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B Friedrich

Publications and source records attributed to B Friedrich.

At least 55 records · Page 3Linked to original sources
PubMed1998

A novel multicomponent regulatory system mediates H2 sensing in Alcaligenes eutrophus.

Oxidation of molecular hydrogen catalyzed by [NiFe] hydrogenases is a widespread mechanism of energy generation among prokaryotes. Biosynthesis of the H2-oxidizing enzymes is a complex process subject to positive control by H2 and negative control by organic energy sources. In this report we describe a novel signal transduction system regulating hydrogenase gene (hox) expression in the proteobacterium Alcaligenes eutrophus. This multicomponent system consists of the proteins HoxB, HoxC, HoxJ*, and HoxA. HoxB and HoxC share characteristic features of dimeric [NiFe] hydrogenases and form the putative H2 receptor that interacts directly or indirectly with the histidine protein kinase HoxJ*. A single amino acid substitution (HoxJ*G422S) in a conserved C-terminal glycine-rich motif of HoxJ* resulted in a loss of H2-dependent signal transduction and a concomitant block in autophosphorylating activity, suggesting that autokinase activity is essential for the response to H2. Whereas deletions in hoxB or hoxC abolished hydrogenase synthesis almost completely, the autokinase-deficient strain maintained high-level hox gene expression, indicating that the active sensor kinase exerts a negative effect on hox gene expression in the absence of H2. Substitutions of the conserved phosphoryl acceptor residue Asp55 in the response regulator HoxA (HoxAD55E and HoxAD55N) disrupted the H2 signal-transduction chain. Unlike other NtrC-like regulators, the altered HoxA proteins still allowed high-level transcriptional activation. The data presented here suggest a model in which the nonphosphorylated form of HoxA stimulates transcription in concert with a yet unknown global energy-responsive factor.

Alcaligenes↗
PubMed1998

The Alcaligenes eutrophus hemN gene encoding the oxygen-independent coproporphyrinogen III oxidase, is required for heme biosynthesis during anaerobic growth.

The insertion mutant HF231 of Alcaligenes eutrophus H16 failed to grow anaerobically on nitrate and nitrite. When grown under oxygen limitation, mutant HF231 specifically excreted coproporphyrin III, an intermediate of heme biosynthesis. With the help of a Tn5-labeled fragment, we identified and cloned the corresponding wild-type fragment. Sequence analysis of the mutant locus revealed an open reading frame consisting of 1,473 bp, predicting a protein of 491 amino acids that corresponds to a size of 54.2 kDa. In the non-coding upstream region, consensus elements that are indicative for binding sites of the anaerobic transcriptional regulator Fnr were identified. The deduced polypeptide showed extensive sequence similarity with various bacterial oxygen-independent coproporphyrinogen III oxidases designated HemN. HemN catalyzes the oxidative decarboxylation of coproporphyrinogen III to yield protoporphyrinogen IX. Anaerobic growth on nitrate and nitrite of mutant HF231 was restored by introducing the hemN gene of A. eutrophus or of Pseudomonas aeruginosa on a broad-host-range vector. Likewise, the A. eutrophus hemN complemented heme biosynthesis of a Salmonella typhimurium hemF/hemN double mutant during anaerobic and aerobic growth. Analysis of a transcriptional lacZ gene fusion showed that expression of hemN in A. eutrophus is nitrate-independent and repressed by oxygen.

Alcaligenes↗
PubMed1998

Duplication of hyp genes involved in maturation of [NiFe] hydrogenases in Alcaligenes eutrophus H16.

