Search PubMed⌕ Search

Biomedical subjects

Tomohiro Tamura

Publications and source records attributed to Tomohiro Tamura.

29 records · Page 2Linked to original sources
PubMed2004

Downregulation of the skeletal muscle pyruvate dehydrogenase complex in the Otsuka Long-Evans Tokushima Fatty rat both before and after the onset of diabetes mellitus.

The pyruvate dehydrogenase complex (PDC) catalyzes the irreversible oxidative decarboxylation of pyruvate in mitochondria. The PDC activity is regulated by a phosphorylation/dephosphorylation cycle catalyzed by specific kinases (PDK) and phosphatases (PDP). In this study, the regulatory mechanisms of PDC were examined in skeletal muscle of the spontaneously diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rat before and after the onset of diabetes. The Long-Evans Tokushima Otsuka (LETO) rat was used as control. Plasma glucose and insulin concentrations were at normal levels in both groups at 8 weeks of age but were significantly higher in OLETF than in LETO rats at 25 weeks of age (1.2-fold for glucose and 15-fold for insulin), indicating development of diabetes in the former. Plasma free fatty acids were 1.6-fold concentrated and the skeletal muscle PDC activity state was significantly lower in OLETF than in LETO rats at both ages, suggesting suppression of pyruvate oxidation in OLETF rats even before the onset of diabetes. The PDK activity and the abundance of the PDK isoform 4 protein as well as mRNA were greater in OLETF rats at both ages. Conversely, the abundance of the PDP isoform 1 protein and mRNA was less in OLETF than in LETO rats at both ages. These results suggest that concomitant greater PDK4 and less PDP1 expression in skeletal muscle of OLETF rats before the onset of diabetes are responsible for the lowering of the PDC activity and may be related with the development of diabetes mellitus.

Age Factors↗
PubMed2004

Isolation and characterization of the Rhodococcus opacus thiostrepton-inducible genes tipAL and tipAS: application for recombinant protein expression in Rhodococcus.

We cloned the Rhodococcus opacus (strain DSM 44193) tipA gene, which encodes two translation products, TipAL and TipAS. The gene products are homologous to the Streptomyces spp. TipAL and TipAS proteins, respectively. The tipA promoter is highly active and TipAS protein is predominantly accumulated in R. opacus cells when the inducer of transcription, thiostrepton, was presented in culture medium. We found that thiostrepton is also induced the expression of an endogenous TipA-family protein in Rhodococcus erythropolis (strain JCM3201). The minimal tipA promoter region was defined (57 bp) and the conserved nucleotide sequence of the putative TipAL protein binding site (TipA-box) was identified in that region. The tipA gene is presumed to be transcribed into a leaderless mRNA. We applied the tipA promoter successfully for recombinant protein expression in R. erythropolis cells.

Artificial Gene Fusion↗
PubMed2004

Venomous protease of aphid soldier for colony defense.

In social aphids, morphological, behavioral, and physiological differences between soldiers and normal insects are attributed to differences in gene expression between them, because they are clonal offspring parthenogenetically produced by the same mothers. By using cDNA subtraction, we identified a soldier-specific cysteine protease of the family cathepsin B in a social aphid, Tuberaphis styraci, with a second-instar soldier caste. The cathepsin B gene was specifically expressed in soldiers and first-instar nymphs destined to be soldiers. The cathepsin B protein was preferentially produced in soldiers and showed a protease activity typical of cathepsin B. The cathepsin B mRNA and protein were localized in the midgut of soldiers. For colony defense, soldiers attack enemies with their stylet, which causes paralysis and death of the victims. Notably, after soldiers attacked moth larvae, the cathepsin B protein was detected from the paralyzed larvae. Injection of purified recombinant cathepsin B protein certainly killed the recipient moth larvae. From these results, we concluded that the cathepsin B protein is a major component of the aphid venom produced by soldiers of T. styraci. Soldier-specific expression of the cathepsin B gene was found in other social aphids of the genus Tuberaphis. The soldier-specific cathepsin B gene showed an accelerated molecular evolution probably caused by the action of positive selection, which had been also known from venomous proteins of other animals.

Animals↗
PubMed2004

Cell-free protein synthesis using cell extract of Pseudomonas fluorescens and CspA promoter.

We have modified the cell-free coupled transcription/translation system of bacteria. The cell-free extract of Pseudomonas fluorescens was used for translation instead of Escherichia coli. In addition, transcription of the target gene was regulated by CspA promoter with endogenous RNA polymerase instead of by T7 promoter with exogenous T7 RNA polymerase. We could increase the yields of soluble proteins using different combinations of the S30 extract and the promoter and different temperatures for protein synthesis. Increasing the variety of synthesis systems allows production of large quantities of soluble proteins. In order to carry out efficient cell-free protein synthesis, versatile pCop-plasmids carrying CspA promoter were constructed and these plasmids were applicable to expression of recombinant proteins in E. coli cells.

Amino Acid Sequence↗
PubMed2004

Recombinant ATPases of the yeast 26S proteasome activate protein degradation by the 20S proteasome.

The 26S proteasome contains a proteolytic core, 20S proteasome, and its regulatory particle, 19S complex. That regulatory particle contains six ATPases that are involved in unfolding and translocation of substrates to the 20S proteasome's catalytic chamber. We expressed ATPase-encoding genes of the regulatory particle of Saccharomyces cerevisiae and found that some recombinant ATPases can self-assemble into a high-molecular-weight protein complex in Escherichia coli. Purification of the Rpt1Rpt2 hetero-complex and the Rpt4 homo-complex for functional characterization demonstrated their contribution to energy-dependent protein degradation. Our finding, production of a functional subunit of the 19S regulatory particle in bacteria, is a simpler and technically advanced system to functionally characterize individual subunits.

