Shu-Ping Zou

N-glycosylation enhances functional and structural stability of recombinant β-glucuronidase expressed in Pichia pastoris

Recombinant β-glucuronidase (GUS) expressed in Pichia pastoris GS115 is an important glycoprotein, encoded by a gene with four potential N-glycosylation sites. To investigate the impact of N-linked carbohydrate moieties on the stability of recombinant GUS, it was deglycosylated by peptide-N-glycosidase F (PNGase-F) under native conditions. The enzymatic activities of the glycosylated and deglycosylated GUS were compared under various conditions such as temperature, pH, organic solvents, detergents and chaotropic agent. The results demonstrated that the glycosylated GUS retained greater fraction of maximum enzymatic activity against various types of denaturants compared with the deglycosylated. The conformational stabilities of both GUS were analyzed by monitoring the unfolding equilibrium by using the denaturant guanidinium chloride (dn-HCl). The glycosylated GUS displayed a significant increase in its conformational stability than the deglycosylated counterpart. These results affirmed the key role of N-glycosylation on the structural and functional stability of β-glucuronidase and could have potential applications in the functional enhancement of industrial enzymes.

N-linked glycosylation influences on the catalytic and biochemical properties of Penicillium purpurogenum β-d-glucuronidase

To study the influence of N-linked carbohydrate moiety on the catalytic and biochemical properties of glycosylated enzyme, a recombinant β-d-glucuronidase (PGUS-P) from Penicillium purpurogenum as a model glycoprotein, was deglycosylated with peptide-N-glycosidase F (PNGase-F) under native conditions. The enzymatic deglycosylation procedure resulted in the complete removal of carbohydrate moiety. Compared with the glycosylated PGUS-P, the deglycosylated PGUS-P exhibited 20-70% higher activity (p<0.05) within pH 6-9, but 15-45% lower activity (p<0.05) at 45-70°C. The apparent decrease in the thermal stability of the deglycosylated enzyme was reflected by a decrease in the denaturation temperature (T(d)) values determined by differential scanning calorimetry (DSC). The removal of N-linked glycans also reduced enzymes sensitivity to certain metal ions. The deglycosylated PGUS-P displayed lower K(m) vaules, but higher k(cat)/K(m) ratios than the glycosylated isoform towards glycyrrhizin. The consequent conformational changes were also determined by circular dichroism (CD) and fluorescence spectroscopy which revealed no significant difference in the secondary but a slight dissimilarity between the tertiary structures of both isoforms of PGUS-P.

Enhancement of (S)-2,3-dichloro-1-propanol production by recombinant whole-cell biocatalyst in n-heptane-aqueous biphasic system.

The enantioselective resolution of (R,S)-2,3-dichloro-1-propanol ((R,S)-DCP) to (S)-DCP by whole cells of a recombinant Escherichia coli expressing halohydrin dehalogenase (HHDH) activity was limited by product inhibition. To solve this problem to improve the productivity of (S)-DCP, an n-heptane-aqueous biphasic system was adopted in this work. The influential operational parameters including phase volumetric ratio, buffer pH and reaction temperature were optimized. Under the optimal reaction conditions, significant improvements of substrate concentration and biocatalyst productivity (375 mM and 7.64 mmol (S)-DCP g(-1) cell) were achieved in this n-heptane-aqueous biphasic system compared with aqueous single-phase system (150 mM and 2.97 mmol g(-1)cell). The scale-up biosynthesis of (S)-DCP was successfully performed in a 2-L stirred reactor, resulting in a 128.8 mM (S)-DCP with enantiomeric excess of 99.1% and average productivity of 2.07 g (S)-DCPL(-1) h(-1), respectively.

Preparative Enrichment and Separation of Glycyrrhetinic Acid Monoglucuronide from Fermentation Broths with Macroporous Resins

Preparative enrichment and separation of Glycyrrhetinic acid monoglucuronide (GAMG) from the pretreated fermentation broth of glycyrrhizin was studied by using six macroporous resins with different physical and chemical properties. D101 resin showed the maximum effectiveness among the tested resins. The solute affinity towards D101 resin at different temperatures was described in terms of Langmuir and Freundlich isotherms, and the equilibrium experimental data were well-fitted to the two isotherms. The dynamic adsorption and desorption tests were carried out in order to optimize the operational parameters for the efficient separation of GAMG. After one run treatment with D101 resin, the contents of GAMG in the product were increased to 8.2-fold with recovery yields of 93.3%. The process achieved easy and effective enrichment and separation of GAMG with D101 resin, and it could be applied for the large-scale preparation of GAMG from the fermentation broth of glycyrrhizin.

Efficient Recovery of 1-Cyanocyclohexaneacetic Acid by Ion-Exchange Process

Efficient recovery of of 1-CA from the bioreaction mixture was investigated using an ion-exchange (IEX) process. Among seven IEX resins examined, the anion resin 201×7 exhibited the highest adsorption capacity for 1-CA. The Freundlich model has the better description for 1-CA adsorption equilibrium than the Langmuir model. The adsorption kinetics showed that the pseudo-second order model was fitted very well. Dynamic adsorption and desorption experiments have been carried out in a fixed bed column to obtain optimal parameters for the recovery of 1-CA from the bioreaction mixture. Under the optimized conditions, 1-CA was recovered in yield of 91.3% with > 99% HPLC purity.