Thesis presented October 17, 2019

Abstract:
CO dehydrogenase (CODH) is a key enzyme of the water gas shift reaction (WGSR) in hydrogenogenic carboxydotrophs such as Rhodospirillum rubrum, able to use CO as carbon and energy source. A remarkable feature of CODH is the presence of a unique active site, the C-cluster composed of a [NiFe₄S₄] center, of which very little is known about its biogenesis. Nickel insertion is essential for the enzyme activation and it requires the intervention of the accessory proteins CooC, CooJ and CooT, able to supply the nickel into the CODH. Here, I report the results obtained from the characterization of CooT and CooJ. From the CooT family, two CooT were studies: RrCooT and ChCooT. Concerning RrCooT, the peculiarity of its nickel-binding site was unveiled. Ni(II) is coordinated by bis-amidate/bis-thiolate ligands provided by both solvent-exposed Cys2, unprecedented in biology. The X-ray structure of ChCooT, as well as its biophysical characterization, revealed the identification of a “Cys2-His55” nickel-binding motif, highlighting the existence of two distinct Ni-binding modes in the same protein family. RrCooJ is a histidine-rich protein: the structural characterization of a truncated version lacking the His-tail enabled us to identify the presence of two nickel binding sites: a “high-affinity site” in the N-terminal part and a second one in the histidine-rich region, suggesting a double function for this protein in both nickel storage and CODH maturation. Further, RrCooJ undergoes a dynamical and reversible oligomerization process upon nickel exposure. Overall, these results bring the scientific knowledge a step forward towards the understanding of the CODH maturation pathway.

Keywords:
enzyme, dehydrogenase, monoxide

On-line thesis.