Heterologous expression of recombinant urate oxidase using the intein-mediated protein purification in Pichia pastoris

The potential of urate oxidase (uricase) for clinical use has been highlighted because of its role in lowering the blood uric acid levels for the treatment of tumor lysis syndrome. In the present study, the codon-optimized synthetic gene of Aspergillus flavus uricase was fused to the Mxe GyrA intein and chitin-binding domain. The construct was inserted into pPICZA and pPICZαA vectors and electroporated into Pichia pastoris GS115 for the cytosolic and secretory expression. Transformants were screened on gradients of Zeocin up to 2000 μg/ml to find multi-copy integrants. For both constructs, colonies with more resistance were screened for the highest uricase producers by enzyme assay. PCR analysis confirmed successful cassettes insertion into the genome and Mut + phenotype. The gene copy index was determined to be two and five for cytosolic and secretory strains, respectively. Productivity of the cytosolic and secretory strains was found to be 0.74 and 0.001 U/ml culture media in order while the cytosolic recombinant enzyme accounted for about 6% of total proteins. One-step purification of the expressed uricase was done with the aid of the chitin affinity column, followed by DTT induction for intein on-column cleavage. The yield of 40.8 mg/L and K m of 0.22 mM was obtained for intracellular expression. It seems that the intracellular production of uricase can indeed serve as an effective alternative to secretory expression. Moreover, this is the first report considering cytosolic production of uricase using the intein-mediated protein purification in the methylotrophic yeast, P. pastoris.

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.