Adenosine Triphosphatases↗
PubMed2004

A novel system for expressing recombinant proteins over a wide temperature range from 4 to 35 degrees C.

Escherichia coli cells are the most commonly used host cells for large-scale production of recombinant proteins, but some proteins are difficult to express in E. coli. Therefore, we tested the nocardioform actinomycete Rhodococcus erythropolis, which grows at temperatures ranging from 4 to 35 degrees C, as an expression host cell. We constructed inducible expression vectors, where the expression of the target genes could be controlled with the antibiotic thiostrepton. Using these expression vectors, several milligrams of reporter proteins could be isolated from 1 liter of culture of R. erythropolis cells grown at a temperature range from 4 to 35 degrees C. Moreover, we successfully purified serum amyloid A1, NADH dehydorogenase 1 alpha subcomplex 4, cytochrome b5-like protein, apolipoprotein A-V, cathepsin D, pancreatic Rnase, and HMG-1 that are all difficult to express in E. coli. In the case of kallikrein 6, mouse deoxyribonuclease I and Kid1, which are also difficult to express in E. coli, the expression level of each protein increased when proteins were expressed at low temperature (4 degrees C). Based on these results, we conclude that a recombinant protein expression system using R. erythropolis as the host cell is superior to respective E. coli systems.

Aminopeptidases↗
PubMed2004

Isolation and characterization of a rolling-circle-type plasmid from Rhodococcus erythropolis and application of the plasmid to multiple-recombinant-protein expression.

We isolated, sequenced, and characterized the cryptic plasmid pRE8424 from Rhodococcus erythropolis DSM8424. Plasmid pRE8424 is a 5,987-bp circular plasmid; it carries six open reading frames and also contains cis-acting elements, specifically a single-stranded origin and a double-stranded origin, which are characteristic of rolling-circle-replication plasmids. Experiments with pRE8424 derivatives carrying a mutated single-stranded origin sequence showed that single-stranded DNA intermediates accumulated in the cells because of inefficient conversion from single-stranded DNA to double-stranded DNA. This result indicates that pRE8424 belongs to the pIJ101/pJV1 family of rolling-circle-replication plasmids. Expression vectors that are functional in several Rhodococcus species were constructed by use of the replication origin from pRE8424. We previously reported a cryptic plasmid, pRE2895, from R. erythropolis, which may replicate by a theta-type mechanism, like ColE2 plasmids. The new expression vectors originating from pRE8424 were compatible with those derived from pRE2895. Coexpression experiments with these compatible expression vectors indicated that the plasmids are suitable for the simultaneous expression of multiple recombinant proteins.

Amino Acid Sequence↗
PubMed2004

Analysis of bacterial glucose dehydrogenase homologs from thermoacidophilic archaeon Thermoplasma acidophilum: finding and characterization of aldohexose dehydrogenase.

The NADP(+)-preferring glucose dehydrogenase from thermoacidophilic archaeon Thermoplasma acidophilum has been characterized, and its crystal structure has been determined (Structure, 2:385-393, 1994). Its sequence and structure are not homologous to bacterial NAD(P)(+)-dependent glucose dehydrogenases, and its molecular weight is also quite defferent. On the other hand, three functionally unknown genes with homologies to bacterial NAD(P)(+)-dependent glucose dehydrogenases have been sequenced as part of the T. acidophilum genome project (gene names: Ta0191, Ta0747, and Ta0754 respectively). We expressed two genes of three, Ta0191 and Ta0754, in Escherichia coli, and purified the gene products to homogeneity. Dehydrogenase activities were thereby detected from the purified proteins. The Ta0754 gene product exhibited aldohexose dehydrogenase activity, and the Ta0191 gene product exhibited weak 2-deoxyglucose dehydrogenase activity. No aldohexose dehydrogenase gene has been isolated, while the enzyme was reported in 1968. This is the first report of the gene and primary structure. The purified Ta0754 gene product, designated AldT, was characterized. The enzyme AldT effectively catalyzed the oxidation of various aldohexoses, especially D-mannose. Lower activities on D-2-deoxyglucose, D-xylose, D-glucose, and D-fucose were detected although no activities were shown on other aldohexoses or additional sugars. As a cofactor, NAD(+) was much more suitable for the activity than NADP(+). The NAD(+)-preferring dehydrogenase most effectively reacting to D-mannose is for the first time. AldT was most active at pH 10 and above 70 degrees C, and completely stable up to 60 degrees C after incubation for 15 min. Other enzymatic properties were also investigated.

Bacterial Proteins↗
PubMed2003

Characterization of a novel intracellular endopeptidase of the alpha/beta hydrolase family from Streptomyces coelicolor A3(2).

In a proteasome-lacking mutant of Streptomyces coelicolor A3(2), an intracellular enzyme with chymotrypsin-like activity, absent from the wild type, was detected. Complementation that restored proteasome function did not suppress expression of the endopeptidase. Since the enzyme was not found in two other S. coelicolor proteasome mutants, its expression probably resulted from a secondary mutation arisen in the proteasome mutant. Purification of the endopeptidase revealed its identity to SCO7095, a putative hydrolase encoded by the S. coelicolor A3(2) genome with no known homologue. Based on the prediction of a Ser-Asp-His catalytic triad and an alpha/beta hydrolase fold, SCO7095 was assigned to peptidase clan SC. N-terminally His-tagged SCO7095 was efficiently expressed in Escherichia coli cells and purified for further characterization. Although SCO7095 is distantly related to several proline iminopeptidases, including Thermoplasma acidophilum tricorn-interacting F1, no aminopeptidase activity was detected. On synthetic substrates, the monomeric enzyme exhibited not only chymotrypsin-like activity but also thrombin-like activity.

Amino Acid Sequence↗