The protein docking results, performed with hydrogenases and proteases from several organisms, places the HOXBOX alternatively the corresponding region continuously in unfavourable positions
for C-terminal cleavage making its selleck possible function as a catalytic site learn more unlikely. Added to the already mentioned observation that this region exist in two variations (i.e. the HOXBOX or D(G/C/F)GT) it seems more reasonable it is involved in substrate binding and recognition and might even be important for the proteases specificity. It should be mentioned that these protein-docking studies are mostly performed with 3D-models constructed through protein threading since no crystallised hydrogenase and protease exist from the same organism. Even though the proteins used in this study are related, the sequence identities are sometimes low (20–25%) but increases in the putative docking areas (30–40%). The large subunit of the hydrogenase is also believed to exist in an open conformation, STAT inhibitor which probably makes the nickel associated to the active site of the hydrogenase accessible for the protease . An open conformation could have an immense effect on any kind of protease-hydrogenase interaction but is with today’s knowledge impossible to predict. Conclusion An understanding of the transcriptional regulation of hydrogenase specific proteases in cyanobacteria is starting to
emerge. It suggests that the hydrogenase specific proteases in cyanobacteria are under very similar regulatory control as the hydrogenases
they cleave. The two proteins also appear to have a close physical interaction during the cleavage moment, which could explain the specificity seen among proteases and the resemblance seen between the protease and the hydrogenase phylogenetic trees, and this interaction might be of very ancient origin. After comparing the phylogenetic tree of hydrogenases and their specific proteases we suggest that a group 3 hydrogenase spread through HGT to the bacterial domain, probably together with a hydrogenase specific protease indicating that the proteolytic cleavage first evolved within group 3a/4 hydrogenases. We also propose that all 3d-type hydrogenases within bacteria evolved from this group 3 hydrogenase and therefore are the result of the same HGT event. Finally the novel observation of the so called HOXBOX may help in understanding the Resveratrol specificity seen among hydrogenase specific proteases and is an interesting target for further studies. Methods Bacterial strains and culture conditions Cyanobacterial strains used in these experimental studies, Nostoc sp. strain PCC 7120 (also known as Anabaena sp. strain PCC 7120) , and Nostoc punctiforme ATCC 29133 (also known as Nostoc sp. strain PCC 73102)  were grown in BG11o medium (N2-fixing cultures) at 30°C under continuous light (40 μmol photons s-1m-2) and by sparging with air as previously described . For non N2-fixing growth (cultures with no heterocysts) NH4Cl (2.5 mM) and MOPS (0.