Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rhodobacter capsulatus is a Gram-negative photosynthetic bacterium that requires c-type cytochromes for photosynthetic electron transport. Our studies demonstrate that the gene helX is required for the biogenesis of c-type cytochromes in R. capsulatus. A helX chromosomal deletion mutant cannot grow photosynthetically, due to a deficiency of all c-type cytochromes. The predicted amino acid sequence of the helX gene product (176 residues) is related to that of thioredoxin and shares active-site homology with protein disulfide isomerase. Cytochrome c2-alkaline phosphatase gene fusions are used to show that HelX is not required for the transcription, translation, or secretion of apocytochrome c2. HelX-alkaline phosphatase and HelX-beta-galactosidase gene fusions are used to demonstrate that HelX is a periplasmic protein, which is consistent with the presence of a typical signal sequence in HelX. Based on these results, we propose HelX functions as a periplasmic disulfide oxidoreductase that is essential for cytochromes c biogenesis. This role is in accordance with the observation that both heme and the cysteines of apocytochromes c (Cys-Xaa-Yaa-Cys-His) must be in the reduced state for covalent linkage between the two moieties to occur.
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PMID:Cytochromes c biogenesis in a photosynthetic bacterium requires a periplasmic thioredoxin-like protein. 838 15

The structural gene (trxA) coding for thioredoxin in the photosynthetic bacterium Rhodobacter sphaeroides has been cloned and sequenced previously. In the present study, the role of oxygen in trxA expression in R. sphaeroides Y was investigated using mRNA analyses and plasmid-borne trxA'-lacZ+ translational and transcriptional fusions. Northern analysis revealed a trxA-specific transcript of approximately 420-460 nucleotides, indicating that trxA is transcribed as a single gene. By studying the beta-galactosidase activity in strains harboring various phi(trxA'-lacZ+) fusion constructs, the promoter region of the trxA gene was localized within a 64-bp region located 97 nucleotides upstream of the trxA initiator codon. A single trxA transcription initiation site was mapped by primer extension, 27 bp upstream of the trxA gene. Based on these results and the DNA sequence analysis, we propose that a sigma70 consensus sequence serves as a trxA promoter. Results from oxygen shift experiments, as deduced from both mRNA analysis and fusions of the trxA promoter region to lacZ indicate that transcription of the R. sphaeroides trxA gene is regulated by high oxygen tension. DNA sequences involved in this oxygen regulation were also localized in the 64-bp region containing the trxA promoter. Based on our findings the hypothetical biological function of thioredoxin from R. sphaeroides is discussed.
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PMID:Expression of the thioredoxin gene (trxA) in Rhodobacter sphaeroides Y is regulated by oxygen. 862 18

Regulation of the Escherichia coli thioredoxin gene (trxA) was studied using trxA-lac translational fusion constructed in the vector pMC1403. Synthesis of beta-galactosidase from the trxA-lac fusion was found to be repressed in the presence of lactose. A switch of carbon source from glucose to lactose and an addition of cyclic AMP (cAMP) caused a decrease in beta-galactosidase synthesis from the trxA-lac fusion. The repression effect of exogenous cAMP was not observed in the crp mutant strain. The beta-galactosidase synthesis from the trxA-lac fusion lacking a plausible cAMP-CRP binding site was not lowered in the presence of lactose or in the addition of cAMP. Expression of the chromosomal trxA gene was reduced by exogenous cAMP. These findings indicate that the expression of the trxA gene is controlled by cAMP in a negative manner.
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PMID:Expression of the Escherichia coli thioredoxin gene is negatively regulated by cyclic AMP. 917 52

