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Biomedical subjects

Hideyuki Suzuki

Publications and source records attributed to Hideyuki Suzuki.

53 records · Page 3Linked to original sources
PubMed2004

An extracellular aspartic protease functions in Arabidopsis disease resistance signaling.

We have used activation tagging with T-DNA carrying cauliflower mosaic virus 35S enhancers to investigate the complex signaling networks underlying disease resistance in Arabidopsis. From a screen of approximately 5000 lines, we identified constitutive disease resistance (CDR1) encoding an apoplastic aspartic protease, the overexpression of which causes dwarfing and resistance to virulent Pseudomonas syringae. These phenotypes reflect salicylic-acid-dependent activation of micro-oxidative bursts and various defense-related genes. Antisense CDR1 plants were compromised for resistance to avirulent P. syringae and more susceptible to virulent strains than wild type. CDR1 accumulates in intercellular fluid in response to pathogen attacks. Induction of CDR1 generates a small mobile signal, and CDR1 action is blocked by the protease inhibitor pepstatin and by mutations in the protease active sites. We propose that CDR1 mediates a peptide signal system involved in the activation of inducible resistance mechanisms.

Amino Acid Sequence↗
PubMed2004

A single amino acid substitution converts gamma-glutamyltranspeptidase to a class IV cephalosporin acylase (glutaryl-7-aminocephalosporanic acid acylase).

The aspartyl residue at position 433 of gamma-glutamyltranspeptidase of Escherichia coli K-12 was replaced by an asparaginyl residue. This substitution enabled gamma-glutamyltranspeptidase to deacylate glutaryl-7-aminocephalosporanic acid, producing 7-aminocephalosporanic acid, which is a starting material for the synthesis of semisynthetic cephalosporins.

Amino Acid Substitution↗
PubMed2004

Identification of the LIV-I/LS system as the third phenylalanine transporter in Escherichia coli K-12.

In Escherichia coli, the active transport of phenylalanine is considered to be performed by two different systems, AroP and PheP. However, a low level of accumulation of phenylalanine was observed in an aromatic amino acid transporter-deficient E. coli strain (DeltaaroP DeltapheP Deltamtr Deltatna DeltatyrP). The uptake of phenylalanine by this strain was significantly inhibited in the presence of branched-chain amino acids. Genetic analysis and transport studies revealed that the LIV-I/LS system, which is a branched-chain amino acid transporter consisting of two periplasmic binding proteins, the LIV-binding protein (LIV-I system) and LS-binding protein (LS system), and membrane components, LivHMGF, is involved in phenylalanine accumulation in E. coli cells. The K(m) values for phenylalanine in the LIV-I and LS systems were determined to be 19 and 30 micro M, respectively. Competitive inhibition of phenylalanine uptake by isoleucine, leucine, and valine was observed for the LIV-I system and, surprisingly, also for the LS system, which has been assumed to be leucine specific on the basis of the results of binding studies with the purified LS-binding protein. We found that the LS system is capable of transporting isoleucine and valine with affinity comparable to that for leucine and that the LIV-I system is able to transport tyrosine with affinity lower than that seen with other substrates. The physiological importance of the LIV-I/LS system for phenylalanine accumulation was revealed in the growth of phenylalanine-auxotrophic E. coli strains under various conditions.

Amino Acid Transport Systems↗
PubMed2004

Gamma-glutamyltranspeptidase, but not YwrD, is important in utilization of extracellular glutathione as a sulfur source in Bacillus subtilis.

gamma-Glutamyltranspeptidase (EC 2.3.2.2) of Bacillus subtilis, which is an extracellular enzyme, hydrolyzes the gamma-glutamyl linkage of glutathione. YwrD, which is homologous to gamma-glutamyltranspeptidase, was speculated to have a similar physiological role. It was shown that gamma-glutamyltranspeptidase, but not YwrD, is important in utilizing glutathione as the sole sulfur source in Bacillus subtilis.

Bacillus subtilis↗
PubMed2003

Signals for local and systemic responses of plants to pathogen attack.

