Urease is known to be a major contributor to pathologies induced by Helicobacter pylori and Proteus species. In H pylori , urease allows the bacteria to survive in an acidic gastric environment during colonisation, playing an important role in the pathogenesis of gastric and peptic ulcers. Ureolytic activity also results in the production of ammonia in close proximity to the gastric epithelium, causing cell damage and inflammation. In the case of Proteus species (notably Proteus mirabilis ) infection, stones are formed due to the presence of ammonia and carbon dioxide released by urease action. In addition, the ammonia released is able to damage the glycosaminoglycan layer, which protects the urothelial surface against bacterial infection. In this context, the administration of urease inhibitors may be an effective therapy for urease-dependent pathogenic bacteria. This is a review of the role of ureases in H pylori and Proteus species infections, focussing on the biochemical and clinical aspects of the most promising and/or potent urease inhibitors for the treatment of gastric and urinary tract infections.

Oxidative deamination of dopamine produces the highly toxic aldehyde 3,4-dihydroxyphenylacetaldehyde (DOPAL), enhanced production of which is found in post-mortem brains of Parkinson disease patients. When injected into the substantia nigra of rat brains, DOPAL causes the loss of dopaminergic neurons accompanied by the accumulation of potentially toxic oligomers of the presynaptic protein α-synuclein (aS), potentially explaining the synergistic toxicity described for dopamine metabolism and aS aggregation. In this work, we demonstrate that DOPAL interacts with aS via formation of Schiff-base and Michael-addition adducts with Lys residues, in addition to causing oxidation of Met residues to Met-sulfoxide. DOPAL modification leads to the formation of small aS oligomers that may be cross-linked by DOPAL. Both monomeric and oligomeric DOPAL adducts potently inhibit the formation of mature amyloid fibrils by unmodified aS. The binding of aS to either lipid vesicles or detergent micelles, which results in a gain of α-helix structure in its N-terminal lipid-binding domain, protects the protein against DOPAL adduct formation and, consequently, inhibits DOPAL-induced aS oligomerization. Functionally, aS-DOPAL monomer exhibits a reduced affinity for small unilamellar vesicles with lipid composition similar to synaptic vesicles, in addition to diminished membrane-induced α-helical content in comparison with the unmodified protein. These results suggest that DOPAL could compromise the functionality of aS, even in the absence of protein oligomerization, by affecting the interaction of aS with lipid membranes and hence its role in the regulation of synaptic vesicle traffic in neurons.

In this work we compared two plant ureases, jackbean urease (JBU) and embryo‐specific soybean urease (SBU) and a bacterial (Bacillus pasteurii) urease, for kinetic parameters and other biological properties described recently for ureases that are independent of the ureolytic activity. The insecticidal effect of ureases was investigated in feeding trials with the cotton sucker bug, Dysdercus peruvianus (Hemiptera) as an insect model. Contrasting with B. pasteurii urease (PBU), both plant ureases presented potent insecticidal activity, with LD₅₀ values of 0.017% (w/w) and 0.052% (w/w) for JBU and SBU, respectively. The insecticidal property of JBU or SBU was not affected by treatment with p‐hydroxymercuribenzoate, an irreversible inhibitor of ureolytic activity of both proteins. Also, contrasting with canatoxin – a urease isoform from jackbean seeds that displays a toxic effect in mice (LD₅₀ = 2 mg·kg⁻¹) – no lethality was seen in mice injected intraperitoneally with JBU or SBU (20 mg·kg⁻¹). Similarly to canatoxin, the three enzymes promoted aggregation of blood platelets (EC₅₀ = 400.0 µg·mL⁻¹, 22.2 µg·mL⁻¹, 15.8 µg·mL⁻¹ for BPU, SBU and JBU, respectively). This platelet activating property was also independent of urease activity. Comparison of the kinetic properties indicated that SBU is fivefold less susceptible than JBU to inhibition by acetohydroxamic acid, a chelator of Ni⁺² and Zn⁺² ions. The ureases also showed different susceptibility to agents that modify cysteine residues, such as p‐hydroxymercuribenzoate and p‐benzoquinone. Altogether, these data emphasize that biological properties that are independent of ureolytic activity are not restricted to jackbean ureases and that these proteins may have a role in plant defense against insect predators.

Fibrillization of the protein α‐synuclein (α‐syn) is a hallmark of Parkinson's disease and other α‐synucleinopathies. The well‐established idea that α‐syn is a natively disordered monomer prone to forming fibrils was recently challenged by data showing that the protein mostly exists in vitro and in vivo as helically folded tetramers that are resistant to fibrillization. These apparently conflicting findings may be reconciled by the idea that α‐syn exists as a disordered monomer in equilibrium with variable amounts of dynamic oligomeric species. In this context, varying the approaches used for protein purification, such as the method used to lyse cells or the inclusion of denaturing agents, could dramatically perturb this equilibrium and hence alter the relative abundance of the disordered monomer. In the present study, we investigated how the current methods for α‐syn purification affect the structure and oligomeric state of the protein, and we discuss the main pitfalls associated with the production of recombinant α‐syn in Escherichia coli. We demonstrate that α‐syn was expressed in E. coli as a disordered monomer independent of both the cell lysis method and the use of heating/acidification for protein purification. In addition, we provide convincing evidence that the disordered monomer exists in equilibrium with a dynamic dimer, which is not an artefact of the cross‐linking protocol as previously suggested. Unlike the helically folded tetramer, α‐syn dimer is prone to fibrillate and thus it may be an interesting target for anti‐fibrillogenic molecules.Structured digital aplha-Syn and aplha-Syn bind by cross-linking study (View interaction) aplha-Syn and aplha-Syn bind by detection by mass spectrometry (1, 2) aplha-Syn and aplha-Syn bind by molecular sieving (View interaction) aplha-Syn and aplha-Syn bind by circular dichroism (View interaction)