Biomedical subjects

Thomas Happe

Publications and source records attributed to Thomas Happe.

13 recordsLinked to original sources

PubMed2005

Autotrophic and mixotrophic hydrogen photoproduction in sulfur-deprived chlamydomonas cells.

In Chlamydomonas reinhardtii cells, H2 photoproduction can be induced in conditions of sulfur deprivation in the presence of acetate. The decrease in photosystem II (PSII) activity induced by sulfur deprivation leads to anoxia, respiration becoming higher than photosynthesis, thereby allowing H2 production. Two different electron transfer pathways, one PSII dependent and the other PSII independent, have been proposed to account for H2 photoproduction. In this study, we investigated the contribution of both pathways as well as the acetate requirement for H2 production in conditions of sulfur deficiency. By using 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), a PSII inhibitor, which was added at different times after the beginning of sulfur deprivation, we show that PSII-independent H2 photoproduction depends on previously accumulated starch resulting from previous photosynthetic activity. Starch accumulation was observed in response to sulfur deprivation in mixotrophic conditions (presence of acetate) but also in photoautotrophic conditions. However, no H2 production was measured in photoautotrophy if PSII was not inhibited by DCMU, due to the fact that anoxia was not reached. When DCMU was added at optimal starch accumulation, significant H2 production was measured. H2 production was enhanced in autotrophic conditions by removing O2 using N2 bubbling, thereby showing that substantial H2 production can be achieved in the absence of acetate by using the PSII-independent pathway. Based on these data, we discuss the possibilities of designing autotrophic protocols for algal H2 photoproduction.

Acetates↗

PubMed2005

Homologous and heterologous overexpression in Clostridium acetobutylicum and characterization of purified clostridial and algal Fe-only hydrogenases with high specific activities.

Clostridium acetobutylicum ATCC 824 was selected for the homologous overexpression of its Fe-only hydrogenase and for the heterologous expressions of the Chlamydomonas reinhardtii and Scenedesmus obliquus HydA1 Fe-only hydrogenases. The three Strep tag II-tagged Fe-only hydrogenases were isolated with high specific activities by two-step column chromatography. The purified algal hydrogenases evolve hydrogen with rates of around 700 micromol H(2) min(-1) mg(-1), while HydA from C. acetobutylicum (HydA(Ca)) shows the highest activity (5,522 micromol H(2) min(-1) mg(-1)) in the direction of hydrogen uptake. Further, kinetic parameters and substrate specificity were reported. An electron paramagnetic resonance (EPR) analysis of the thionin-oxidized HydA(Ca) protein indicates a characteristic rhombic EPR signal that is typical for the oxidized H cluster of Fe-only hydrogenases.

Chlorophyta↗

PubMed2004

Genomics of green algal hydrogen research.

This article summarizes knowledge on genes and their respective proteins in the field of green algal hydrogen research. Emphasis is placed on recently cloned genes from the unicellular green alga Chlamydomonas reinhardtii, including HydA1 and HydA2, which encode homologous [Fe]-hydrogenases, Tla1, which encodes a chlorophyll antenna size regulatory gene, SulP, which encodes a chloroplast sulfate permease, and Sta7, which encodes an isoamylase. Analysis of the structure and function of these genes and of their respective proteins in C. reinhardtii, and related unicellular green algae, is presented in light of the role they play in the hydrogen metabolism in these organisms. A discussion is offered as to the potential application of these genes in the field of hydrogen photoproduction.

Journal Article↗

PubMed2004

Trails of green alga hydrogen research - from hans gaffron to new frontiers.

This paper summarizes aspects of the history of photosynthetic hydrogen research, from the pioneering discovery of Hans Gaffron over 60 years ago to the potential exploitation of green algae in commercial H(2)-production. The trail started as a mere scientific curiosity, but promises to be a most important discovery, one that leads photosynthesis research to important commercial applications. Progress achieved in the field of photosynthetic hydrogen production by green algae includes elucidation of the mechanism, the ability to modify photosynthesis by physiological means and to produce bulk amounts of H(2) gas, and cloning of the [Fe]-hydrogenase genes in several green algal species.