Alcaligenes eutrophus H16 harbors seven hyp genes (hypA, B, F, C, D, E, and X) as part of the hydrogenase gene cluster on megaplasmid pHG1. Here we demonstrate that three of the hyp genes (hypA, B, and F) are duplicated in A. eutrophus, which explains the lack of a phenotypic change in single-site mutants impaired in one of the two copies. Mutants with lesions in both copies showed clear alterations in hydrogenase activities. Deletions in hypF1 and hypF2 completely abolished activities of the soluble hydrogenase and of the membrane-bound hydrogenase, mutations in hypA1 and hypA2 totally blocked the membrane-bound hydrogenase activity, while residual soluble hydrogenase activity accounted for the extremely slow growth of the strain on H2. Both hydrogenase activities of mutants defective in hypB1 and hypB2 were partially restored by elevating the concentration of nickel chloride in the medium. Reduction of hydrogenase activities in the double mutants correlated with varying degrees of maturation deficiency based upon the amount of unprocessed nickel-free hydrogenase precursor. Despite a high identity between the two copies of hyp gene products, substantial structural differences were identified between the two copies of hypF genes. HypF1, although functionally active, is a truncated version of HypF2, whose structure resembles HypF proteins of other organisms. Interestingly, the N-terminus of HypF2, which is missing in the HypF1 counterpart, contains a putative acylphosphatase domain in addition to a potential metal binding site.

Bacterial Proteins↗
PubMed1998

hoxX (hypX) is a functional member of the Alcaligenes eutrophus hyp gene cluster.

The role of HoxX in hydrogenase biosynthesis of Alcaligenes eutrophus H16 was re-examined. The previously characterized hoxX deletion mutant HF344 and a newly constructed second hoxX mutant carrying a smaller in-frame deletion were studied. The second mutant was impaired in the activity of both the soluble and the membrane-bound hydrogenase. The two hydrogenase activities were reduced by approximately 50% due to delayed processing of the active-site-containing large subunits, while hydrogenase gene expression was not affected. We conclude that the mutation in mutant HF344 causes polarity resulting in the observed regulatory phenotype of this mutant. The data presented in this report point to an enhancing function of HoxX in the conversion of the soluble hydrogenase and of the membrane-bound hydrogenase large-subunit precursor. Thus, hoxX encodes a member of the Hyp proteins that are required for the formation of active hydrogenase and was accordingly renamed hypX.

Bacterial Proteins↗
PubMed1998

Transcriptional regulation of Alcaligenes eutrophus hydrogenase genes.

Alcaligenes eutrophus H16 produces a soluble hydrogenase (SH) and a membrane-bound hydrogenase (MBH) which catalyze the oxidation of H2, supplying the organism with energy for autotrophic growth. The promoters of the structural genes for the SH and the MBH, PSH and PMBH, respectively, were identified by means of the primer extension technique. Both promoters were active in vivo under hydrogenase-derepressing conditions but directed only low levels of transcription under condition which repressed hydrogenase synthesis. The cellular pools of SH and MBH transcripts under the different growth conditions correlated with the activities of the respective promoters. Also, an immediate and drastic increase in transcript pool levels occurred upon derepression of the hydrogenase system. Both promoters were dependent on the minor sigma factor sigma 54 and on the hydrogenase regulator HoxA in vivo. PSH was stronger than PMBH under both heterotrophic and autotrophic growth conditions. The two promoters were induced at approximately the same rates upon derepression of the hydrogenase system in diauxic cultures. The response regulator HoxA mediated low-level activation of PSH and PMBH in a heterologous system.

Alcaligenes↗
PubMed1998

Subforms and in vitro reconstitution of the NAD-reducing hydrogenase of Alcaligenes eutrophus.

The cytoplasmic, NAD-reducing hydrogenase (SH) of Alcaligenes eutrophus H16 is a heterotetrameric enzyme which contains several cofactors and undergoes a complex maturation during biogenesis. HoxH is the Ni-carrying subunit, and together with HoxY it forms the hydrogenase dimer. HoxF and HoxU represent the flavin-containing diaphorase moiety, which is closely related to NADH:ubiquinone oxidoreductase and mediates NADH oxidation. A variety of mutations were introduced into the four SH structural genes to obtain mutant enzymes composed of monomeric and dimeric forms. A deletion removing most of hoxF, hoxU, and hoxY led to the expression of a HoxH monomer derivative which was proteolytically processed at the C terminus like the wild-type polypeptide. While the hydrogenase dimer, produced by a strain deleted of hoxF and hoxU, displayed H2-dependent dye-reducing activity, the monomeric form did not mediate the activation of H2, although nickel was incorporated into HoxH. Deletion of hoxH and hoxY led to the production of HoxFU dimers which displayed NADH:oxidoreductase activity. Mixing the hydrogenase and the diaphorase moieties in vitro reconstituted the structure and catalytic function of the SH holoenzyme.

