Looking into a highly thermostable and efficient recombinant manganese-catalase from Geobacillusthermopakistaniensis

Differential Impact of Zinc Salt Precursors on Physiognomies, Anticancerous, and Antibacterial Activities of Zinc Oxide Nanoparticles

Zinc oxide nanoparticles (ZnONPs) are enormously popular semi-conductor metal oxides with diverse applications in every field of science. Many physical and chemical methods applied for the synthesis of ZnONPs are being rejected due to their environmental hazards. Therefore, ZnONPs synthesized from plant extracts are steered as eco-friendly showing more biocompatibility and biodegradability. Additionally, various synthesis conditions such as the type of precursor salt also play a role in influencing the physicochemical and biological properties of ZnONPs. In this study, green synthesis of ZnONPs from Acacia nilotica was carried out using zinc acetate (ZA-AN-ZNPs), zinc nitrate (ZN-AN-ZNPs), and zinc sulfate (ZS-AN-ZNPs) precursor salts. Surprisingly, characterization of ZnONPs using UV-visible spectroscopy, TEM, XRD, and EDX revealed the important role precursor salts played in influencing the size and shape of ZnONPs, i.e., 20-23 nm spherical (ZA-AN-ZNPs), 55-59 nm triangular (ZN-AN-ZNPs), and 94-97 nm nano-flowers (ZS-AN-ZNPs). FTIR analysis showed the involvement of alkaloids, alcohols, carboxylic acid, and phenolic compounds present in Acacia nilotica extract during the synthesis process. Since different precursor salts showed different morphology of ZnONPs, their biological activities were also variable. ZN-AN-ZNPs showed the highest cytotoxicity towards HepG2 cells with the lowest cell viability (28.92 ± 0.99%), highest ROS/RNS production (3425.3 ± 184.58 relative DHR123 fluorescence), and loss of mitochondrial membrane potential (1645.2 ± 32.12 relative fluorescence unit) as well as induced significant caspase-3 gene expression. In addition to this, studying the zone of inhibitions and minimum bactericidal and inhibitory concentrations of ZnONPs showed their exceptional potential as antibacterial agents. At MIC as low as 8 µg/mL, ZA-AN-ZNPs and ZN-AN-ZNPs exhibited significant bactericidal activities against human pathogens Klebsiella pneumoniae and Listeria monocytogenes, respectively. Furthermore, alkaline phosphatase, DNA/RNA leakage, and phosphate ion leakage studies revealed that a damage to the bacterial cell membrane and cell wall is involved in mediating the antibacterial effects of ZnONPs.

Role of C-terminal domain in a manganese-catalase from Geobacillus thermopakistaniensis

Catalases catalyze the decomposition of hydrogen peroxide into water and oxygen. We have characterized two manganese-catalases from Geobacillus thermopakistaniensis, Cat_Gt and Cat-II_Gt, which exhibited significant variation in their sequence, structure and properties. There was only 23% sequence identity between the two. The striking structural difference was the presence of an extended C-terminal domain in Cat_Gt. Molecular modelling and docking studies revealed that deletion of the C-terminal domain removes non-specific binding, which results in increased substrate affinity. To verify experimentally, a C-terminal truncated version of Cat_Gt, named as Cat_Gt-ΔC, was produced in Escherichia coli and effects of deletion were analyzed. There was no significant difference in optimal pH, optimal temperature and substrate specificity of Cat_Gt and Cat_Gt-ΔC. However, K_m value was reduced from 259 to 157 mM and Cat_Gt-ΔC exhibited ∼1.5-fold higher catalytic efficiency as compared to Cat_Gt. Furthermore, removal of the C-terminal domain converted the tetrameric nature to monomeric, and reduced the thermostability of the truncated protein. These results demonstrate that C-terminal domain of Cat_Gt might have little role in maintaining enzyme function but provides additional structural stability to the protein, which is a desired property for industrial applications.