Journal Article↗

PubMed2003

Cyanobacterial H(2) production -- a comparative analysis.

Several unicellular and filamentous, nitrogen-fixing and non-nitrogen-fixing cyanobacterial strains have been investigated on the molecular and the physiological level in order to find the most efficient organisms for photobiological hydrogen production. These strains were screened for the presence or absence of hup and hox genes, and it was shown that they have different sets of genes involved in H(2) evolution. The uptake hydrogenase was identified in all N(2)-fixing cyanobacteria, and some of these strains also contained the bidirectional hydrogenase, whereas the non-nitrogen fixing strains only possessed the bidirectional enzyme. In N(2)-fixing strains, hydrogen was mainly produced by the nitrogenase as a by-product during the reduction of atmospheric nitrogen to ammonia. Therefore, hydrogen production was investigated both under non-nitrogen-fixing conditions and under nitrogen limitation. It was shown that the hydrogen uptake activity is linked to the nitrogenase activity, whereas the hydrogen evolution activity of the bidirectional hydrogenase is not dependent or even related to diazotrophic growth conditions. With regard to large-scale hydrogen evolution by N(2)-fixing cyanobacteria, hydrogen uptake-deficient mutants have to be used because of their inability to re-oxidize the hydrogen produced by the nitrogenase. On the other hand, fermentative H(2) production by the bidirectional hydrogenase should also be taken into account in further investigations of biological hydrogen production.

Biological Transport↗

PubMed2003

Expression of two [Fe]-hydrogenases in Chlamydomonas reinhardtii under anaerobic conditions.

We have isolated and characterized a second [Fe]-hydrogenase gene from the green alga, Chlamydomonas reinhardtii. The HydA2 gene encodes a protein of 505 amino acids that is 74% similar and 68% identical to the known HydA1 hydrogenase from C. reinhardtii. HydA2 contains all the conserved residues and motifs found in the catalytic core of the family of [Fe]-hydrogenases. We demonstrate that both the HydA1 and the HydA2 transcripts are expressed upon anaerobic induction, achieved either by neutral gas purging or by sulfur deprivation of the cultures. Furthermore, the expression levels of both transcripts are regulated (in some cases differently) by incubation conditions, such as the length of anaerobiosis, the readdition of O2, the presence of acetate, and/or the absence of nutrients such as sulfate during growth. Antibodies specific for HydA2 recognized a protein of about 49 kDa in extracts from anaerobically induced C. reinhardtii cells, strongly suggesting that HydA2 encodes for an expressed protein. Homology-based 3D modeling of the HydA2 hydrogenase shows that its catalytic site models well to the known structure of Clostridium pasteurianum CpI, including the H2-gas channel. The major differences between HydA1, HydA2 and CpI are the absence of the N-terminal Fe-S centers and the existence of extra sequences in the algal enzymes. To our knowledge, this work represents the first systematic study of expression of two algal [Fe]-hydrogenases in the same organism.

Amino Acid Sequence↗

PubMed2002

Molecular cloning and characterization of hetR genes from filamentous cyanobacteria.

HetR, a serine type protease, plays an important role in heterocyst differentiation in filamentous cyanobacteria. We isolated and sequenced the hetR genes from different heterocystous and filamentous nonheterocystous cyanobacteria. The hetR gene in the heterocyst forming Anabaena variabilis ATCC 29413 FD was interrupted by interposon mutagenesis (mutant strain WSIII8). This mutant does not form heterocysts and shows no diazotrophic growth under aerobic conditions. However, under anaerobic N(2)-fixing conditions, the WSIII8 cells are able to grow, and high nitrogenase (Nif2) activity is detectable. Nif2 expression was demonstrated in each vegetative cell of the filament by immunolocalization 4 h after nitrogen step-down.

