CeBiTec Colloquium

(non-scheduled)

 date 

Wednesday, March 24th 2010, 16 c.t.

 location 

G2-104, CeBiTec Building

 speaker 

Prof. Dr. Peter Lindblad

Department of Photochemistry & Molecular Science, Uppsala University, (Sweden)

 title 

Transcriptional regulation and maturation of cyanobacterial hydrogenases

  In cyanobacteria three enzymes are directly involved in the hydrogen metabolism: a nitrogenase that produces H2 as a by-product of nitrogen fixation, an uptake hydrogenase (HupSL, encoded by hupSL) that recaptures H2 and oxidize it, and a bidirectional hydrogenase (encoded by hoxEFUYH, forming an enzyme with a hydrogenase part, HoxYH, and an electron transfer partner protein, HoxEFU) that can both oxidize and produce H2. The transcription of cyanobacterial hup and hox operons are known to be regulated. The maturation of hydrogenases into active enzymes is a complex process and eg a correctly assembled active site requires the involvement of at least seven proteins, encoded by hypABCDEF and a hydrogenase specific protease, encoded by either hupW or hoxW.
Generally, little is known about the transcriptional regulation of cyanobacterial uptake hydrogenases. We showed that NtcA has a specific affinity to a region of the hupSL promoter of Nostoc punctiforme. Truncated versions of the promoter region of the hupSL operon were fused to gfp. All constructs showed heterocyst specific expression. Unexpectedly, the shortest promoter fragment, covering 57 bp upstream and 258 bp downstream the TSP, exhibited the highest promoter activity. The cyanobacterial hox genes have been characterised in some strains. LexA interacts with the promoter region of the hox operon in Synechocystis PCC 6803. The hox genes of Nostoc PCC 7120 are transcribed as two different clusters with LexA interacting with both promoter regions. DNA affinity assays also identified an AbrB-type DNA-binding protein as interacting directly with the promoter region of the hox operon in Synechocystis PCC 6803. This protein binds to the its own promoter region and the promoter region of the hox operon, suggested to function as a positive regulator of hox gene expression. The presence and expression of hyp genes were examined in the N2-fixing cyanobacterium Nostoc PCC 7120. RT-PCRs demonstrated that the six hyp genes may be transcribed as a single operon. TSPs were identified 280 bp upstream from hypF and 445 bp upstream of hypC, respectively. Five upstream ORFs located in between hupSL and the hyp operon, and two downstream ORFs from the hyp genes were shown to be part of the same transcript unit. Recently, the CyAbrB protein CalA (Alr0946) was shown to interact with the regulatory region of hypC and acts as a repressor of its transcription in the cyanobacterium Nostoc 7120. Transcriptional analyses were performed of hupW in Nostoc punctiforme, and hupW and hoxW in Nostoc PCC 7120. Several transcriptional start points together with putative binding sites for NtcA (hupW) and LexA (hoxW) were identified. A phylogenetic tree of hupW & hoxW showed a striking resemblance to the subgroups previously described for [NiFe]-hydrogenases.
Significant advances have been made in the understanding the transcriptional regulations and the maturation of cyanobacterial hydrogenases, needed knowledge when designing cyanobacterial cells for a direct production of renewable H2 from solar energy and water.
 host 

Prof. Dr. Olaf Kruse