Urease

What was reviewed?

This review comprehensively examines the enzyme urease, focusing on both its classical catalytic activity—urea hydrolysis into ammonia and carbamate—and its lesser-known non-enzymatic biological roles. Historically significant as the first enzyme ever crystallized and the first protein shown to require nickel as a cofactor, urease has since been implicated in a wide range of biological processes, spanning nitrogen metabolism, virulence in microbial pathogenesis, plant defense, neurotoxicity, and bioinsecticidal activity. The paper delves into the structural, kinetic, and molecular properties of ureases, including their activation mechanisms involving nickel insertion, their evolutionary divergence among taxa, and the role of accessory proteins (e.g., UreD, UreF, UreG, UreE) in catalytic site maturation. Importantly, the review explores biological functions of ureases unrelated to ureolytic activity, such as immunomodulation, platelet aggregation, neurotoxicity, and membrane-disruptive activities, often mediated by urease-derived peptides like jaburetox.

In addition, the review provides a detailed classification and discussion of urease inhibitors, such as hydroxamic acids, polyphenols, quinones, and heavy metals, many of which act through nickel chelation or active site disruption.

Who was reviewed?

This review encompasses a broad range of urease-producing organisms, including bacteria (e.g., Helicobacter pylori, Proteus mirabilis, Klebsiella pneumoniae, Cryptococcus neoformans), fungi, and plants (e.g., Canavalia ensiformis, Glycine max), with structural and functional insights derived from both natural and recombinant sources. The microbial taxa included are of special clinical interest due to their virulence mechanisms tied to urease activity or urease-derived functions. Data from both in vivo and in vitro experimental systems are integrated.

Most Important Findings

The review reveals that urease functions extend far beyond ammonia production via urea hydrolysis. Ureases are nickel-dependent metalloenzymes whose virulence-related capabilities involve both their enzymatic activity and structurally embedded, ureolysis-independent functions. These include pro-inflammatory signaling, platelet activation, immunomodulation, and neurotoxicity. Particularly in H. pylori, urease subunits (e.g., UreA and UreB) interact with host receptors such as CD74 to induce cytokine production (e.g., IL-8) and modulate immune responses. Insects and fungi are also affected by urease toxicity via peptides like jaburetox and soyuretox, which exhibit ion channel activity, membrane perturbation, and intracellular signaling effects. These activities are critical for the entomotoxic and antifungal properties observed in plant defense mechanisms.

From a microbiome standpoint, urease-positive pathogens are commonly enriched in dysbiotic states. Major pathogens with urease activity include H. pylori,P. mirabilis, K. pneumoniae, and C. neoformans, among others. Urease contributes to microbial survival in hostile pH environments, formation of urinary and gastric calculi, and systemic hyperammonemia, thereby modulating host-microbiota interactions in both the gut and urogenital tract. Notably, the review underscores the therapeutic potential of targeting urease pathways—including both enzymatic and structural features—for conditions such as hepatic encephalopathy, urinary tract infections, and H. pylori-associated diseases.

Greatest Implications

This review reframes urease as a multifunctional protein, positioning it as both a microbial virulence determinant and a target for pharmacological and agricultural interventions. Clinically, its role in pathogenesis via ammonia production and non-catalytic interactions implicates it in systemic diseases far beyond local infections, including cardiovascular and neurological disorders. For microbiome-targeted medicine, understanding urease as a functional trait rather than a taxonomic marker offers a mechanistic basis for identifying Major Microbial Associations (MMAs) and designing microbiome-targeted interventions (MBTIs), such as nickel chelators (lactoferrin, dimethylglyoxime (DMG), or a Low-Nickel Diet (LNiD). The dual catalytic and non-catalytic activities of urease also suggest the need for multi-modal inhibition strategies. In agriculture, urease-derived peptides could support biocontrol applications, while urease overexpression or peptide transgenesis could bolster crop resistance to pests and fungal pathogens.

What was studied?

This experimental study investigated the therapeutic potential of the nickel-specific chelator dimethylglyoxime (DMG) as an antimicrobial intervention against multidrug-resistant (MDR) enteric pathogens, specifically Salmonella enterica serovar Typhimurium and Klebsiella pneumoniae. The research assessed whether nickel chelation by DMG could inhibit the growth and virulence of these pathogens in vitro and in vivo through interference with essential Ni-dependent bacterial enzymes.

Who was studied?

The study utilized bacterial strains of MDR Klebsiella pneumoniae (ATCC BAA-2472) and MDR Salmonella Typhimurium (ATCC 700408 and ATCC 14028), in addition to two animal models: Mus musculus (mice) for assessing DMG efficacy and safety in systemic infection, and Galleria mellonella (wax moth larvae) for testing virulence attenuation in an invertebrate model.

What were the most important findings?

This study provides compelling evidence that dimethylglyoxime (DMG), a nickel-specific chelator, exerts a potent bacteriostatic effect against multidrug-resistant Salmonella Typhimurium and Klebsiella pneumoniae by inhibiting key Ni-dependent enzymes—hydrogenase and urease, respectively. At concentrations between 1 and 5 mM, DMG impaired enzyme activity without exhibiting toxicity in murine or invertebrate models. In vivo, DMG administration resulted in 50% survival among infected mice, compared to complete lethality in untreated controls, and led to a 10-fold reduction in bacterial colonization of the liver and spleen. In Galleria mellonella, pre-injection with DMG improved survival by 40–60% after challenge with lethal doses of MDR pathogens. NMR analysis confirmed DMG’s systemic absorption by detecting it in liver tissue. The absence of adverse effects in either model underscores the compound's therapeutic safety. The targeted suppression of nickel-requiring pathogens supports the utility of metallome-directed interventions in combating MDR infections, particularly for pathogens that rely on nickel-dependent enzymes for virulence.

What are the greatest implications of this study?

This study underscores the translational potential of metallome-targeted interventions, specifically through nickel chelation, as a viable therapeutic approach against MDR pathogens. By inhibiting bacterial nickel-dependent enzymatic machinery critical for virulence and survival, such as hydrogenases and ureases, DMG offers a mechanism-based strategy that bypasses conventional antibiotic resistance pathways. The fact that many high-priority MDR pathogens identified by the WHO possess Ni-dependent enzymes positions nickel chelation as a broadly applicable antimicrobial modality. Moreover, the non-toxic profile of DMG in two distinct animal models supports its development for clinical use, particularly as an adjunct or alternative to antibiotics in cases of resistant infections.