Hypoxia-inducible factor 1 alpha (HIF1alpha) and its related factor, HLF, activate expression of a group of genes such as erythropoietin in response to low oxygen. Transfection analysis using fusion genes of GAL4DBD with various fragments of the two factors delineated two transcription activation domains which are inducible in response to hypoxia and are localized in the C-terminal half. Their sequences are conserved between HLF and HIF1alpha. One is designated NAD (N-terminal activation domain), while the other is CAD (C-terminal activation domain). Immunoblot analysis revealed that NADs, which were rarely detectable at normoxia, became stabilized and accumulated at hypoxia, whereas CADs were constitutively expressed. In the mammalian two-hybrid system, CAD and NAD baits enhanced the luciferase expression from a reporter gene by co-transfection with CREB-binding protein (CBP) prey, whereas CAD, but not NAD, enhanced beta-galactosidase expression in yeast by CBP co-expression, suggesting that NAD and CAD interact with CBP/p300 by a different mechanism. Co-transfection experiments revealed that expression of Ref-1 and thioredoxin further enhanced the luciferase activity expressed by CAD, but not by NAD. Amino acid replacement in the sequences of CADs revealed a specific cysteine to be essential for their hypoxia-inducible interaction with CBP. Nuclear translocation of thioredoxin from cytoplasm was observed upon reducing O2 concentrations.
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PMID:Molecular mechanisms of transcription activation by HLF and HIF1alpha in response to hypoxia: their stabilization and redox signal-induced interaction with CBP/p300. 1020 54

A cDNA coding thioredoxin (TRX) was isolated from a cDNA library of Schizosaccharomyces pombe by colony hybridization. The 438 bp EcoRI fragment, which was detected by Southern hybridization, reveals an open reading frame which encodes a protein of 103 amino acids. The genomic DNA encoding TRX was also isolated from S. pombe chromosomal DNA using PCR. The cloned sequence contains 1795 bp and encodes a protein of 103 amino acids. However, the C-terminal region obtained from the cDNA clone is -Val-Arg-Leu-Asn-Arg-Ser-Leu, whereas the C-terminal region deduced from the genomic DNA appears to contain -Ala-Ser-Ile-Lys-Ala-Asn-Leu. This indicates that S. pombe cells contain two kinds of TRX genes which have dissimilar amino acid sequences only at the C-terminal regions. The heterologous TRX 1C produced from the cDNA clone could be used as a subunit of T7 DNA polymerase, while the TRX 1G from the genomic DNA could not. The upstream sequence and the region encoding the N-terminal 18 amino acids of the genomic DNA were fused into the promoterless beta-galactosidase gene of the shuttle vector YEp357 to generate the fusion plasmid pYKT24. Synthesis of beta-galactosidase from the fusion plasmid was found to be enhanced by hydrogen peroxide, menadione and aluminum chloride. It indicates that the expression of the cloned TRX gene is induced by oxidative stress.
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PMID:Characterization and regulation of Schizosaccharomyces pombe gene encoding thioredoxin. 1126 79

The genomic DNA encoding thioredoxin (TRX) was previously isolated from the fission yeast Schizosaccharomyces pombe. In this investigation, regulation of the S. pombe TRX gene was studied in lacZ translational fusions. The synthesis of beta-galactosidase from the fusion plasmid pYKT24 was significantly enhanced by treatments with cadmium chloride, zinc chloride, and high temperatures. Synthesis of beta-galactosidase from the fusion plasmid was significantly decreased by higher concentrations (5 microM, 10 microM) of mercuric chloride, whereas it was enhanced by its lower concentration (1 microM). Diamide affected the synthesis of beta-galactosidase in the same manner with mercuric chloride. However, high osmolarity had no effect on the beta-galactosidase synthesis from the fusion plasmid pYKT24. Various fusion plasmids were constructed to carry serially deleted upstream regions of the TRX gene. Pap1 mediates the regulation of the S. pombe TRX gene. The upstream region, between 987 and 1,270 bp from the translational initiation point, is responsible for the regulation.
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PMID:Pap1-mediated regulation of thioredoxin gene from Schizosaccharomyces pombe. 1201 55

