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Biomedical subjects

L F Wu

Publications and source records attributed to L F Wu.

At least 55 records · Page 3Linked to original sources
PubMed1990

Structure and evolution of a multidomain multiphosphoryl transfer protein. Nucleotide sequence of the fruB(HI) gene in Rhodobacter capsulatus and comparisons with homologous genes from other organisms.

The gene order of the fructose (fru) operon and nucleotide sequence of the first gene (fruB(HI) of Rhodobacter capsulatus are reported, analyzed and compared with homologous genes from other bacteria, and the gene products are identified. Included within the region reported is a gene encoding a multiphosphoryl transfer protein (MTP) of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). MTP consists of three moieties: a fructose-specific enzyme III (IIIfru)-like N-terminal moiety (residues 1 to 143) followed by an FPr(HPr)-like moiety (residues 157 to 245) and an enzyme I-like moiety (residues 273 to 827). The enzyme III-like moiety closely resembles the N-terminal 143 residues of the IIIfru-FPR fusion protein from Salmonella typhimurium (40.6% identity throughout its length) and the C-terminal 145 residues of the mannitol-specific enzyme II (IImtl) (37.8% identity throughout its length with the IIImtl moiety of IImtl). The FPr-like domain of MTP resembles the S. typhimurium FPr (42.4% identity) and the Escherichia coli or S. typhimurium HPr (38.8% identity). The enzyme I-like moiety resembles the E. coli enzyme I (38.9% identity). Predicted phosphorylation sites within the three functional units of MTP (His62 in the IIIfru-like moiety; His171 in the FPr-like moiety and His457 in the enzyme I-like moiety) were identified on the basis of sequence comparisons with the homologous proteins from enteric bacteria. The three functional domains of MTP are joined by two flexible "linkage" regions, rich in alanine, glycine and proline, which show 47% sequence identity with each other. They also exhibit a high degree of sequence identity with the linkage region of the mannose-specific enzyme III (IIIman) of the E. coli PTS as well as several other proteins of bacterial, eukaryotic and viral origin. At the RNA level, these linker regions formed hairpin structures with high (90%) G + C content. Analyses of the IIIfru-FPr fusion protein of S. typhimurium revealed that between the IIIfru and FPr moieties of this protein is a stretch of 142 amino acids that do not show homology to known PTS proteins. This region and the adjacent FPr-like region contain a sequence of 110 residues exhibiting 59% similarity to the receiver consensus motif defined by Kofoid and Parkinson. Because the Salmonella IIIfru-FPr fusion protein has been implicated in transcriptional regulation, this region of the Salmonella protein may prove to have regulatory significance.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1990

Regulation of bacterial physiological processes by three types of protein phosphorylating systems.

A single type of protein-phosphorylating system, the ATP-dependent protein kinases, is employed in the regulation of a variety of cellular physiological processes in eukaryotes. By contrast, recent work with bacteria has revealed that three types of protein-phosphorylating systems are involved in regulation: (1) the classical protein kinases, (2) the newly discovered sensor-kinase/response-regulator systems, and (3) the multifaceted phosphoenolpyruvate-dependent phosphotransferase system. Physiological and mechanistic aspects of these three evolutionarily distinct systems are discussed.

Bacteria↗
PubMed1990

Risk factor analysis of an epidemic of hepatitis A in a factory in Shanghai.

Investigation of an epidemic of hepatitis A which occurred in Shanghai in early 1988 was conducted at the Shanghai No. 2 Yarn Dyeing and Weaving Mill. In this factory the attack rate between January and April 1988 was 9%. The rate was highest among staff who ate raw clams (18%) and higher among those who ate cooked clams (7%) than among those who did not eat clams (2%). In addition, independent risk factors for infection were: age below 30 years (relative risk (RR) = 3.0, 95% Cl: 2.0, 4.5) shift work (RR = 3.3, 95% Cl: 1.9, 5.8) and eating out (RR = 4.7, 95% Cl: 2.3, 9.7). Consumption of clams contaminated with hepatitis A was the main risk factor in this episode. The study indicates that strengthening surveillance of shellfish hygiene is important in preventing future epidemics of hepatitis A.

