Response Surface Methodology to Optimize the Expression Efficiency of Recombinant Reteplase.

Background: Over expression of Reteplase enzyme has already been studies in the periplasmic space of Escherichia coli (E. coli). However, the role different factors in its expresssin rate remained to be elucidated. Objectives: Optical cell density (OD), IPTG concentration, and expression time are highly effective in the protein expression rates. Therefore, we aimed to determine the optimum levels of these factors for reteplase expression using response surface methodology (RSM). Materials and Methods: The pET21b plasmid was used to sub-clone the designed reteplase gene. Then, the gene was transformed into E. coli BL21 strain. Induction of expression was done by IPTG and analyzed by the SDS page. experiments were designed using the RMS, while the effects of different conditions were evaluated using the Real time-PCR. Results: Sequence optimization removed all undesirable sequences of the designed gene. Transformation into E. coli BL21 was confirmed with an 1152 bp band on the agarose gel. A 39 kDa expression band on the SDS gel confirmed the gene expression. Performing 20 RSM-designed experiments, the optimum levels for IPTG concentration and OD were determined as 0.34mM and 5.6, respectively. Moreover, the optimum level of expression time was demonstrated to be 11.91 hours. The accuracy of the regression model for reteplase overexpression was confirmed by an F-value equal to 25.31 and a meager probability value [(Prob > F) < 0.0001]. The real-time-PCR results indicated that the performed calculations were highly accurate. Conclusion: The obtained results indicate that IPTG concentration, OD, and expression time are significantly involved in the augmentation of recombinant reteplase expression. To the best of our knowledge, this is the first study to assess the combined effect of these factors on reteplase expression. Further RSM-based experiments would bring about new insights regarding the best conditions for reteplase expression.

Optimization and High Level Production of Recombinant Synthetic Streptokinase in E. coli Using Response Surface Methodology.

Streptokinase (SK) is an extracellular protein comprising 414 amino acids with considerable clinical importance as a commonly used thrombolytic agent. Due to its wide spread application and clinical importance designing more efficient SK production platforms worth investigation. In this regard, a synthetic SK gene was optimized and cloned in to pET21b plasmid for periplasmic expression. Response surface methodology was used to design a total of 20 experiments for optimization of IPTG concentration, post-induction period, and cell density of induction (OD600). The optimum levels of the selected parameters were successfully determined to be 0.28 mM for IPTG concentration, 9.889 H for post induction period, and 3.40768 for cell density (OD600). These settings result in 4.14fold increase in SK production rate of optimum expression conditions (7663 IU/mL) in comparison to the primary expression conditions (1853 IU/mL). Achieving higher yields of SK production in shake flask could lead to more cost effective industrial production of this drug which is the ultimate aim of SK production studies.

Disulfide bonds elimination of endoglucanase II from Trichoderma reesei by site-directed mutagenesis to improve enzyme activity and thermal stability: An experimental and theoretical approach.

EndoglucanaseII (Cel5A) of Trichoderma reesei is widely used industrially with the high catalytic efficiency, but it is not stable high temperatures. Structural comparison with the closest thermophilic endoglucanase homolog, Cel5A from Thermoascus aurantiacus, demonstrates disulfide bond differences. Replacement of Cysteine99 with Valine and Cysteine323 with Histidine by site directed mutagenesis caused elimination of two disulfide bonds. Recombinant expression in Pichia pastoris showed the catalytic efficiency (kcat/Km) increment toward CMC for single mutant enzymes, C99V and C323H, about 1.87 and 1.3 folded respectively. This indicates that the elimination of disulfide bond in substrate binding cleft around the catalytic domain of mutant EndoglucanaseII may be increased the flexibility of protein, to form a suitable E-S complex. In direct contrast with previous studies suggesting the existence of disulfide bonds increase the protein stability, the results showed mutant endoglucanase enzymes with disulfide bond reduction have higher thermal stability. The thermal stability of C99V and C323H in 80 °C were increased 2.4 and 2.34 folded, respectively. In this project, theoretical data had a good agreement with the experimental results. Because of high enzyme activity and thermal stability, both of C99V and C323H mutant have high potential suitable for different industrial applications.

Selective reduction in glutaminase activity of l­Asparaginase by asparagine 248 to serine mutation: A combined computational and experimental effort in blood cancer treatment.