Amino Acid Sequence↗

PubMed2002

Isolation and molecular characterization of the [Fe]-hydrogenase from the unicellular green alga Chlorella fusca.

[Fe]-hydrogenases are redoxenzymes that catalyze the reversible reduction of protons to hydrogen. Hydrogenase activity was observed in a culture of the unicellular green alga Chlorella fusca after an anaerobic incubation, but not in the related species Chlorella vulgaris. Specific polymerase chain reaction (PCR) techniques lead to the isolation of the cDNA and the genomic DNA of a special type of [Fe]-hydrogenase in C. fusca. The functional [Fe]-hydrogenase was purified to homogeneity and its N-terminus was sequenced. The polypeptide sequence shows a high degree of identity with the amino acid sequence deduced from the respective cDNA region. Structural and biochemical analyses indicate that ferredoxin is the main physiological electron donor.

Algal Proteins↗

PubMed2002

HoxE--a subunit specific for the pentameric bidirectional hydrogenase complex (HoxEFUYH) of cyanobacteria.

NAD(P)(+)-reducing hydrogenases have been described to be composed of a diaphorase (HoxFU) and a hydrogenase (HoxYH) moiety. This study presents for the first time experimental evidence that in cyanobacteria, a fifth subunit, HoxE, is part of this bidirectional hydrogenase. HoxE exhibits sequence identities to NuoE of respiratory complex I of Escherichia coli. The subunit composition of the cyanobacterial bidirectional hydrogenase has been investigated. The oxygen labile enzyme complex was purified to close homogeneity under anaerobic conditions from Synechocystis sp. PCC 6803 and Synechococcus sp. PCC 6301. The 647-fold and 1290-fold enriched purified enzyme has a specific activity of 46 micromol H(2) evolved (min mg protein)(-1) and 15 micromol H(2) evolved (min mg protein)(-1), respectively. H(2)-evolution of the purified enzyme of S. sp. PCC 6803 is highest at 60 degrees C and pH 6.3. Immunoblot experiments, using a polyclonal anti-HoxE antibody, demonstrate that HoxE co-purifies with the hydrogenase activity in S. sp. PCC 6301. SDS-PAGE gels of the purified enzymes revealed six proteins, which were partially sequenced and identified, besides one nonhydrogenase component, as HoxF, HoxU, HoxY, HoxH and, remarkably, HoxE. The molecular weight of the native protein (375 kDa) indicates a dimeric assembly of the enzyme complex, Hox(EFUYH)(2).

Amino Acid Sequence↗

PubMed2002

Biochemical and morphological characterization of sulfur-deprived and H2-producing Chlamydomonas reinhardtii (green alga).

Sulfur deprivation in green algae causes reversible inhibition of photosynthetic activity. In the absence of S, rates of photosynthetic O2 evolution drop below those of O2 consumption by respiration. As a consequence, sealed cultures of the green alga Chlamydomonas reinhardtii become anaerobic in the light, induce the "Fe-hydrogenase" pathway of electron transport and photosynthetically produce H2 gas. In the course of such H2-gas production cells consume substantial amounts of internal starch and protein. Such catabolic reactions may sustain, directly or in directly, the H2-production process. Profile analysis of selected photosynthetic proteins showed a precipitous decline in the amount of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) as a function of time in S deprivation, a more gradual decline in the level of photosystem (PS) II and PSI proteins, and a change in the composition of the PSII light-harvesting complex (LHC-II). An increase in the level of the enzyme Fe-hydrogenase was noted during the initial stages of S deprivation (0-72 h) followed by a decline in the level of this enzyme during longer (t >72 h) S-deprivation times. Microscopic observations showed distinct morphological changes in C. reinhardtii during S deprivation and H2 production. Ellipsoid-shaped cells (normal photosynthesis) gave way to larger and spherical cell shapes in the initial stages of S deprivation and H2 production, followed by cell mass reductions after longer S-deprivation and H2-production times. It is suggested that, under S-deprivation conditions, electrons derived from a residual PSII H2O-oxidation activity feed into the hydrogenase pathway, thereby contributing to the H2-production process in Chlamydomonas reinhardtii. Interplay between oxygenic photosynthesis, mitochondrial respiration, catabolism of endogenous substrate, and electron transport via the hydrogenase pathway is essential for this light-mediated H2-production process.

