The cyanobacterial hydrogenases can functionally be divided into two groups; uptake hydrogenases, dimeric HupSL, that consumes H2, and bi-directional hydrogenases, pentameric HoxYHEFU, that can both consume and produce H2 [3]. In the case of Nostoc PCC 7120 both hydrogenases may be present, while Nostoc punctiforme only contains the uptake hydrogenase [3, 5]. The cyanobacterial uptake hydrogenase is closely connected to both the N2-fixing process and the occurrence of a nitrogenase, recycling the H2 and thereby

regaining energy and electrons. The LGX818 order function of the bi-directional hydrogenase is more unclear and suggestions range from functioning as a mediator of reducing power during anaerobic conditions to it being part of respiratory complex I [3]. Both types of hydrogenases

go through an extensive maturation process that involves several different accessory proteins. Even though much is still to be learned about this maturation process in Selleck CCI-779 cyanobacteria, comprehensive studies in other organisms like Escherichia coli have been performed [6, 7]. Particularly the large subunit of [NiFe]-hydrogenase (HupL and HoxH in cyanobacteria) requires numerous accessory proteins responsible for metal transport, biosynthesis and insertion of the metal atoms nickel and iron into its active site. The genes encoding for these proteins are usually referred to as the hyp-genes and have been identified in many organisms including several cyanobacterial strains [3]. The Hyp-proteins are considered unspecific and there is usually only one set of hyp-genes irrespective of the number hydrogenases in a single strain [8, 9]. It was recently suggested that a set of protein encoding genes

within the extended hyp-operon of Nostoc PCC 7120 may be involved in the maturation of the small subunit of the cyanobacterial uptake hydrogenase [10]. The final step in the maturation process of the large subunit is a proteolytic cleavage of the C-terminal, which results in a conformational change, and the association of the large subunit to the small subunit [11, 12]. The number of amino acids that are cleaved off varies between different hydrogenases and organisms but the cleavage always takes place after the conserved motif DPCXXCXXH/R resulting in the histidine being the new C-terminal amino Methocarbamol acid [11–14]. Several experiments together with sequencing data have indicated that these putative proteases, contrary to the Hyp-proteins, are specific to different hydrogenases; not only to hydrogenases in different bacterial strains but also to different hydrogenases within the same strain [12, 15]. In both Nostoc punctiforme and Nostoc PCC 7120 putative proteases have been identified through secondary and tertiary structure alignments [16]. The protein product of the gene hupW is believed to process HupL (the large subunit of the uptake hydrogenase) and can be found in both cyanobacterial strains.