Characterization and Cys-directed mutagenesis of urate oxidase from Bacillus subtilis BS04

Isolation and Characterization of Highly Active Uricase from Alcaligenes spp. Strain UR1

For the first time, this study reports extracellular uricase enzyme isolation and characterization from strain UR1 of Alcaligenes spp. from Western Saudi Arabia. The strain efficiently produced highly active extracellular uricase for therapeutic applications. It offers a simplified enzyme purification approach rather than complicated intracellular enzyme purification from other microbes. Strain UR1 exhibited significantly higher uricase synthesis potential [916 U/mg (specific activities) and 275 U/ml (volume)]. The study optimized the conditions (37°C and pH 7.4) for 10% enhanced uricase production in the BT medium where sucrose served as the carbon source. Uricase enzyme remained stable at various pH levels (5-9) up to 50°C, however, the optimal activity was noted at 40°C and pH 7.5. The strain was sensitive to EDTA-like inhibitors. Ca2+ improved the strain activity, which could yield potent formulations for clinical and industrial applications. This novel aspect presents Alcaligenes spp. strain UR1 as a promising candidate for the treatment of hyperuricemia and gout. It offers an efficient and inexpensive alternative for uricase synthesis at the industrial scale. These findings encourage further investigations regarding genetic aspects of uricase for improved bioprocessing and therapeutic applications.

High yield expression and purification of Aspergillus flavus uricase cloned in Pichia pink™ expression system

In this research, for the first time, A. flavus uricase gene was cloned in pPink-UOX plasmid under strong alcohol oxidase promoter of Pichia pink expression system after codon optimization. After selecting the best uricase producing clone with an activity of 0.7 U/ml at the Flask level, a 5-L fermenter was used to increase the expression of the enzyme. Within 60 h, the fermentation process produced 1500 g of biomass from 4 L of semi defined culture media and expressed 2.5 g/L of the enzyme. The purity of recombinant uricase production using three consecutive DEAE Sepharose, CM Sepharose and Phenyl Sepharose columns was above 99%, which was confirmed by SDS-PAGE and RP-HPLC analyses. Size exclusion chromatography analysis showed that the purified enzyme has comparable heterogeneity to the Rasburicase. The yield of recombinant uricase production in this study was 63% and its specific activity was 24 U/mg. The high expression of recombinant uricase in the Pichia pink strain and the increased enzyme activity compared to the standard sample indicate the potential of therapeutic and diagnostic applications of recombinant uricase in the present study.

The effects of free Cys residues on the structure, activity, and tetrameric stability of mammalian uricase

Mammalian uricases contain four conserved cysteine (Cys) residues, but little is known about their structures and functions. In this study, we first confirmed that all four Cys residues are free and not involved in disulfide bond formation, using canine uricase as a model protein. Cys residues had a greater effect on stability than on activity based on single Cys-to-Ser (serine) substitutions. Circular dichroism (CD) and homology modeling indicated that C188S reduces β-sheet contents and inter- and intra-subunit hydrophobic interaction, potentially impairing the core tetrameric β-barrel structure of the tunneling-fold protein, and ultimately decreased the tetrameric stability. Additionally, the inactivation of C188S during the stability tests may be a complex process involving depolymerization followed by irregular aggregation. Double mutations or thiol blockage of Cys188 and Cys195 significantly disrupted the formation and stability of tetrameric uricase, which may be mediated by the free thiols in Cys residues. The present results demonstrated that the free Cys residues are essential for tetrameric formation and stability in mammalian uricase. This implies that free cysteine residues, although not involved in disulfide bonding, may play important structural roles in certain proteins, underscoring the significance of the hydrophobic characteristics of the free thiols in Cys residues. KEY POINTS: • Four Cys residues are not involved in disulfide bonding in mammalian uricase. • The hydrophobicity of free thiols is critical for tetrameric stability in uricase. • Free Cys residues can serve structural roles without involving in disulfide bonds.

Characterization of a novel marine microbial uricase from Priestia flexa and evaluation of the effects of CMCS conjugation on its enzymatic properties

A novel uricase producing marine bacterium Priestia flexa alkaAU was isolated and identified. The 16S rDNA and the uricase coding gene were sequenced, analyzed and submitted to GenBank. The uricase from Priestia flexa alkaAU (PFU) was purified, determined to be 58.87 kDa, and conjugated with carboxymethyl chitosan (CMCS) by ionic gelation. CMCS conjugation had no effect on the optimum pH of PFU but decreased the optimum temperature by 10 °C. CMCS conjugation increased the specific activity of PFU by 53% at the human body temperature (37 °C) and small intestine's pH (pH 6.8). Uricase thermostabilizing ability of CMCS was significant in the range of 37-80 °C but not at lower temperatures. For improvement of the pH stability of PFU, CMCS was more effective at pHs 3-5 than pHs 6-11. CMCS increased the half-life of PFU against artificial intestinal fluid by 1.5 folds, which demonstrated the potential capability of CMCS-PFU for oral administration.