Inducible expression of a β-glucuronidase from Penicillium purpurogenum in Pichia pastoris and characterization of the recombinant enzyme

The present study reports the recombinant expression and partial characterization of a novel β-glucuronidase gene from Penicillium purpurogenum Li-3. It is the first time that a β-glucuronidase gene was cloned from Penicillium purpurogenum (pgus, Genbank Accession NO. EU095019). Sequence analysis indicated that pgus has 1815 base pairs, encoding 604 amino acids with the potential molecular weight of 66.7 kDa and 4 potential N-glycosylation sites. The pgus gene was successfully expressed as a functional protein (PGUS-P) in Pichia pastoris GS115. The optimal reaction temperature and pH of PGUS-P were 37.5 °C and pH5.2, respectively. While higher thermal and pH stability were observed in PGUS-P. The Km and Vmax values of PGUS-P for glycyrrhizin ammonium salt (GL) were 0.48 mM and 0.133 mM/min, respectively. The research also showed that the Mg²⁺, Mn²⁺ and Na⁺ have activation effect, while Ag⁺ and SDS has inhibition effect on the activity of catalyst. In addition, the mature PGUS-P protein exhibited a molecular mass of approximately 90 kDa on SDS-PAGE, which is much higher than its theoretical value. The results revealed that the recombinant PGUS-P may be partly N-glycosylated.