Recombinant production of Aspergillus Flavus uricase and investigation of its thermal stability in the presence of raffinose and lactose

The role of Gln269Leu mutation on the thermostability and structure of uricase from Aspergillus flavus

Aspergillus flavus Urate oxidase (AFUOX) is promising for potential therapeutic applications, particularly in gout treatment. However, the enzyme's low thermostability and solubility limit its efficacy. A targeted mutation, substituting Gln with Leu at position 269 (Q269L) has been proposed to enhance its stability. The turnover number, catalytic efficiency, and specific activity of Q269L were 3.7 (s-1), 53.2 (mM-1. s-1), and 3.926 U/mg, respectively. In comparison, for the wild type, these were 3.1 (S-1), 35.1 (mM-1. s-1), and 4.018 U/mg, respectively. Notably, the wild type exhibited maximum activity at pH 9 and 25 °C, whereas the activity of Q269L was obtained at pH 9.5 and 30 °C. Furthermore, the half-life of Q269L at 40 °C is significantly longer (85.55 min) compared to the wild-type (49.85 min). The thermodynamic parameters ΔH≠, ΔS≠, and ΔG≠ at 40 °C for Q269L were 60.9 kJ.mol-1, -276 J.mol-1, and 147.3 kJ.mol-1, respectively. Intrinsic fluorescence reductions and ANS fluorescence increases suggest that tryptophan resides in a polar environment with augmented hydrophobic pockets. FTIR analysis of Q269L reveals a decrease in β-sheet and an increase in α-helix structures, supporting molecular dynamics simulations. Collectively, MD and experimental results underscore Q269L's enhanced thermostability and localized structural alterations, advancing AFUOX's therapeutic potential.

Maximization of uricase production in a column bioreactor through response surface methodology-based optimization

Uricase (EC 1.7.3.3) is an oxidoreductase enzyme that is widely exploited for diagnostic and treatment purposes in medicine. This study focuses on producing recombinant uricase fromE. coliBL21 in a bubble column bioreactor (BCB) and finding the optimal conditions for maximum uricase activity. The three most effective variables on uricase activity were selected through the Plackett-Burman design from eight different variables and were further optimized by the central composite design of the response surface methodology (RSM). The selected variables included the inoculum size (%v/v), isopropylβ-d-1-thiogalactopyranoside (IPTG) concentration (mM) and the initial pH of the culture medium. The activity of uricase, the final optical density at 600 nm wavelength (OD600) and the final pH were considered as the responses of this optimization and were modeled. As a result, activity of 5.84 U·ml-1and a final OD600of 3.42 were obtained at optimum conditions of 3% v/v inoculum size, an IPTG concentration of 0.54 mM and a pH of 6.0. By purifying the obtained enzyme using a Ni-NTA agarose affinity chromatography column, 165 ± 1.5 mg uricase was obtained from a 600 ml cell culture. The results of this study show that BCBs can be a highly effective option for large-scale uricase production.

Recombinant Expression and Functional Assessment of Uricase from a Pertinent Origin of the Enzyme, Streptomyces sp. Strain 17-1

Background

Uricase or urate oxidase, as a therapeutic enzyme, is extensively applied to oxidize accumulated uric acid in the body to soluble form to treat related illnesses.

Objectives

This study was conducted with the aim of searching for potential sources of uricase-producing Streptomyces from Eshtehard salt desert in Alborz province, Iran and heterologous expression, purification and functional assay of the enzyme.

Materials and Methods

Main screening was conducted by cultivation of the strains on a medium enriched with 0.3 percent (w/v) uric acid. The uricase gene from the most potent strain was then recombinantly expressed in E. coli BL21 (DL3).

Results

Out of the tested strains, only seven showed uricase activity. The highest level of native uricase activity (11.5735 U.mL-1) belonged to strain 17-1, which had the closest similarity to Streptomyces nigra. A recombinant uricase with a molecular mass of approximately 38 kDa was produced. The purified uricase exhibited a specific activity of about 28.29±0.59 U.mg-1, which is among the highest level of uricase activity reported by other studies.

Conclusions

This enzyme is a promising candidate for further applicable investigations and large-scale production in terms of its large volume of soluble expression and selective competitive activity.

Enhancement of Thermostability of Aspergillus flavus Urate Oxidase by Immobilization on the Ni-Based Magnetic Metal-Organic Framework

The improvement in the enzyme activity of Aspergillus flavus urate oxidase (Uox) was attained by immobilizing it on the surface of a Ni-based magnetic metal–organic framework (NimMOF) nanomaterial; physicochemical properties of NimMOF and its application as an enzyme stabilizing support were evaluated, which revealed a significant improvement in its stability upon immobilization on NimMOF (Uox@NimMOF). It was affirmed that while the free Uox enzyme lost almost all of its activity at ~40–45 °C, the immobilized Uox@NimMOF retained around 60% of its original activity, even retaining significant activity at 70 °C. The activation energy (Ea) of the enzyme was calculated to be ~58.81 kJ mol⁻¹ after stabilization, which is approximately half of the naked Uox enzyme. Furthermore, the external spectroscopy showed that the MOF nanomaterials can be coated by hydrophobic areas of the Uox enzyme, and the immobilized enzyme was active over a broad range of pH and temperatures, which bodes well for the thermal and long-term stability of the immobilized Uox on NimMOF.

