. We propose the reaction scheme of PG in the presence of the (15)N-labeled ammonium ions and show that the ELT method with PG is useful for evaluating the activity of PG.

Kinetic modeling and sensitivity analysis of xylose metabolism in Lactococcus lactis IO-1.

We proposed a kinetic simulation model of xylose metabolism in Lactococcus lactis IO-1 that describes the dynamic behavior of metabolites using the simulator WinBEST-KIT. This model was developed by comparing the experimental time-course data of metabolites in batch cultures grown in media with initial xylose concentrations of 20.3-57.8 g/l with corresponding calculated data. By introducing the terms of substrate activation, substrate inhibition, and product inhibition, the revised model showed a squared correlation coefficient (r2) of 0.929 between the experimental time-course of metabolites and the calculated data. Thus, the revised model is assumed to be one of the best candidates for kinetic simulation describing the dynamic behavior of metabolites. Sensitivity analysis revealed that pyruvate flux distribution is important for higher lactate production. To confirm the validity of our kinetic model, the results of the sensitivity analysis were compared with enzyme activities observed during increasing lactate production by adding natural rubber serum powder to the xylose medium. The experimental results on pyruvate flux distribution were consistent with the prediction by sensitivity analysis.

CtBP1/BARS is an activator of phospholipase D1 necessary for agonist-induced macropinocytosis.

Vesicular trafficking such as macropinocytosis is a dynamic process that requires coordinated interactions between specialized proteins and lipids. A recent report suggests the involvement of CtBP1/BARS in epidermal growth factor (EGF)-induced macropinocytosis. Detailed mechanisms as to how lipid remodelling is regulated during macropinocytosis are still undefined. Here, we show that CtBP1/BARS is a physiological activator of PLD1 required in agonist-induced macropinocytosis. EGF-induced macropinocytosis was specifically blocked by 1-butanol but not by 2-butanol. In addition, stimulation of cells by serum or EGF resulted in the association of CtBP1/BARS with PLD1. Finally, CtBP1/BARS activated PLD1 in a synergistic manner with other PLD activators, including ADP-ribosylation factors as demonstrated by in vitro and intact cell systems. The present results shed light on the molecular basis of how the 'fission protein' CtBP1/BARS controls vesicular trafficking events including macropinocytosis.

[The effects of various factors on cerebrovascular disease mortality rates in the 20th century and future trends in Japan].

PURPOSES: To analyze the outcomes of measures designed to decrease cerebrovascular diseases (CVDs) in Japan and to project CVD mortality trends into the 21st century based on an analysis of rates observed in the 20th century. METHODS: The numbers of CVD deaths and population sizes from 1920 to 2003 (excluding 1940 to 1946) by sex, year, and 5-year age group (from 20 to 79 years old) were used and effects of various factors on CVD mortality rates were estimated using Nakamura's Bayesian age-period-cohort model. The numbers of CVD deaths up to the year 2050 were projected based on estimates of age, cohort, and future period effects under three scenarios: (i) values remaining constant after year 2003; (ii) linearly extrapolated values; and (iii) quadratically extrapolated values, we obtained using a regression line for period effects from 1995 to 2003. RESULTS: The age, cohort, and period effects on CVD mortality rates were large and in order of the magnitude of their ranges. There were small differences between males and females. The age effect increased with aging and the period effect started decreasing after 1970. The cohort effect was high for birth cohorts born from the 1840s to the 1890s and low for those born from the 1920s to the 1970s. There were some differences in the cohort effect between males and females for birth cohorts born after 1940s; for females there was a gradual decrease, while for males there was a slight increase, after which it remained almost constant. According to the three scenarios, CVD deaths: (i) had upward trends through the projected period and peaked at around 2025 and 2045; (ii) remained almost constant at the present level for males, and decreased slightly for females; (iii) decreased for both males and females. CONCLUSIONS: The outcomes of measures designed to decrease CVDs were observed as period effects after 1970. Exposure to these measures is associated with prevention of CVD deaths. Nevertheless, in the first half of the 21st century, the number of CVD deaths is projected to increase due to the aging of the baby boomers and upward trends in the cohort effect for males. It would be necessary to adopt and develop both population strategies to decrease future period effects and high-risk strategies to decrease cohort effects for younger males who are currently in their twenties and thirties.

Involvement of N-terminal-extended form of sphingosine kinase 2 in serum-dependent regulation of cell proliferation and apoptosis.

Sphingosine kinase (SPHK) 1 is implicated in the regulation of cell proliferation and anti-apoptotic processes by catalyzing the formation of an important bioactive messenger, sphingosine 1-phosphate. Unlike the proliferative action of SPHK1, another isozyme, SPHK2, has been shown to possess anti-proliferative or pro-apoptotic action. Molecular mechanisms of SPHK2 action, however, are largely unknown. The present studies were undertaken to characterize the N-terminal-extended form of SPHK2 (SPHK2-L) by comparing it with the originally reported form, SPHK2-S. Real-time quantitative PCR analysis revealed that SPHK2-L mRNA is the major form in several human cell lines and tissues. From sequence analyses it was concluded that SPHK2-L is a species-specific isoform that is expressed in human but not in mouse. At the protein level it has been demonstrated by immunoprecipitation studies that SPHK2-L is the major isoform in human hepatoma HepG2 cells. SPHK2-L, when expressed in human embryonic kidney (HEK) 293 cells, did not show any inhibition of DNA synthesis in the presence of serum, whereas it showed marked inhibition in the absence of serum. Moreover, serum deprivation resulted in the translocation of SPHK2-L into the nuclei. In addition, serum deprivation induced SPHK2-L expression in HEK293 cells. Furthermore, suppression of SPHK2 by small interfering RNA treatment prevented serum deprivation- or drug-induced apoptosis in HEK293 cells. Taken together, these results indicate that a major form of SPHK2 splice variant, SPHK2-L, in human cells does not inhibit DNA synthesis under normal conditions and that SPHK2-L accumulation in the nucleus induced by serum deprivation may be involved in the cessation of cell proliferation or apoptosis depending on the cell type.

Delta-catenin/NPRAP (neural plakophilin-related armadillo repeat protein) interacts with and activates sphingosine kinase 1.

Sphingosine kinase (SPHK) is a key enzyme catalysing the formation of sphingosine 1-phosphate (SPP), a lipid messenger that is implicated in the regulation of a wide variety of important cellular events acting through intracellular, as well as extracellular, mechanisms. However, the molecular mechanism of intracellular actions of SPP remains unclear. Here, we have identified delta-catenin/NPRAP (neural plakophilin-related armadillo repeat protein) as a potential binding partner for SPHK1 by yeast two-hybrid screening. From co-immunoprecipitation analyses, the C-terminal portion of delta-catenin/NPRAP containing the seventh to tenth armadillo repeats was found to be required for interaction with SPHK1. Endogenous delta-catenin/NPRAP was co-localized with endogenous SPHK1 and transfected delta-catenin/NPRAP was co-localized with transfected SPHK1 in dissociated rat hippocampal neurons. MDCK (Madin-Darby canine kidney) cells stably expressing delta-catenin/NPRAP contained elevated levels of intracellular SPP. In a purified system delta-catenin/NPRAP stimulated SPHK1 in a dose-dependent manner. Furthermore, delta-catenin/NPRAP-induced increased cell motility in MDCK cells was completely inhibited by dimethylsphingosine, a specific inhibitor of SPHK1. These results strongly suggest that at least some of delta-catenin/NPRAP functions, including increased cell motility, are mediated by an SPHK-SPP signalling pathway.