Enhancing Organophosphorus Hydrolase Stability by Immobilization on Chitosan Beads Containing Glutaraldehyde

Enhancing organophosphate hydrolase efficacy via protein engineering and immobilization strategies

Organophosphorus compounds (OPs), developed as pesticides and chemical warfare agents, are extremely toxic chemicals that pose a public health risk. Of the different detoxification strategies, organophosphate-hydrolyzing enzymes have attracted much attention, providing a potential route for detoxifying those exposed to OPs. Phosphotriesterase (PTE), also known as organophosphate hydrolase (OPH), is one such enzyme that has been extensively studied as a catalytic bioscavenger. In this review, we will discuss the protein engineering of PTE aimed toward improving the activity and stability of the enzyme. In order to make enzyme utilization in OP detoxification more favorable, enzyme immobilization provides an effective means to increase enzyme activity and stability. Here, we present several such strategies that enhance the storage and operational stability of PTE/OPH.

Novel approach using activated cellulose film for efficient immobilization of purified diamine oxidase to enhance enzyme performance and stability

The presence of various contaminants in foodstuffs has led to serious public health concerns. Diamine oxidase (DAO) has attracted tremendous attention for guarding food safety as well as clinical and environmental industries. In this study, DAO from Pisum sativum (Pea) seedlings was extracted and purified by dialysis and gel filtration. Purified DAO was covalently immobilized onto the surface of nitrocellulose membrane using glutaraldehyde. The obtained bioaffinity support has efficiently shown high yield immobilization of DAO from pea seedlings. The optimal conditions of free and immobilized DAO activity were evaluated against the substrate, Putrescine dihydrochloride. The influence of pH, temperature, storage stability, and reusability of immobilized enzyme with comparison to the free enzyme was studied and the results showed that the stabilities were significantly enhanced compared with free counterpart. Residual activity of the immobilized enzyme was 59% of the initial activity after being recycled 10 times. We approve that this novel low cost immobilized DAO carrier presents a new approach in large scale applications.

Engineering and introduction of de novo disulphide bridges in organophosphorus hydrolase enzyme for thermostability improvement

The organophosphorus hydrolase (OPH) has been used to degrade organophosphorus chemicals, as one of the most frequently used decontamination methods. Under chemical and thermal denaturing conditions, the enzyme has been shown to unfold. To utilize this enzyme in various applications, the thermal stability is of importance. The engineering of de novo disulphide bridges has been explored as a means to increase the thermal stability of enzymes in the rational method of protein engineering. In this study, Disulphide by Design software, homology modelling and molecular dynamics simulations were used to select appropriate amino acid pairs for the introduction of disulphide bridge to improve protein thermostability. The thermostability of the wild-type and three selected mutant enzymes were evaluated by half-life, delta G inactivation (ΔGi) and structural studies (fluorescence and far-UV CD analysis). Data analysis showed that half-life of A204C/T234C and T128C/E153C mutants were increased up to 4 and 24 min, respectively; however, for the G74C/A78C mutant, the half-life was decreased up to 9 min. For the T128C/E124C mutant, both thermal stability and Catalytic efficiency (kcat) were also increased. The half-life and ΔGi results were correlated to the obtained information from structural studies by circular dichroism (CD) spectrometry and extrinsic fluorescence experiments; as rigidity increased in A204C/T2234C and T128C/E153C mutants, half-life and ΔGi also increased. For G74C/A78C mutant, these parameters decreased due to its higher flexibility. The results were submitted a strong evidence for the possibility to improve the thermostability of OPH enzyme by introducing a disulphide bridge after bioinformatics design, even though this design would not be always successful.