An AbrB-Like Protein Regulates the Expression of the Bidirectional Hydrogenase in Synechocystis sp. Strain PCC 6803

Abstract

In the unicellular cyanobacterium Synechocystis sp. strain PCC 6803, the pentameric bidirectional Ni-Fe hydrogenase (HoxEFUYH) is the sole enzyme involved in hydrogen metabolism. Recent investigations implicated the transcription factor LexA in the regulation of the hox genes in this cyanobacterium, suggesting the factor to work as an activator. In this work, we show evidence that LexA cannot account exclusively for the regulation of the hox genes in this cyanobacterium. Therefore, we investigated which additional transcription factors interact in and may regulate the expression of the hox genes in Synechocystis sp. strain PCC 6803. By using DNA affinity assays, a transcription factor with similarity to the transition state regulator AbrB from Bacillus subtilis was isolated. Electrophoretic mobility shift assays showed that the AbrB-like protein specifically interacts with the promoter region of the hox genes as well as with its own promoter region. In addition, results obtained with two genetically modified strains of Synechocystis sp. strain PCC 6803, one with a not fully segregated inactivation mutation of the abrB-like gene and the other overexpressing the same abrB-like gene, suggest that this transcription factor functions as a regulator of hox gene expression.Two different Ni-Fe hydrogenases have been characterized physiologically, biochemically, and on the molecular level in cyanobacteria: one is named uptake hydrogenase and catalyzes the consumption of H 2 produced by the nitrogenase during N 2 fixation, and the other is termed bidirectional hydrogenase and its function is still under debate (32,37,38).Over the years, it has continuously been shown by reverse transcription-PCR and Northern blot analysis (2,3,4,15,23,27,33,38) that the transcription of cyanobacterial hydrogenases varies under different environmental conditions. Nevertheless, an understanding of which key regulators are involved is just emerging and the inherent signal transduction pathways certainly deserve better attention. Therefore, it is imperative to study the mechanisms controlling the expression of both cyanobacterial hydrogenases more closely in order to acquire an improved comprehension of their functions and also to develop novel tools for enhancing a sustainable and reliable production of H 2 from cyanobacteria (38).Recently, the first reports on the transcription factors involved in the regulation of cyanobacterial hydrogenases became available. NtcA, the nitrogen control regulator in cyanobacteria, has been suggested to mediate the transcription of the uptake hydrogenase in different cyanobacterial strains, Nostoc punctiforme PCC 73102 (24), Gloeothece sp. strain ATCC 27152 (27), and Lyngbya majuscula CCAP 1446/4 (23), as well as that of the hydrogenase maturation proteins in Lyngbya majuscula CCAP 1446/4 (15). A LexA-related protein, which has been proposed to not be involved in the classical regulation of DNA repair genes (11), was shown to interact in two different regions of the promoter of the hox genes in Synechocystis...

Gene expression under low-oxygen conditions in the cyanobacterium Synechocystis sp. PCC 6803 demonstrates Hik31-dependent and -independent responses

“…This was consistent with the finding that Sll1626 interacts with the hox promoter and positively regulates its expression (Oliveira & Lindblad, 2005). The genes encoding Sll0359 and Sll0882 are also regulators of the hox operon (Ishii & Hihara, 2008;Oliveira & Lindblad, 2008), these genes are not upregulated under low-oxygen conditions, but may play a role in regulation.…”

An experimentally anchored map of transcriptional start sites in the model cyanobacterium Synechocystis sp. PCC6803

“…4 shows the hydrogenase operon which encodes all proteins required for pentameric bidirectional Ni-Fe hydrogenase (HoxEFUYH). This operon uses a single TSS located 168 nt upstream of hoxE (19), and its regulation is well studied (19)(20)(21). Intriguingly, we found that the operon is framed by two highly expressed ncRNAs, one of which [SyR1 (14)], was strongly upregulated under high light, whereas the other (ncr0700) was maximally expressed in the dark (Fig.…”

CalA, a cyAbrB protein, binds to the upstream region of ftsZ and is down-regulated in heterocysts in Anabaena sp. PCC 7120

“…The great reduction of CalA in heterocysts appeared to be directly related to the down-regulation of ftsZ. Like sll0359 in Synechocystis 6803 (Oliveira and Lindblad 2008;Ishii and Hihara 2008), calA is essential to the viability of Anabaena 7120. An interrupted mutant of calA could not be segregated, while the C.K-P petE -calA mutant was readily segregated.…”

“…The two cyAbrBs in Synechocystis sp. PCC 6803 (referred to as Synechocysits 6803 hereafter) have been shown to bind to the promoter regions of the hox operon encoding the bidirectional NiFe hydrogenase (Oliveira and Lindblad 2008), nitrogen-regulated genes (Ishii and Hihara 2008), low CO 2 -responsive genes (Lieman-Hurwitz et al 2009) and to affect their expression. One of the two cyAbrBs in Anabaena 7120, Alr0946 (CalA), has been shown to bind to the upstream regions of hypC, a gene encoding a hydrogenase assembly chaperone, alr0946-alr0947 and to repress their transcription (Agervald et al 2010).…”