Nickel-Induced Oligomerization of the Histidine-Rich Metallochaperone CooJ from Rhodospirillum Rubrum

[NiFe]-carbon monoxide dehydrogenase reversibly catalyzes the oxidation of CO to CO2. Its active site is a unique NiFe4S4 cluster, known as C-cluster. In Rhodospirillum rubrum, three nickel-dependent proteins, CooC, CooT and CooJ are required for Ni insertion into the active site. Among them, CooJ is a histidine-rich protein, containing two distinct and spatially separated Ni(II)-binding sites: a strictly conserved N-terminal site and a variable histidine tail at the C-terminus. Here, using biophysical techniques, we study the behavior of the protein upon Ni(II) addition. Using circular dichroism and chemical denaturation, we show that the binding of Ni(II) to the protein increases its stability. Moreover, high-order oligomers are formed through nickel–histidine tail interactions, both in vitro and in cellulo, via a dynamical and reversible process.