Type II l­asparaginase (l­ASNase) is an FDA approved enzyme drug with extensive applications for treatment of certain blood cancers. However, the therapeutic efficiency of this enzyme is hampered by its undesirable glutaminase activity. Given the pivotal role of this enzyme against cancer, designing engineered mutants with diminished glutaminase activity would be of great therapeutic interest. To this end, N248S mutation was selected as the potential mutation with beneficial effects. Various in silico analyses including MD simulation, molecular docking and QMMM studies were performed to assess the effects of N248S mutation on the activity of the enzyme. Thereafter, this mutation along with N248A, N248V and N248T mutations as controls were exerted in l­ASNase gene. The results from in silico analyses and experimental efforts indicated that N248S mutation is associated with the suitable l­ASNase activity, while the glutaminase activity is disturbed due to impaired interactions. It has been shown that glutamine turnover was affected much more strongly than asparagine hydrolysis. The approach of exploiting in silico tools to design mutated enzymes lead to staggering time and cost reduction. Following this strategy, we have designed a mutant l­ASNase with diminished glutaminase activity, which could be of interest for improved biomedical applications.

Evaluating the efficiency of phiC31 integrase-mediated monoclonal antibody expression in CHO cells.

Traditional methods to generate CHO cell lines rely on random integration(s) of the gene of interest and result in unpredictable and unstable protein expression. In comparison, site-specific recombination methods increase the recombinant protein expression by inserting transgene at a locus with specific expression features. PhiC31 serine integrase, catalyze unidirectional integration that occurs at higher frequency in comparison with the reversible integration carried out by recombinases such as Cre. In this study, using different ratios of phiC31 serine integrase, we evaluated the phiC31 mediated gene integration for expression of a humanized IgG1 antibody (mAb0014) in CHO-S cells. Light chain (LC) and heavy chain (HC) genes were expressed in one operon under EF1α promoter and linked by internal ribosome entry site (IRES) element. The clonal selection was carried out by limiting dilution. Targeted integration approach increased recombinant protein yield and stability in cell pools. The productivity of targeted cell pools was about 4 mg/L and about 40 µg/L in the control cell pool. The number of integrated transgenes was about 19 fold higher than the control cells pools. Our results confirmed that the phiC31 integrase leads to mAb expression in more than 90% of colonies. The productivity of the PhiC31 integrated cell pools was stable for three months in the absence of selection as compared with conventional transfection methods. Hence, utilizing PhiC31 integrase can increase protein titer and decrease the required time for protein expression. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1570-1576, 2016.

Optimization of Recombinant Expression of Synthetic Bacterial Phytase in Pichia pastoris Using Response Surface Methodology.

BACKGROUND: Escherichia coli phytase is an acidic histidine phytase with great specific activity. Pichia pastoris is a powerful system for the heterologous expression of active and soluble proteins which can express recombinant proteins in high cell density fermenter without loss of product yield and efficiently secrete heterologous proteins into the media. Recombinant protein expression is influenced by expression conditions such as temperature, concentration of inducer, and pH. By optimization, the yield of expressed proteins can be increase. Response surface methodology (RSM) has been widely used for the optimization and studying of different parameters in biotechnological processes. OBJECTIVES: In this study, the expression of synthetic appA gene in P. pastoris was greatly improved by adjusting the expression condition. MATERIALS AND METHODS: The appA gene with 410 amino acids was synthesized by P. pastoris codon preference and cloned in expression vector pPinkα-HC, under the control of AOX1 promoter, and it was transformed into P. pastoris GS115 by electroporation. Recombinant phytase was expressed in buffered methanol-complex medium (BMMY) and the expression was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and enzymatic assay. To achieve the highest level of expression, methanol concentration, pH and temperature were optimized via RSM. Finally, the optimum pH and temperature for recombinant phytase activity was determined. RESULTS: Escherichia coli phytase was expressed in P. pastoris under different cultivation conditions (post-induction temperature, methanol concentration, and post-induction pH). The optimized conditions by RSM using face centered central composite design were 1% (v/v) methanol, pH = 5.8, and 24.5°C. Under the optimized conditions, appA was successfully expressed in P. pastoris and the maximum phytase activity was 237.2 U/mL after 72 hours of expression. CONCLUSIONS: By optimization of recombinant phytase expression in shake flask culture, we concluded that P. pastoris was a suitable host for high-level expression of phytase and it can possess high potential for industrial applications.