Activation of plant defences following recognition of pathogen attack involves complex reiterative signal networks with extensive signal amplification and cross-talk. The results of two approaches that have been taken to analyse signalling in plant-microbe interactions are discussed here. Activation tagging with T-DNA harbouring multiple 35S enhancer elements was employed as a gain-of-function approach to dissect signalling related to bacterial pathogen resistance in Arabidopsis thaliana. From a screen of approximately 5000 activation tagged lines, one line was identified as harbouring a T-DNA leading to over-expression of an apoplastic aspartic protease (CDR-1), that resulted in resistance to normally virulent Pseudomonas syringae. The second approach was to screen for loss-of-function mutants in T-DNA tagged populations. From a screen of 11 000 lines, one line, defective in induced resistance-1 (dir-1) lost resistance to normally avirulent P. syringae. Models for action of the products of the CDR-1 and DIR-1 genes suggest involvement of peptide and lipid signals in systemic disease resistance responses in A. thaliana.

Arabidopsis↗
PubMed2003

A mutant Bacillus subtilis gamma-glutamyltranspeptidase specialized in hydrolysis activity.

gamma-Glutamyltranspeptidase (GGT) catalyzes the hydrolysis of gamma-glutamyl compounds and the transfer of their gamma-glutamyl moieties to amino acids and peptides. The transpeptidation activity of Bacillus subtilis GGT is about 10-fold higher than its hydrolysis activity. In B. subtilis GGT, substitution of Asp-445 with Ala abolished its transpeptidation activity. The specific activity for hydrolysis of D445A GGT was 40.2% of that of the wild-type GGT. The K(m) value for L-glutamine was 15.3 mM. D445A GGT was salt tolerant like the wild-type GGT. These results indicate that D445A GGT will be highly useful as a 'glutaminase' in food industry.

Bacillus subtilis↗
PubMed2003

A yeast two-hybrid assay provides a simple way to evaluate the vast majority of hMLH1 germ-line mutations.

Germ-line mutations in the hMLH1 gene are the most frequent cause of hereditary nonpolyposis colorectal cancer and are characterized by missense mutations at high frequency. We found a yeast two-hybrid assay to be an extremely useful and simple tool for evaluating the biological significance of such hMLH1 germ-line missense mutations; 78% (18 of 23) of the missense ones can be recognized as causative for nonpolyposis colorectal cancer. In addition, two of five variants not recognized as causative were thought to be rare polymorphisms. However, we could not detect any differences between wild-type hMLH1 and any of the nine already known polymorphisms causing amino acid alterations. Additional analysis demonstrated that the two-hybrid assay not only detected the dysfunctions at the COOH terminus of the hMLH1 protein necessary for the interaction with associated proteins but also detected a conformational change at the NH(2) terminus carrying ATPase activity. Thus, this method provides a simple and reliable system for accurate diagnosis of hMLH1 alterations.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Use of bacterial gamma-glutamyltranspeptidase for enzymatic synthesis of gamma-D-glutamyl compounds.

An enzymatic method for synthesizing various gamma-D-glutamyl compounds efficiently and stereospecifically involving bacterial gamma-glutamyltranspeptidase (EC 2.3.2.2) with D-glutamine as a gamma-glutamyl donor was developed. With D-glutamine as a gamma-glutamyl donor instead of L-glutamine in gamma-glutamyltaurine synthesis, by-products such as gamma-glutamylglutamine and gamma-glutamyl-gamma-glutamyltaurine were not synthesized and the yield of gamma-glutamyltaurine dramatically increased from 25 to 71%. It was also shown that the purification could be simplified without these gamma-glutamyl by-products. The possibility of synthesizing various gamma-D-glutamyl compounds was also shown.