Molecular Elucidation of a Urate Oxidase from Deinococcus radiodurans for Hyperuricemia and Gout Therapy

Urate oxidase initiates the uric acid degradation pathways and is extensively used for protein drug development for gout therapy and serum uric acid diagnosis. We first present the biochemical and structural elucidation of a urate oxidase from the extremophile microorganism Deinococcus radiodurans (DrUox). From enzyme characterization, DrUox showed optimal catalytic ability at 30 °C and pH 9.0 with high stability under physiological conditions. Only the Mg²⁺ ion moderately elevated its activity, which indicates the characteristic of the cofactor-free urate oxidase family. Of note, DrUox is thermostable in mesophilic conditions. It retains almost 100% activity when incubated at 25 °C and 37 °C for 24 h. In this study, we characterized a thermostable urate oxidase, DrUox with high catalytic efficiency and thermal stability, which strengthens its potential for medical applications.

New insight into the molecular mechanism of the trehalose effect on urate oxidase stability

Urate oxidase (EC 1.7.3.3) is a key enzyme in the purine metabolism which is applied in the treatment of gout and also, as a diagnostic reagent for uric acid detection. In the current study, the trehalose (TRE) effects as an additive on the structural stability and function of uricase were investigated. For recombinant expression of UOX in E. coli BL21 cells, firstly the coding sequence was subcloned into the pET-28a vector and after induction with IPTG, the recombinant UOX was purified by affinity chromatography using a Ni-NTA agarose column. To specify the trehalose effects on the urate oxidase (UOX) structure, optimum pH, optimum temperature, kinetic and thermodynamic parameters and also, the intrinsic fluorescence of UOX in the absence and presence of trehalose were examined. The UOX half-life is 24.32 min at 40 °C, whereas the UOX-TRE has a higher half-life (32.09 min) at this temperature. Generally, our findings confirm that trehalose has a protective effect on the enzyme structure. Optimum pH and temperature were 9 and 25 °C, respectively for both the naked and treated enzymes and their activity retained 42.18 and 64.80%, respectively after 48 h of incubation at room temperature. Also, theoretical results indicate that the random coil of the enzyme was converted to α-helix and β-sheet in the presence of trehalose which may preserve the integrity of the active site of the enzyme and increased the enzymatic activity. The MD simulation results indicated greater stability of the uricase structure in the presence of trehalose.Communicated by Ramaswamy H. Sarma.

Enhancement of Pharmaceutical Urate Oxidase Thermostability by Rational Design of De Novo Disulfide Bridge

Background and Purpose

As a therapeutic enzyme, urate oxidase is utilized in the reduction of uric acid in various conditions such as gout or tumor syndrome lysis. However, even bearing kinetical advantage over other counterparts, it suffers from structural instability most likely due to its subcellular and fungal origin.

Objectives

In this research, by using rational design and introduction of de novo disulfide bridge in urate oxidase structure, we designed and created a thermostable urate oxidase for the first time.

Materials and Methods

Utilizing site-directed mutagenesis and only with one point mutation we constructed two separate mutants: Ala6Cys and Ser282Cys which covalently linked subunits of enzyme each other. Single mutation to cysteine created three inter-chain disulfide bridges and one hydrogen bond in Ala6Cys and two disulfide bridges in Ser282Cys.

Results

Both mutants showed 10 °C increase in optimum activity compared to wild-type enzyme while the K_m values for both increased by 50% and their specific activity compromised. The thermal stability of Ser282Cys increased remarkably by comparing Ala6Cys and wild-type enzymes. Estimation of half life for wild-type enzyme demonstrated 38.5 min, while for Ala6Cys and Ser282Cys were 138 and 115 min, respectively. Interestingly, the optimal pH of both mutants was broaden from 7 to 10, which could make them candidates for industrial applications.

Conclusion

It seemed that introducing disulfide bridges resulted in local and overall rigidity by bringing two adjacent sites of enzyme together and decreasing the conformational entropy of unfolding state is responsible for the enhancement of thermostability.

Efficient purification of a recombinant tag-free thermostable Kluyveromyces marxianus uricase by pH-induced self-cleavage of intein and expression in Escherichia coli

Uricase as an important healthcare-related protein is extensively used in the treatment of tumor lysis syndrome and in the manufacture of serum uric-acid diagnostic kits. In this study, a gene of a new thermostable uricase (KmUOX) was cloned from thermotolerant yeast Kluyveromyces marxianus. The uricase was fused with a self-cleaving intein and cellulose-binding affinity tag and expressed in Escherichia coli BL21 (DE3). Through the binding to inexpensive cellulose and in situ intein cleavage induced by a pH change, tag-free uricase (KmUOX) was efficiently purified with a 77.11% yield via a single-step column purification strategy. This tag-free uricase showed K_m, V_max, and K_cat values of 67.60 µM, 56.35 µM/(min mg), and 32.74 S^-1, respectively. Furthermore, this pure uricase was relatively thermostable and retained 79.75% of activity when incubated at 40 °C for 90 h. Thus, this pH-induced self-cleavable intein system combined with a cellulose matrix for affinity chromatography is proven here to be an effective and low-cost method for recombinant-uricase purification. Moreover, the stability of KmUOX makes it useful for clinical applications.