Anaerobiosis↗

PubMed2002

Iron hydrogenases--ancient enzymes in modern eukaryotes.

The distribution of [Fe]-hydrogenases was once thought to be limited to a small number of bacteria and a few peculiar hydrogen-producing anaerobic eukaryotes. However, it is now clear that [Fe]-hydrogenases are more widely distributed among eukaryotes than reports of hydrogen production have suggested. Indeed, genes bearing the hallmark signatures of [Fe]-hydrogenases are found both in our own genome and in the genomes of other higher eukaryotes. At present, the functions of most of these new proteins remain unknown; it is not even known whether they can all make hydrogen. Radical new hypotheses have suggested that hydrogenases played a key role in the formation of the eukaryotic cell. These unique enzymes have thus moved from the margins of eukaryotic biology to become the focus of intense speculation and interest. This article summarizes current knowledge of their distribution, evolution and biochemistry.

Animals↗

PubMed2002

Hydrogenases in green algae: do they save the algae's life and solve our energy problems?

Green algae are the only known eukaryotes with both oxygenic photosynthesis and a hydrogen metabolism. Recent physiological and genetic discoveries indicate a close connection between these metabolic pathways. The anaerobically inducible hydA genes of algae encode a special type of highly active [Fe]-hydrogenase. Electrons from reducing equivalents generated during fermentation enter the photosynthetic electron transport chain via the plastoquinone pool. They are transferred to the hydrogenase by photosystem I and ferredoxin. Thus, the [Fe]-hydrogenase is an electron 'valve' that enables the algae to survive under anaerobic conditions. During sulfur deprivation, illuminated algal cultures evolve large quantities of hydrogen gas, and this promises to be an alternative future energy source.

Aerobiosis↗

PubMed2002

Differential regulation of the Fe-hydrogenase during anaerobic adaptation in the green alga Chlamydomonas reinhardtii.

Chlamydomonas reinhardtii, a unicellular green alga, contains a hydrogenase enzyme, which is induced by anaerobic adaptation of the cells. Using the suppression subtractive hybridization (SSH) approach, the differential expression of genes under anaerobiosis was analyzed. A PCR fragment with similarity to the genes of bacterial Fe-hydrogenases was isolated and used to screen an anaerobic cDNA expression library of C. reinhardtii. The cDNA sequence of hydA contains a 1494-bp ORF encoding a protein with an apparent molecular mass of 53.1 kDa. The transcription of the hydrogenase gene is very rapidly induced during anaerobic adaptation of the cells. The deduced amino-acid sequence corresponds to two polypeptide sequences determined by sequence analysis of the isolated native protein. The Fe-hydrogenase contains a short transit peptide of 56 amino acids, which routes the hydrogenase to the chloroplast stroma. The isolated protein belongs to a new class of Fe-hydrogenases. All four cysteine residues and 12 other amino acids, which are strictly conserved in the active site (H-cluster) of Fe-hydrogenases, have been identified. The N-terminus of the C. reinhardtii protein is markedly truncated compared to other non-algal Fe-hydrogenases. Further conserved cysteines that coordinate additional Fe-S-cluster in other Fe-hydrogenases are missing. Ferredoxin PetF, the natural electron donor, links the hydrogenase from C. reinhardtii to the photosynthetic electron transport chain. The hydrogenase enables the survival of the green algae under anaerobic conditions by transferring the electrons from reducing equivalents to the enzyme.

Adaptation, Physiological↗