Spectroscopic investigation of conformational changes in urease caused by interaction with humic acid

Synergistic mechanisms of humic acid and biomineralization in cadmium remediation using Lysinibacillus fusiformis

Heavy metal pollution, particularly cadmium, poses severe environmental and health risks due to its high toxicity and mobility, necessitating effective remediation strategies. While both microbially induced carbonate precipitation (MICP) and humic acid adsorption are promising methods for heavy metal mitigation, their combined effects, particularly the influence of humic acid on the MICP process, have not been thoroughly investigated. This study explores the interaction between humic acid and MICP, revealing that humic acid significantly inhibits the MICP process by reducing urease activity, with the 10% humic acid treatment resulting in a 23.8% reduction in urease activity compared to the control. Additionally, while higher concentrations of humic acid did not significantly reduce cadmium ion concentrations, they did result in a slight increase in organically bound cadmium, indicating an interaction that could alter metal speciation in the soil. These findings provide important insights into the mechanisms by which humic acid affects MICP, offering a foundation for optimizing combined remediation approaches. Future research should aim to fine-tune the balance between MICP and humic acid to enhance the overall efficiency of cadmium remediation strategies. This study contributes to the development of more effective and sustainable methods for addressing cadmium contamination.

Chlorogenic acid, caffeic acid and luteolin from dandelion as urease inhibitors: insights into the molecular interactions and inhibition mechanism

BACKGROUND

Dandelion contains hundreds of active compounds capable of inhibiting urease activity, but the individual compounds have not yet been fully identified, and their effects and underlying mechanisms are not clear. The present study aimed to screen the urease inhibition active compounds of dandelion by urease inhibitory activity evaluation HPLC-tandem mass spectrometry analysis, their mechanism of urease inhibition by polyphenols was explored using enzyme kinetic studies via Lineweaver-Burk plots. Other investigations included isothermal titration calorimetry and surface plasmon resonance sensing, fluorescence quenching experiments, and single ligand molecular docking and two-ligand simultaneous docking techniques.

RESULTS

The results indicated that the ethyl acetate fraction of dandelion flower exhibited the greatest inhibition (lowest IC50 0.184 ± 0.007 mg mL-1). Chlorogenic acid, caffeic acid and luteolin could be effective urease inhibitors that acted in a non-competitive inhibition manner. Individually, chlorogenic acid could not only fast bind to urease, but also dissociate rapidly, whereas luteolin might interact with urease with the weakest affinity. The chlorogenic acid-caffeic acid combination exhibited an additive effect in urease inhibition. However, the chlorogenic acid-luteolin and caffeic acid-luteolin combinations exhibited antagonistic effects, with the caffeic acid-luteolin combination showing greater antagonism.

CONCLUSION

The present study reveals that chlorogenic acid, caffeic acid and luteolin are major bioactive compounds for urease inhibition, indicating the molecular mechanisms. The antagonistic effects were observed between luteolin and chlorogenic acid/caffeic acid, and the interactions of the catalytic site and flap may account for the antagonistic effects. © 2024 Society of Chemical Industry.

Synergizing structure and function: Cinnamoyl hydroxamic acids as potent urease inhibitors

The current investigation encompasses the structural planning, synthesis, and evaluation of the urease inhibitory activity of a series of molecular hybrids of hydroxamic acids and Michael acceptors, delineated from the structure of cinnamic acids. The synthesized compounds exhibited potent urease inhibitory effects, with IC50 values ranging from 3.8 to 12.8 µM. Kinetic experiments unveiled that the majority of the synthesized hybrids display characteristics of mixed inhibitors. Generally, derivatives containing electron-withdrawing groups on the aromatic ring demonstrate heightened activity, indicating that the increased electrophilicity of the beta carbon in the Michael Acceptor moiety positively influences the antiureolytic properties of this compounds class. Biophysical and theoretical investigations further corroborated the findings obtained from kinetic assays. These studies suggest that the hydroxamic acid core interacts with the urease active site, while the Michael acceptor moiety binds to one or more allosteric sites adjacent to the active site.

Influence of humic acid on microbial induced carbonate precipitation for organic soil improvement

Microbial induced carbonate precipitation (MICP) is one of the most commonly researched topics on biocementation, which achieves cementation of soil particles by carbonate from urea hydrolysis catalyzed by microbial urease. Although most MICP studies are limited to stabilizing sandy soils, more researchers are now turning their interest to other weak soils, particularly organic soils. To stabilize organic soils, the influence of humic substances should be investigated since it has been reported to inhibit urease activity and disrupt the formation of calcium carbonate. This study investigates the effect of humic acid (HA), one fraction of humic substances, on MICP. For this purpose, the effects of HA content on CaCO₃ precipitation using three strains and on CaCO₃ morphology were examined. The results showed that native species in organic soils were less adversely affected by HA addition than the exogenous one. Another interesting finding is that bacteria seem to have strategies to cope with harsh conditions with HA. Observation of CaCO₃ morphology revealed that the crystallization process was hindered by HA to some extent, producing lots of fine amorphous precipitates and large aggregated CaCO₃. Overall, this study could provide an insightful understanding of possible obstacles when using MICP to stabilize organic soils.