Biotechnology↗
PubMed2002

Autocatalytic processing of gamma-glutamyltranspeptidase.

gamma-Glutamyltranspeptidase is the key enzyme in glutathione metabolism, and we previously presented evidence suggesting that it belongs to the N-terminal nucleophile hydrolase superfamily. Enzymatically active gamma-glutamyltranspeptidase, which consists of one large subunit and one small subunit, is generated from an inactive common precursor through post-translational proteolytic processing. The processing mechanism for gamma-glutamyltranspeptidase of Escherichia coli K-12 has been analyzed by means of in vitro studies using purified precursors. Here we show that the processing of a precursor of gamma-glutamyltranspeptidase is an intramolecular autocatalytic event and that the catalytic nucleophile for the processing reaction is the oxygen atom of the side chain of Thr-391 (N-terminal residue of the small (beta) subunit), which is also the nucleophile for the enzymatic reaction.

Catalysis↗
PubMed2002

Array-enhanced coherence resonance and forced dynamics in coupled FitzHugh-Nagumo neurons with noise.

Nonlinear dynamics of coupled FitzHugh-Nagumo neurons subject to independent noise is analyzed. A kind of self-sustained global oscillation with almost synchronous firing is generated by array-enhanced coherence resonance. Further, forced dynamics of the self-sustained global oscillation stimulated by sinusoidal input is analyzed and classified as synchronized, quasiperiodic, and chaotic responses just like the forced oscillations in nerve membranes observed by in vitro experiments with squid giant axons. Possible physiological importance of such forced oscillations is also discussed.

Animals↗
PubMed2002

Improvement of the bitter taste of amino acids through the transpeptidation reaction of bacterial gamma-glutamyltranspeptidase.

The tastes of several bitter amino acids and their gamma-glutamyl derivatives were compared. The bitterness of Phe, Val, Leu, and His was reduced, sourness was produced, and preferences were increased by gamma-glutamylization. Because the effect of gamma-glutamylization of bitter amino acids was most obvious for Phe, which is an atypical bitter amino acid, an enzymatic method for the synthesis of gamma-glutamylphenylalanine (gamma-Glu-Phe) involving bacterial gamma-glutamyltranspeptidase was developed. The optimum reaction conditions were 200 mM Gln, 200 mM Phe, and 0.5 unit/mL GGT, pH 10.4. After 1.5-h of incubation at 37 degrees C, 140 mM gamma-Glu-Phe was obtained, the yield being 70%. gamma-Glu-Phe was purified on a Dowex 1x8 column and then identified by NMR.

Amino Acids↗
PubMed2002

Simple liver cyst with spontaneous regression.

We report a-55-year-old woman with spontaneous regression of simple liver cyst. The size of the cyst gradually became reduced without any treatment, and a reduction in diameter from 77 mm to 10 mm was observed after 8 years of follow-up. Spontaneous regression of congenital cysts of the liver in an adult seems to be very rare, and its mechanism is discussed.

Cysts↗
PubMed2002

A genomics approach to the early stages of triterpene saponin biosynthesis in Medicago truncatula.

The saponins of the model legume Medicago truncatula are glycosides of at least five different triterpene aglycones: soyasapogenol B, soyasapogenol E, medicagenic acid, hederagenin and bayogenin. These aglycones are most likely derived from beta-amyrin, a product of the cyclization of 2,3-oxidosqualene. Mining M. truncatula EST data sets led to the identification of sequences putatively encoding three early enzymes of triterpene aglycone formation: squalene synthase (SS), squalene epoxidase (SE), and beta-amyrin synthase (beta-AS). SS was functionally characterized by expression in Escherichia coli, two forms of SE by complementation of the yeast erg1 mutant, and beta-AS by expression in yeast. Beta-amyrin was the sole product of the cyclization of squalene epoxide by the recombinant M. truncatulabeta-AS, as judged by GC-MS and NMR. Transcripts encoding beta-AS, SS and one form of SE were strongly and co-ordinately induced, associated with accumulation of triterpenes, upon exposure of M. truncatula cell suspension cultures to methyl jasmonate. Sterol composition remained unaffected by jasmonate treatment. Molecular verification of induction of the triterpene pathway in a cell culture system provides a new tool for saponin pathway gene discovery by DNA array-based approaches.