Adult↗
PubMed1990

On the evolutionary origins of the bacterial phosphoenolpyruvate:sugar phosphotransferase system.

The genes encoding the proteins of the fructose-specific phosphotransferase system (PTS) of Rhodobacter capsulatus were sequenced, and the deduced amino acyl sequences of the energy-coupling protein, Enzyme I, and the transport protein, Enzyme IIfru, were compared with published sequences. Enzyme I was found to be homologous to pyruvate:phosphate dikinase of plants, while Enzyme IIfru was found to be homologous to the insulin-responsive glucose facilitator of mammals. The evolutionary and functional implications of these findings are discussed.

Amino Acid Sequence↗
PubMed1990

Corrected sequence of the mannitol (mtl) operon in Escherichia coli.

The previously published sequences of the operator-promoter region of the mannitol operon of Escherichia coli and of the mtlD gene have been found to contain a number of errors. The major conclusions reported previously were correct, but additionally it is now clear that a C-terminal portion of mannitol-1-phosphate dehydrogenase (the mtlD gene product) exhibits significant sequence identity with an amino-terminal region of human liver fructose-6-phosphate-2-kinase:fructose-2,6-bisphosphatase.

Amino Acid Sequence↗
PubMed1990

Nucleotide sequence of the fruA gene, encoding the fructose permease of the Rhodobacter capsulatus phosphotransferase system, and analyses of the deduced protein sequence.

The nucleotide sequence of the fruA gene, the terminal gene in the fructose operon of Rhodobacter capsulatus, is reported. This gene codes for the fructose permease (molecular weight, 58,575; 578 aminoacyl residues), the fructose enzyme II (IIFru) of the phosphoenolpyruvate-dependent phosphotransferase system. The deduced aminoacyl sequence of the encoded gene product was found to be 55% identical throughout most of its length with the fructose enzyme II of Escherichia coli, with some regions strongly conserved and others weakly conserved. Sequence comparisons revealed that the first 100 aminoacyl residues of both enzymes II were homologous to the second 100 residues, suggesting that an intragenic duplication of about 300 nucleotides had occurred during the evolution of IIFru prior to divergence of the E. coli and R. capsulatus genes. The protein contains only two cysteyl residues, and only one of these residues is conserved between the two proteins. This residue is therefore presumed to provide the active-site thiol group which may serve as the phosphorylation site. IIFru was found to exhibit regions of homology with sequenced enzymes II from other bacteria, including those specific for sucrose, beta-glucosides, mannitol, glucose, N-acetylglucosamine, and lactose. The degree of evolutionary divergence differed for different parts of the proteins, with certain transmembrane segments exhibiting high degrees of conservation. The hydrophobic domain of IIFru was also found to be similar to several uniport and antiport transporters of animals, including the human and mouse insulin-responsive glucose facilitators. These observations suggest that the mechanism of transmembrane transport may be similar for permeases catalyzing group translocation and facilitated diffusion.

Amino Acid Sequence↗
PubMed1989

Nickel deficiency gives rise to the defective hydrogenase phenotype of hydC and fnr mutants in Escherichia coli.

Hydrogenase activity and other hydrogenase-related functions can be restored to hydC mutants by the specific addition of nickel salts to the growth medium. These mutants are defective in all three hydrogenase isoenzymes and the restoration is dependent upon protein synthesis. The cellular nickel content of the mutant when grown in LB medium is less than 1% of that of the parental strain. Partial suppression of the hydrogenase phenotype of hydC mutants occurs when growth takes place in a different medium. This correlates with an increased cellular nickel content. The phenotype of the mutant is also fully suppressed by growth in media of very low magnesium content. Such media facilitate nickel uptake via the magnesium transport system, which leads to the acquisition of a normal cellular nickel content. Mutations in the fnr gene, which encodes a transcriptional regulator for several anaerobically expressed enzymes, abolishes hydC expression and gives rise to a defective hydrogenase phenotype. The hydrogenase phenotype of fnr is closely similar to that of hydC in all respects examined. The hydrogenase activity of fnr strains can be restored by the presence of a functional hydC gene on a multicopy plasmid. The hydrogenase phenotype of fnr strains therefore arises indirectly via suppression of hydC, which leads to a low cellular nickel content. Nickel has no influence on fumarate reductase or nitrate reductase activities in fnr strains. The hydrogen-metabolism phenotype of fnr strains is, therefore, dependent upon their ability to acquire nickel from growth media. It is likely that hydC encodes a specific transport system for nickel.