Alcaligenes↗
PubMed1997

Functional and structural role of the cytochrome b subunit of the membrane-bound hydrogenase complex of Alcaligenes eutrophus H16.

This study shows that the product of the hoxZ gene of Alcaligenes eutrophus H16 is a b-type cytochrome (cytochrome b(z)), which is essential for anchoring the membrane-bound hydrogenase (MBH) complex to the periplasmic side of the membrane and for H2-coupled respiration. The hoxZ product is not required for MBH translocation and H2-dependent reduction of the redox dye, 2,3,5-triphenyl-2-tetrazolium chloride. The lack of cytochrome b(z) does not affect the electron-transport activities linked to oxidation of succinate and NADH, although it enhances the electron-flow rate through the cytochrome-c oxidase pathway in hoxZdelta membranes. We show that the hoxZ product is a dihaem cytochrome b (haems with E(m7.0) of +10 mV and +166 mV) involved in H2-dependent electron transfer. We conclude that cytochrome b(z) of the A. eutrophus MBH complex is the link necessary for transfer of electrons from H2 to the ubiquinone pool and that it is required for attachment of MBH to the membrane.

Alcaligenes↗
PubMed1997

C-terminal extension of the H2-activating subunit, HoxH, directs maturation of the NAD-reducing hydrogenase in Alcaligenes eutrophus.

Formation of enzymatically active [NiFe] hydrogenases is dependent on a number of posttranslational steps, including metal attachment to a precursor of the catalytic subunit, truncation of a small C-terminal peptide from the precursor, and oligomerisation of the subunits. Two amino acid replacements were introduced by site-directed mutagenesis at the C-terminal proteolytic cleavage site of HoxH, the Ni-containing subunit of the cytoplasmic NAD-reducing hydrogenase of Alcaligenes eutrophus H16. Replacement of Ala465, the first residue of the 24-amino-acid cleaved polypeptide, by Pro yielded a form of HoxH that was blocked in C-terminal proteolysis. This HoxH subunit, although capable of binding Ni, was blocked in formation of a stable tetrameric holoenzyme. In the second mutant, the C-terminal extension of HoxH was eliminated by substituting the Ala codon for a translational stop codon. Although this mutant subunit was able to form the oligomeric holoenzyme, it was devoid of Ni. Both mutant proteins contained only traces of H2-activating functions. H2-dependent reduction of NAD and benzylviologen, and D2/H+-exchange activity were almost completely abolished, while the NADH oxidoreductase activity, mediated by the diaphorase moiety of the hydrogenase, was retained. These results allow the following conclusions: the C-terminal extension of HoxH is neccessary to direct specific Ni insertion into the hydrogenase; subunit assembly to the holoenzyme is not dependent on Ni insertion; and a precursor with the C-terminal peptide is not competent for assembly.

Alcaligenes↗
PubMed1997

Chronic sinusitis refractory to standard management in patients with humoral immunodeficiencies.