Acetates↗
PubMed2002

Functional analysis of the Erwinia herbicola tutB gene and its product.

The tutB gene, which lies just downstream of tpl, has been cloned from Erwinia herbicola, and its product was analyzed. Despite its high sequence similarity to tryptophan transporters, TutB was found to be a tyrosine-specific transporter. Tryptophan acted as a competitive inhibitor of tyrosine transport. Unlike the tryptophanase operon, the tpl and tutB genes do not constitute an operon.

Amino Acid Sequence↗
PubMedDate not supplied

Intratumoral induction of thymidylate synthase mRNA by 5-FU in colorectal cancer patients: association with survival.

Dihydropyrimidine dehydrogenase (DPD) is the rate-limiting enzyme in 5-fluorouracil (5-FU) catabolism. Thymidylate synthase (TS) is inhibited to form an inactive ternary complex by 5-fluoro-dUMP and is considered to be a target enzyme of 5-FU treatment. Two enzymes, DPD and TS, have been reported to be major determinants of individual sensitivity to 5-FU, and it has been reported that TS mRNA levels are modified by 5-FU treatment. We investigated their impact on treatment efficacy in colorectal cancer patients. TS and DPD mRNA levels, which correlated to the corresponding enzyme activities, were quantified in tumor tissues before and after treatment in 40 advanced colorectal cancer patients who had been treated with Doxifluridine (5'-DFUR) for 14 days before surgery. Furthermore inter-individual variations of TS mRNA levels after 5-FU treatment were found, and the individual TS induction varied between patients (0.2-2.4). Increased TS mRNA levels were found in 19 out of 40 cases. The samples were divided into two groups according to their TS mRNA induction (< or >1; TS/beta-actin ratio after treatment divided by values prior treatment) and compared with tumor reduction and survival. TS and DPD mRNA levels in tumor biopsies before treatment were not related to 5-FU responses by histological evaluations in this study. However the efficacy of 5-FU treatment was enhanced in patients with no or low TS mRNA induction (odds ratio: 6.2, p<0.05). Furthermore, longer periods of survival were observed in the group without increased TS mRNA levels. These findings suggest that TS mRNA was induced by 5-FU treatment, and the overall induction level varied between individuals. Therefore, the estimation of TS mRNA induction may be useful to predict the efficacy of 5-FU treatment.

Aged↗
PubMedDate not supplied

Third-line chemotherapy with paclitaxel, irinotecan hydrochloride and cisplatin for recurrent gastric cancer: a case report.

With the availability of new chemotherapeutic agents such as S-1 and paclitaxel (TXL) for advanced gastric cancer, the development of a strategy for a third-line chemotherapy is urgently needed. We treated a patient with recurrent gastric cancer using TXL, irinotecan hydrochloride (CPT-11) and cisplatin (CDDP) as a third-line chemotherapy. The patient was a 46-year-old man who had undergone total gastrectomy for advanced gastric cancer with lymph node metastases. For postoperative recurrence, he was first treated with S-1 as an outpatient; however, tumor markers increased, and para-aortic lymph node metastasis was revealed by thoracic and abdominal CT scan. A second-line therapy with weekly TXL and CDDP was then added, but resulted in PD. Therefore, combination chemotherapy with TXL, CPT-11 and CDDP was started biweekly as a third-line chemotherapy. TXL (80mg/m2) was infused over 1 hour after short premedication, followed by CPT-11 (25mg/m2) and CDDP (15mg/m2) over 30 min. After 6 courses of this therapy, the serum AFP and TPA returned to normal, and the size of the metastatic para-aortic lymph nodes reduced. The effect of this therapy was judged as PR and the toxicity of this regimen was tolerable. The patient has undergone 10 courses of this therapy and is maintaining a clinical PR. The patient was able to resume his full social activities. TXL, CPT-11 and CDDP combination chemotherapy may be useful and safe for patients with recurrent gastric cancer, even after first-or second-line therapy with S-1 or taxanes.

Adenocarcinoma↗