Expression of a Lactobacillus casei L-lactate dehydrogenase mutant in Pichia pastoris for asymmetric reduction of phenylpyruvate / 生物工程学报

To improve the productivity of L-phenyllactic acid (L-PLA), L-LcLDH1(Q88A/I229A), a Lactobacillus casei L-lactate dehydrogenase mutant, was successfully expressed in Pichia pastoris GS115. An NADH regeneration system in vitro was then constructed by coupling the recombinant (re) LcLDH1(Q88A/I229A) with a glucose 1-dehydrogenase for the asymmetric reduction of phenylpyruvate (PPA) to L-PLA. SDS-PAGE analysis showed that the apparent molecular weight of reLcLDH1(Q88A/I229A) was 36.8 kDa. And its specific activity was 270.5 U/mg, 42.9-fold higher than that of LcLDH1 (6.3 U/mg). The asymmetric reduction of PPA (100 mmol/L) was performed at 40 °C and pH 5.0 in an optimal biocatalytic system, containing 10 U/mL reLcLDH1(Q88A/I229A), 1 U/mL SyGDH, 2 mmol/L NAD⁺ and 120 mmol/L D-glucose, producing L-PLA with 99.8% yield and over 99% enantiomeric excess (ee). In addition, the space-time yield (STY) and average turnover frequency (aTOF) were as high as 9.5 g/(L·h) and 257.0 g/(g·h), respectively. The high productivity of reLcLDH1(Q88A/I229A) in the asymmetric reduction of PPA makes it a promising biocatalyst in the preparation of L-PLA.

Site-directed mutagenesis of human IL-29 and antineoplastic activity of the recombinant human IL-29 variant / 生物工程学报

To explore the anti-tumor proliferation activity of human interleukin-29 (hIL-29) variant and based on bioinformatics analyzed data of hIL-29, a mutant gene hIL-29(mut33,35) was amplified by site-directed mutagenesis and megaprimer PCR. The hIL-29(mut33,35) was inserted into an eukaryotic expression plasmid pPIC9K and successfully expressed in Pichia pastoris GS115. A recombinant variant protein (rhIL-29(mut33,35)) was purified from the ferment supernatant of the engineering GS115. To observe the antineoplastic activity of the variant rhIL-29(mut33,35), a CCK-8 reagent was used to detect the anti-proliferation effect. Results show that it has strong anti-proliferation effect when acted on liver cancer cell BEL7402, colon cancer cell HCT8 and gastric cancer cell SGC7901. The inhibition ratios of the three tumor cells were (30.99 ± 1.58)%, (22.47 ± 1.37)% and (32.05 ± 2.02)%, respectively. In high dose group, the anti-proliferation effect of the rhIL-29(mut33,35) was stronger than that of wild type rhIL-29 (P < 0.01). This indicates the variant rhIL-29(mut33,35) has potential development value for medicine.

Gene cloning, expression of a feruloyl esterase A and purification of its hydrolysis products / 生物工程学报

To express feruloyl esterase A from Aspergillus oryzae in Pichia pastoris expression system and study its hydrolysis function, explore the conditions and effects of purification for ferulic acid extracts by macroporos resin. Using the total RNA from A. oryzae CICC 40186 as the template, we amplified coding sequence AorfaeA encoding a mature feruloyl esterase A (AorFaeA) by RT-PCR technique. Then, the coding sequence AorfaeA was successfully expressed in Pichia pastoris GS115 mediated by an expression plasmid pPIC9K. The purified recombinant AorFaeA (reAorFaeA) showed one single band on SDS-PAGE with an apparent molecular weight of 39.0 kDa. The maximum activity of reAorFaeA to methyl ferulate, measured by high-performance liquid chromatography (HPLC), was 58.35 U/mg. Then, reAorFaeA was used to release ferulic acid from de-starched wheat bran in the presence of xylanase. The purification tests for ferulic acid from the enzymatic hydrolysate were carried out with preselected macroporous resins. The results showed that macroporous resin HPD-300 had much higher adsorption and desorption capacities. Ferulic acid could be quantitatively recovered by 50% of the eluent concentration at a flow speed of 1 mL/min. Under the purification condition, the recovery ratio of ferulic acid was 92%, and the content of ferulic acid was increased from 0.13% in the raw material to 10.55%. This work exploits the breakdown of ferulic acid by recombinant enzymeand provids a good strategy to its "green production".

Effect of N-terminal disulfide bridge on thermostability of family 11 xylanases / 生物工程学报

A mesophilic xylanase from Aspergillus oryzae, abbreviated to AoXyn11A, belongs to glycoside hydrolase family 11. Using AoXyn11A as the parent, the thermotolerant hybrid xylanase, we constructed AEx11A by substituting its N-terminus with the corresponding region of a hyperthermostable family 11 xylanase, EvXyn11(TS). AoXyn11A- and AEx11A-encoding genes were expressed in Pichia pastoris GS115 separately, and effects of temperatures on expressed products were determined and compared. The optimum temperature (T(opt)) of AEx11A was 75 degrees C and its half-life at 70 degrees C (t1/2(70)) was 197 min, improved as compared with those (T(opt) = 50 degrees C, t1/2(70) = 1.0 min) of AoXyn11A. Homology modeling of the AEx11A's structure and comparison between structures of AEx11A and AoXyn11A revealed that one disulfide bridge (Cys5-Cys32) was introduced into AEx11A resulted from N-terminus substitution. To explore the effect of the disulfide bridge on the thermostability of AEx11A, it was removed from AEx11A by site-directed mutagenesis (C5T). Analytical results show that the T(opt) of the mutant AEx11A (AEx11A(C5T)) dropped to 60 degrees C from 75 degrees C of AEx11A, and its t1/2(70) and t1/2(80) also decreased to 3.0 and 1.0 min from 197 and 25 min.