Chronic refractory sinusitis is a common feature in patients with primary immunodeficiencies. The efficacy of standard therapeutic strategies is questionable. In an open trial we evaluated the efficacy of azithromycin, N-acetylcysteine and topical intranasal beclomethasone (100 microg twice daily for 6 weeks) in 16 patients with primary immunodeficiencies (median age 13.5 years, range 5-32 years). All patients suffered from chronic sinusitis despite regular immunoglobulin replacement therapy every 3 weeks. Magnetic resonance imaging (MRI) scans were performed before and after 6 weeks of treatment to evaluate morphological changes in the paranasal sinuses. Nasal swabs and washings were taken for microbial analysis and measurement of inflammatory mediators (IL-8, tumour necrosis factor-alpha (TNF-alpha), eosinophilic cationic protein (ECP)) before and post therapy. Inflammatory mediators in nasal secretions were significantly elevated in patients: IL-8 median 2436 pg/ml (range 441-5435 pg/ml), TNF-alpha 37.3 pg/ml (3.75-524 pg/ml) and ECP 33 ng/ml (1.5-250 ng/ml) versus age-matched healthy controls: IL-8 median 212 pg/ml (99-825 pg/ml), TNF-alpha 3.77 pg/ml (2.8-10.2 pg/ml) and ECP 1.5 ng/ml (1.5-14.8 ng/ml) (P < 0.0001). Inflammation of the maxillary sinuses was confirmed by MRI scans in all patients, additionally infection of the ethmoidal and frontal sinuses was recorded in five patients. Bacterial growth appeared in 11 out of 16 cultures. In spite of therapy, no improvement in sinal inflammation visualized by MRI was achieved. Moreover, no significant decrease in pathogens and levels of inflammatory mediators could be detected (IL-8 1141 pg/ml, 426-4556 pg/ml; TNF-alpha 13.9 pg/ml, 4.1-291.6 pg/ml; ECP 32.3 ng/ml, 3.7-58.4 ng/ml). Our results demonstrate that conventional management of sinusitis is of little benefit in patients with chronic refractory sinusitis with an underlying immunodeficiency. More studies are needed to test antibiotic regimens, probably combined with surgical drainage and anti-inflammatory agents.

Acetylcysteine↗
PubMed1997

Structural gene (nirS) for the cytochrome cd1 nitrite reductase of Alcaligenes eutrophus H16.

Denitrification by Alcaligenes eutrophus H16 is genetically linked to megaplasmid pHG1. Unexpectedly, the gene encoding the nitrite reductase (nirS) was identified on chromosomal DNA. The nirS product showed extensive homology with periplasmic nitrite reductases of the heme cd1-type. Disruption of nirS abolished nitrite-reducing ability, indicating that NirS is the enzyme essential for denitrification in A.eutrophus.

Alcaligenes↗
PubMed1997

Two isofunctional nitric oxide reductases in Alcaligenes eutrophus H16.

Two genes, norB and norZ, encoding two independent nitric oxide reductases have been identified in Alcaligenes eutrophus H16. norB and norZ predict polypeptides of 84.5 kDa with amino acid sequence identity of 90%. While norB resides on the megaplasmid pHG1, the norZ gene is located on a chromosomal DNA fragment. Amino acid sequence analysis suggests that norB and norZ encode integral membrane proteins composed of 14 membrane-spanning helices. The region encompassing helices 3 to 14 shows similarity to the NorB subunit of common bacterial nitric oxide reductases, including the positions of six strictly conserved histidine residues. Unlike the Nor enzymes characterized so far from denitrifying bacteria, NorB and NorZ of A. eutrophus contain an amino-terminal extension which may form two additional helices connected by a hydrophilic loop of 203 amino acids. The presence of a NorB/NorZ-like protein was predicted from the genome sequence of the cyanobacterium Synechocystis sp. strain PCC6803. While the common NorB of denitrifying bacteria is associated with a second cytochrome c subunit, encoded by the neighboring gene norC, the nor loci of A. eutrophus and Synechocystis lack adjacent norC homologs. The physiological roles of norB and norZ in A. eutrophus were investigated with mutants disrupted in the two genes. Mutants bearing single-site deletions in norB or norZ were affected neither in aerobic nor in anaerobic growth with nitrate or nitrite as the terminal electron acceptor. Inactivation of both norB and norZ was lethal to the cells under anaerobic growth conditions. Anaerobic growth was restored in the double mutant by introducing either norB or norZ on a broad-host-range plasmid. These results show that the norB and norZ gene products are isofunctional and instrumental in denitrification.

Alcaligenes↗
PubMed1997

A hydrogen-sensing system in transcriptional regulation of hydrogenase gene expression in Alcaligenes species.