Escherichia coli↗
PubMed1987

Regulation of the fdhF gene encoding the selenopolypeptide for benzyl viologen-linked formate dehydrogenase in Escherichia coli.

Two classes of mutants defective in benzyl viologen-linked formate dehydrogenase (FDH-BV) activity were isolated from Escherichia coli K12. Class I consisted of four mutants which were specifically devoid of FDH-BV activity. Their mutation mapped between the ssb and melA genes at 92 min on the genome, at a site recently designated fdhF by Pecher et al. (1985). The direction of transcription of gene fdhF was found to be counterclockwise on the E. coli chromosome in one Mudl(Aprlac) fusion mutant. Expression of the lac operon in this mutant was induced by formate and repressed by nitrate, nitrite or trimethylamine N-oxide. It was found to be dependent on the positive control exerted by the fdhA, B and C genes, possibly involved in selenium incorporation, and by an hydB gene affecting the formate hydrogenlyase pathway. Class II, represented by one Mudl(Aprlac) mutant, exhibited no FDH-BV activity and a reduced level of hydrogenase activity. The relevant fdv mutation was shown to be located at 58 min and to affect the expression of fdhF.

Aldehyde Oxidoreductases↗
PubMed1987

Characterization of the product of the cloned fdhF gene of Escherichia coli.

Random insertions of mini-MudII1734 lac gene fusion bacteriophage were constructed on plasmid pLW06, which carries the fdhF gene coding for benzyl-viologen-linked formate dehydrogenase. They allowed us to limit the size of the gene to a 3 kb fragment and to define its direction of transcription. The identification of the fdhF product as a 85 kDa protein was achieved after expression of derivative plasmids in a maxicell system.

Aldehyde Oxidoreductases↗
PubMed1986

Genetic and physiological characterization of new Escherichia coli mutants impaired in hydrogenase activity.

The Mu dl (ApR lac) bacteriophage was used to generate mutants of Escherichia coli which were defective in formate hydrogenlyase. Three mutants were chosen for further analysis: they lacked hydrogenase (hydrogen: benzyl viologen oxidoreductase) activity, but produced normal levels of fumarate reductase activity and two- to three-fold reduced levels of benzyl viologen (BV)-dependent formate dehydrogenase activity. Two of them (hydC) were shown to contain about 4-fold reduced amounts of formate hydrogenlyase and fumarate-dependent H2 uptake activities. The third one (hydD) was totally devoid of both activities. Their insertion sites were located at 77 min on the E. coli map. Subdivision of these mutants into two classes was subsequently based on the restoration capacity of hydrogenase activity with high concentration of nickel in the growth media. Addition of 500 microM NiCl2 led to a complete recovery of hydrogenase activity, and to the concomitant restoration of normal BV-linked formate dehydrogenase, formate hydrogenlyase and fumarate-dependent H2 uptake activities in the hydC mutants. The hydD mutant was insensitive to the effect of nickel. Expression of the lac operon in hydC and hydD mutants was induced by anaerobiosis. It was not increased by the addition of formate under anaerobic conditions. The presence of nitrate resulted in slightly reduced beta-galactosidase activities in the hydC mutants, whereas those found in the hydD mutant reached only one third of the level obtained in its absence. Fumarate had no effect on both classes. Moreover, in contrast to the hydD locus, the hydC::Mu dl fusions were found to be dependent upon the positive control exerted by the nirR gene product and were totally repressed by an excess of nickel. In addition, the low levels of overall hydrogenase-dependent activities found in a nirR strain were also relieved by the presence of nickel. Our results strongly suggest that the pleiotropic regulatory gene nirR is essential for the expression of a gene (hydC) involved in either transport or processing of nickel in the cell, whose alteration leads to a loss of hydrogenase activity.

Alleles↗