A Solvent‐Exposed Cysteine Forms a Peculiar Ni II ‐Binding Site in the Metallochaperone CooT from Rhodospirillum rubrum

Rational Development of Bacterial Ureases Inhibitors

Urease, an enzyme that catalyzes the hydrolysis of urea, is a virulence factor of various pathogenic bacteria. In particular, Helicobacter pylori, that colonizes the digestive tract and Proteus spp., that can infect the urinary tract, are related to urease activity. Therefore, urease inhibitors are considered as potential therapeutics against these infections. This review describes current knowledge of the structures, activity, and biological importance of bacterial ureases. Moreover, the structure-based design of several classes of bacterial urease inhibitors is presented and discussed. Phosphinic and phosphonic acids were applied as transition-state analogues, while Michael acceptors and ebselen derivatives were applied as covalent binders of cysteine residue. This review incorporates bacterial urease inhibitors from literature published between 2008 and 2021.

Kinetic and structural analysis of the inactivation of urease by mixed-ligand phosphine halide Ag(I) complexes

Soft metal ions can inactivate urease, a Ni(II)-dependent enzyme whose hydrolytic activity has significant implications in agro-environmental science and human health. Kinetic and structural studies of the reaction of Canavalia ensiformis urease (JBU) and Sporosarcina pasteurii urease (SPU) with Ag(I) compounds of general formula [Ag(PEt₃)X]₄ (X = Cl, Br, I), and with the ionic species [Ag(PEt₃)₂]NO₃, revealed the role of the Ag(I) ion and its ligands in modulating the metal-enzyme interaction. The activity of JBU is obliterated by the [Ag(PEt₃)X]₄ complexes, with IC₅₀ values in the nanomolar range; the efficiency of the inhibition increases in the Cl^- < Br^- < I^- order. The activity of JBU upon [Ag(PEt₃)₂]NO₃ addition decreases to a plateau corresponding to ca. 60% of the original activity and decreases with time at a reduced rate. Synchrotron X-ray crystallography on single crystals obtained after the incubation of SPU with the Ag(I) complexes yielded high-resolution (1.63-1.97 Å) structures. The metal-protein adducts entail a dinuclear Ag(I) cluster bound to the conserved residues αCys322, αHis323, and αMet367, with a bridging cysteine thiolate atom, a weak Ag^…Ag bond, and a quasi-linear Ag(I) coordination geometry. These observations suggest a mechanism that involves the initial substitution of the phosphine ligand, followed by a structural rearrangement to yield the dinuclear Ag(I) cluster. These findings indicate that urease, in addition to the active site dinuclear Ni(II) cluster, possesses a secondary metal binding site, located on the mobile flap domain, capable of recognizing pairs of soft metal ions and controlling catalysis.

The structure-based reaction mechanism of urease, a nickel dependent enzyme: tale of a long debate

This review is an attempt to retrace the chronicle that starts from the discovery of the role of nickel as the essential metal ion in urease for the enzymatic catalysis of urea, a key step in the biogeochemical cycle of nitrogen on Earth, to the most recent progress in understanding the chemistry of this historical enzyme. Data and facts are presented through the magnifying lenses of the authors, using their best judgment to filter and elaborate on the many facets of the research carried out on this metalloenzyme over the years. The tale is divided in chapters that discuss and describe the results obtained in the subsequent leaps in the knowledge that led from the discovery of a biological role for Ni to the most recent advancements in the comprehension of the relationship between the structure and function of urease. This review is intended not only to focus on the bioinorganic chemistry of this beautiful metal-based catalysis, but also, and maybe primarily, to evoke inspiration and motivation to further explore the realm of bio-based coordination chemistry.

Structure, function, and biosynthesis of nickel-dependent enzymes

Nickel enzymes, present in archaea, bacteria, plants, and primitive eukaryotes are divided into redox and nonredox enzymes and play key functions in diverse metabolic processes, such as energy metabolism and virulence. They catalyze various reactions by using active sites of diverse complexities, such as mononuclear nickel in Ni-superoxide dismutase, glyoxylase I and acireductone dioxygenase, dinuclear nickel in urease, heteronuclear metalloclusters in [NiFe]-carbon monoxide dehydrogenase, acetyl-CoA decarbonylase/synthase and [NiFe]-hydrogenase, and even more complex cofactors in methyl-CoM reductase and lactate racemase. The presence of metalloenzymes in a cell necessitates a tight regulation of metal homeostasis, in order to maintain the appropriate intracellular concentration of nickel while avoiding its toxicity. As well, the biosynthesis and insertion of nickel active sites often require specific and elaborated maturation pathways, allowing the correct metal to be delivered and incorporated into the target enzyme. In this review, the phylogenetic distribution of nickel enzymes will be briefly described. Their tridimensional structures as well as the complexity of their active sites will be discussed. In view of the latest findings on these enzymes, a special focus will be put on the biosynthesis of their active sites and nickel activation of apo-enzymes.