Heterologous complementation studies using Alcaligenes eutrophus H16 as a recipient identified a hydrogenase-specific regulatory DNA region on megaplasmid pHG21-a of the related species Alcaligenes hydrogenophilus. Nucleotide sequence analysis revealed four open reading frames on the subcloned DNA, designated hoxA, hoxB, hoxC, and hoxJ. The product of hoxA is homologous to a transcriptional activator of the family of two-component regulatory systems present in a number of H2-oxidizing bacteria. hoxB and hoxC predict polypeptides of 34.5 and 52.5 kDa, respectively, which resemble the small and the large subunits of [NiFe] hydrogenases and correlate with putative regulatory proteins of Bradyrhizobium japonicum (HupU and HupV) and Rhodobacter capsulatus (HupU). hoxJ encodes a protein with typical consensus motifs of histidine protein kinases. Introduction of the complete set of genes on a broad-host-range plasmid into A. eutrophus H16 caused severe repression of soluble and membrane-bound hydrogenase (SH and MBH, respectively) synthesis in the absence of H2. This repression was released by truncation of hoxJ. H2-dependent hydrogenase gene transcription is a typical feature of A. hydrogenophilus and differs from the energy and carbon source-responding, H2-independent mode of control characteristic of A. eutrophus H16. Disruption of the A. hydrogenophilus hoxJ gene by an in-frame deletion on megaplasmid pHG21-a led to conversion of the regulatory phenotype: SH and MBH of the mutant were expressed in the absence of H2 in response to the availability of the carbon and energy source. RNA dot blot analysis showed that HoxJ functions on the transcriptional level. These results suggest that the putative histidine protein kinase HoxJ is involved in sensing molecular hydrogen, possibly in conjunction with the hydrogenase-like polypeptides HoxB and HoxC.

Alcaligenes↗
PubMed1997

Cutaneous inflammation limited to the region of the ulcer in chronic venous insufficiency.

BACKGROUND: The role of inflammatory reactions in the pathogenesis of chronic venous insufficiency and the persistence of venous ulcerations is still not totally clear and remains a hotly debated topic. An investigation of the intensity and distribution of ICAM-1 expression and different inflammatory cells should help clarify whether inflammatory processes are limited locally to the area of the ulcer or if an upregulation can also be observed in clinically unaffected skin of CVI-III patients, as a sign of a primary inflammatory process. PATIENTS AND METHODS: We examined two skin areas in 10 patients with venous ulcerations. One area was at the border of the ulcer and another in clinically unaffected skin (distance from the ulcer: 12.6 +/- 5.1 cm). In addition skin specimens were obtained from the perimalleolar skin of 10 healthy controls. Our histological and immunohistochemical examinations were focused on inflammatory cells (B and T lymphocytes, macrophages, and mast cells) and on the adhesion molecule ICAM-1. RESULTS: A very strong expression of ICAM-1 could be seen at the border of the ulcer. This tissue also showed a dense infiltration, mainly by T lymphocytes and macrophages. In some cases the tissue was infiltrated by an increased number of mast cells. This is the typical picture of a chronic inflammatory reaction. Compared to healthy controls, the clinically unaffected skin of patients showed not an increased expression of ICAM-1 and only in some cases we could find a slight perivascular infiltrate of T lymphocytes. CONCLUSIONS: These data imply that the upregulation of endothelial adhesion molecules (ICAM-1) and dermal infiltration by T lymphocytes and macrophages in CVI-III patients is limited to the region of the ulcer, or at least to skin areas with a severe microangiopathy, and is part of a secondary elimination of necrotic issue (an 'injury and repair' process). These local chronic inflammatory reactions are certainly an important factor in the persistence and recurrence of venous ulcerations.

Adult↗
PubMed1996

hyp gene products in Alcaligenes eutrophus are part of a hydrogenase-maturation system.

