RESUMO
Cyanobacteria may possess several enzymes that are directly involved in dihydrogen metabolism: nitrogenase(s) catalyzing the production of hydrogen concomitantly with the reduction of dinitrogen to ammonia, an uptake hydrogenase (encoded by hupSL) catalyzing the consumption of hydrogen produced by the nitrogenase, and a bidirectional hydrogenase (encoded by hoxFUYH) which has the capacity to both take up and produce hydrogen. This review summarizes our knowledge about cyanobacterial hydrogenases, focusing on recent progress since the first molecular information was published in 1995. It presents the molecular knowledge about cyanobacterial hupSL and hoxFUYH, their corresponding gene products, and their accessory genes before finishing with an applied aspect--the use of cyanobacteria in a biological, renewable production of the future energy carrier molecular hydrogen. In addition to scientific publications, information from three cyanobacterial genomes, the unicellular Synechocystis strain PCC 6803 and the filamentous heterocystous Anabaena strain PCC 7120 and Nostoc punctiforme (PCC 73102/ATCC 29133) is included.
Assuntos
Cianobactérias/enzimologia , Hidrogênio/metabolismo , Hidrogenase/metabolismo , Sequência de Aminoácidos , Sequência de Bases , Cianobactérias/genética , Hidrogenase/química , Hidrogenase/genética , Dados de Sequência MolecularRESUMO
This work presents the characterization of an uptake hydrogenase from a marine filamentous nonheterocystous cyanobacterium, Lyngbya majuscula CCAP 1446/4. The structural genes encoding the uptake hydrogenase (hupSL) were isolated and characterized, and regulatory sequences were identified upstream of hupS. In silico analysis highlighted various sets of long repetitive sequences within the hupSL intergenic region and downstream of hupL. The transcriptional regulator that operates global nitrogen control in cyanobacteria (NtcA) was shown to bind to the promoter region, indicating its involvement in the transcriptional regulation of hupSL. Under N2-fixing conditions and a 12-h light/12-h dark regime, H2 uptake activity was shown to follow a daily pattern with a clear maximum towards the end of the dark period, preceded by an increase in the transcript levels initiated in the end of the light phase. Novel antibodies directed against HupL of Lyngbya majuscula CCAP 1446/4 were used to monitor the protein levels throughout the 24-h period. The results suggest that protein turnover occurs, with degradation taking place during the light phase and de novo synthesis occurring during the dark phase, coinciding with the pattern of H2 uptake. Taking into account our results and the established correlation between the uptake hydrogenase activity and N2 fixation in cyanobacteria, it seems probable that both processes are confined to the dark period in aerobically grown cells of Lyngbya majuscula CCAP 1446/4.
Assuntos
Cianobactérias/crescimento & desenvolvimento , Escuridão , Regulação Bacteriana da Expressão Gênica , Hidrogenase/metabolismo , Luz , Óperon , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Sequência de Bases , Cianobactérias/genética , Cianobactérias/metabolismo , Hidrogênio/metabolismo , Hidrogenase/genética , Dados de Sequência Molecular , Fixação de Nitrogênio , Regiões Promotoras Genéticas , Sequências Repetitivas de Ácido Nucleico , Análise de Sequência de DNA , Transcrição GênicaRESUMO
The structural genes (hupSL) encoding an uptake hydrogenase in the unicellular cyanobacterium Gloeothece sp. ATCC 27152, a strain capable of aerobic N(2) fixation, were identified and sequenced. 3'-RACE experiments uncovered the presence of an additional ORF 184 bp downstream of hupL, showing a high degree of sequence identity with a gene encoding an uptake-hydrogenase-specific endopeptidase (hupW) in other cyanobacteria. In addition, the transcription start point was identified 238 bp upstream of the hupS translational start. RT-PCR experiments revealed that hupW is co-transcribed with the uptake hydrogenase structural genes in Gloeothece sp. ATCC 27152. In addition, Northern hybridizations clearly showed that hupSLW are transcribed under nitrogen fixing conditions, but not in the presence of combined nitrogen. A putative NtcA binding site was identified in the promoter region upstream of hupS, centred at -41.5 bp with respect to the transcription start point. Electrophoretic retardation of a labelled DNA fragment (harbouring the putative NtcA-binding motif) was significantly affected by an Escherichia coli cell-free extract containing overexpressed NtcA, suggesting that NtcA is involved in the transcriptional regulation of hupSLW.