A genomic DNA encoding a second thioredoxin (TRX2) was isolated from the chromosomal DNA of the fission yeast Schizosaccharomyces pombe. The cloned sequence contains 1823 bp and encodes a protein of 121 amino acids. It has extra N-terminal 17 amino acid residues compared to previously identified thioredoxin (TRX1), which are positively charged and hydrophobic amino acids. The additional N-terminal region contains a plausible prepeptidase cleavage site, indicating that the TRX2 protein exists in mitochondria. The cloned TRX2 gene produced functional TRX estimated with insulin reduction assay. The upstream region of the TRX2 gene was fused into the promoterless beta-galactosidase gene of the shuttle vector YEp357R. The 782 bp sequence in the region further upstream of the TRX2 gene was found to be inhibitory in its expression. Synthesis of beta-galactosidase from the fusion plasmid pYFX135-HRL was enhanced by the addition of aluminum chloride and ferrous chloride, indicating that the TRX2 protein is involved in stress response.
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PMID:Characterization and regulation of a second gene encoding thioredoxin from the fission yeast. 1202 Aug 31

The structural gene encoding a third thioredoxin (Trx) homologue, TRX3, of the fission yeast Schizosaccharomyces pombe was characterized and its regulation was studied. The determined DNA sequence encoded a putative 290 amino acid sequence of Trx with a molecular mass of 31,889 Da. The TRX3 mRNA level was increased in S. pombe cells harboring plasmid pTRX3, suggesting that the cloned TRX3 gene was functional. Yeast cultures harbouring plasmid pTRX3 exhibited shorter generation times and higher survival on solid minimal media plates incorporating mercury chloride (0.01 mmol/L) or hydrogen peroxide (1 mmol/L) compared with control cultures. Yeast cells containing extra copies of TRX3, but not TRX1 and TRX2, gave rise to lower reactive oxygen species levels than control cells. Oxidative stress owing to hydrogen peroxide and menadione enhanced the synthesis of beta-galactosidase from the TRX3-lacZ fusion gene in Pap1-positive cells but not in Pap1-negative cells. The TRX3 mRNA level was increased by oxidative stress only in Pap1-positive cells. Basal expression of the TRX3 gene also depended on Pap1. We concluded that S. pombe TRX3 is linked with yeast growth and oxidative stress response, with its expression being regulated by oxidative stress in a Pap1-dependent manner.
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PMID:Cellular functions and transcriptional regulation of a third thioredoxin from Schizosaccharomyces pombe. 1766 38

The only family 1 glycoside hydrolase in Clostridium cellulolyticum H10 (CcGH1) is annotated as a beta-galactosidase but has high sequence homology with many beta-glucosidases. Given the possible importance of beta-glucosidase in cellulose utilization by C. cellulolyticum, the encoding open reading frame Ccel_0374 was cloned and expressed in E. coli as a soluble fusion protein with thioredoxin. After tag cleavage, the purified enzyme had a molecular mass of 52 kDa and was active in dimeric form on a broad range of substrates, including cellobiose, cellotriose, cellotetraose, p-nitrophenyl-beta-glucopyranoside, lactose, and o-nitrophenyl-beta-galactopyranoside. The enzyme showed lower K(m) and higher catalytic efficiency (k (cat)/K(m)) on cellodextrins with degree of polymerization from 2 to 4 than on lactose, and the k (cat)/K (m) values on cellodextrins increased in the order of cellobiose < cellotriose < cellotetraose, suggesting that CcGH1 was a cellodextrin glucohydrolase (EC 3.2.1.74). The high K(m) (69 mM) on cellobiose implies that CcGH1 likely has a minimal role in the intracellular hydrolysis of cellobiose in C. cellulolyticum. The three-dimensional structure model of CcGH1 generated by homology modeling showed a typical (alpha/beta)(8) barrel topology characteristic of family 1 glycoside hydrolases.
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PMID:The family 1 glycoside hydrolase from Clostridium cellulolyticum H10 is a cellodextrin glucohydrolase. 1981 61