In Alcaligenes eutrophus H16 the hyp gene complex consists of six open reading frames hypA1, B1, F1, C, D and E whose products are involved in maturation of the two NiFe hydrogenases: an NAD-reducing cytoplasmic enzyme (SH) and a membrane-bound electron-transport-coupled protein (MBH). hypB1 and hypF1 were originally considered to form a single open reading frame designated hypB [Dernedde, J., Eitinger, M. & Friedrich, B. (1993) Arch. Microbiol. 159, 545-553]. Re-examination of the relevant sequence identified hypB1 and hypF1 as two distinct genes. Non-polar in-frame deletions in the individual hyp genes were constructed in vitro and transferred via gene replacement to the wild-type strain. The resulting mutants fall into two classes. Deletions in hypC, D and E (class I) gave a clear negative phenotype, while hypA1, B1 and F1 deletion mutants (class II) were not impaired in hydrogen metabolism. Class I mutants were unable to grow on hydrogen under autotrophic conditions. The enzymatic activities of SH and MBH were disrupted in all three class I mutants. Immunoblot analysis showed the presence of the H2-activating SH subunit (HoxH) at levels comparable to those observed in the wild-type strain whereas the other three subunits (HoxF, U and Y) were only detectable in trace amounts, probably due to proteolytic degradation. Likewise, MBH was less stable in hypC, D and E deletion mutants and was not attached to the cytoplasmic membrane. In the wild-type strain, HoxH and the MBH large subunit (HoxG) undergo C-terminal proteolytic processing before attaining enzymatic activity. In class I mutants this maturation was blocked. 63Ni-incorporation experiments identified both hydrogenases as nickel-free apoproteins in these mutants. Although class II mutants bearing deletions in hypA1, B1 and F1 showed no alteration of the wild-type phenotype, a role for these genes in the incorporation of nickel and hence hydrogenase maturation cannot be excluded, since there is experimental evidence that this set of genes is duplicated in A. eutrophus.

Alcaligenes↗
PubMed1996

The motor performance test series in Parkinson's disease is influenced by depression.

The Motor Performance Test Series (MPTS) is widely used for treatment control in Parkinson's disease (PD). To elucidate the possible influence of depression on the fine motor skills in PD, 54 patients with idiopathic PD were investigated with the MPTS. 27 patients with major intensity of depression were compared to 27 age and motor disability matched patients with minor symptoms of depression, evaluated by the Zung depression scale. As determined by the subtest aiming, a significant lower ability for precise, quick complex arm-hand movements in depressed Parkinsonian patients was found. This result may be explained partly by motivation deficits in depressed patients with PD. On the other hand impairment of special motor loops including frontal lobe projections to specific thalamic subnuclei or to the caudate nucleus may cause disturbances of the subtest aiming in depressed Parkinsonian patients. On the basis of these findings impaired aiming may be explained by diminished ability for complex, semivoluntary movements in depressive Parkinsonian patients. The influence of psychiatric comorbidity on MPTS subtest aiming has to be considered in further therapy studies using evaluation of motor deficits by MPTS.

Adult↗
PubMed1996

Characterization of the membranous denitrification enzymes nitrite reductase (cytochrome cd1) and copper-containing nitrous oxide reductase from Thiobacillus denitrificans.

Cytochrome cd1-nitrite reductase and nitrous oxide reductase of Thiobacillus denitrificans were purified and characterized by biochemical and immunochemical methods. In contrast to the generally soluble nature of the denitrification enzymes, these two enzymes were isolated from the membrane fraction of T. denitrificans and remained active after solubilization with Triton X-100. The properties of the membrane-derived enzymes were similar to those of their soluble counterparts from the same organism. Nitrous oxide reductase activity was inhibited by acetylene. Nitrite reductase and nitrous oxide reductase cross-reacted with antisera raised against the soluble enzymes from Pseudomonas stutzeri. The nirS, norBC, and nosZ genes encoding the cytochrome cd1-nitrite reductase, nitric oxide reductase, and nitrous oxide reductase, respectively, from P. stutzeri hybridized with genomic DNA from T. denitrificans. Cross-reactivity and similar N-terminal amino acid and gene sequences suggest that the primary structures of the Thiobacillus enzymes are homologous to the soluble proteins from P. stutzeri.

Amino Acid Sequence↗