Development of a novel Pichia pastoris expression platform via genomic integration of lipase gene for sustained release of methanol from methyloleate.

A novel Lip+ Pichia pastoris expression platform was developed by integrating lipase Lip2 from Yarrowia lipolytica under constitutive Glyceraldehyde-3-phosphate dehydrogenase (GAP) promoter. Effective expression of reporter protein amylase from Bacillus licheniformis was achieved utilizing methyloleate in Lip+Amy+host. Lipase hydrolyzed methyloleate into methanol that sustained PAOX1 induction, and oleic acid, which was readily utilized as a carbon source. The protein expression achieved in presence of methyloleate was comparable to methanol-induced cells, along with an increase in productive biomass. In Lip+Amy+ host, total amylase production of 220.9 ± 13 U/mg biomass was achieved at 96 h using methyloleate supplemented every 24 h. While 206.0 ± 17 U/mg biomass was obtained at 108 h in an Amy+ host induced with methanol every 12 h. Further, lipase expression neither affected growth nor added additional burden on the cellular machinery and no oleic acid accumulation was observed at any time point due to its emulsification and efficient utilization by lipase positive host. Similar results obtained with the second reporter protein γ-cyclodextrin glycosyltransferase (CGTase) from Evansella caseinilytica validated the platform. An alternate lipase Lip11 from Y. lipolytica was also employed in developing a Lip+ host to validate disparity between lipase background and PAOX1 induction in presence of methyloleate.

Hippophae rhamnoides L. rhizobacteria exhibit diversified cellulase and pectinase activities.

Hippophae rhamnoides L. provides an enormous range of medicinal and nutritional benefits. The significant abilities of this plant to survive in Himalayan high altitudes enticed our study to investigate its rhizosphere. Seventeen rhizobacterial strains were isolated from the rhizospheric soil and plant root nodules, belonging to genus Frankia, Azorhizobium, Bacillus, Paenibacillus, Brevibacillus and Pseudomonas, as identified by 16SrRNA sequencing. This varying bacterial population was further examined for the presence of root degrading enzymes pectinase and cellulase, which enable them to intrude the plant roots. Based on the growth and substrate utilization by these rhizobacteria on pectinase screening agar medium and Mandels and Reese agar medium, all the seventeen strains were identified as pectinase and cellulase producing rhizobacteria. The quantitative analysis by DNS method demonstrated varying enzyme activities, spot-lighting the physiological variation in the microbiome. The divergence in the enzyme activities shown by all the strains was analysed statistically, using the software ASSISTAT.

Engineering of deglycosylated and plasmin resistant variants of recombinant streptokinase in Pichia pastoris.

Streptokinase, a therapeutically important thrombolytic agent, is prone to C-terminal degradation and plasmin-mediated proteolytic processing. Since the protein was glycosylated during secretion from Pichia pastoris, therefore, the role of carbohydrate moieties on its stability was analyzed via in vivo blocking of N-glycosylation using tunicamycin where an increased degradation of streptokinase was observed. Further, the in vitro site-directed mutagenesis of the three putative N-glycosylation sites at asparagine residues 14, 265, and 377 to alanine revealed the essentiality of glycosylation of the 14th amino acid residue in its post-translational proteolytic stability without significantly affecting its biological activity. However, the mutation of both Asn265 and Asn377 did not seem to contribute toward its glycosylation but resulted in a 39% lower specific activity in case of the rSK-N265,377A. Moreover, the mutation of all three glycosylation positions drastically reduced the secretory expression of native streptokinase from 347 to 186.6 mg/L for the triple mutant with a 14% lower specific activity of 56,738 IU/mg from 65,808 IU/mg. The secondary structure, tertiary structure, and thermal transition point (45-55 °C) of all the deglycosylated variants did not show any significant differences when compared with fully glycosylated native streptokinase using CD and fluorescence spectroscopy. Furthermore, the longer acting plasmin-resistant variants were also developed via the mutation of lysine residues 59 and 386 to glutamine which enhanced its biological stability as a ~ 1.5-fold increase in the caseinolytic zone size was observed in case of rSK-K59Q and also in rSK-K59,386Q mutant without affecting the structural properties.

High-level expression and efficient refolding of therapeutically important recombinant human Interleukin-3 (hIL-3) in E. coli.

Human interleukin-3 (hIL-3) is a pleiotropic cytokine that stimulates the differentiation and proliferation of multipotent hematopoietic cells thus making it a therapeutically important molecule. In this study, its poor expression yield was improved by addressing various upstream bottlenecks in E. coli heterologous system. The codon-optimized hIL-3 gene was cloned under various signal sequences and solubility enhancer fusion tags for its hyper-expression under a strong T7 promoter. The optimization of shake flask expression studies resulted in a hIL-3 protein concentration of 225 mg/L in the form of inclusion bodies (IBs). Lowering of inducer concentration and cultivation temperature did not improve its solubility. The hIL-3 protein was refolded from IBs and resulted a protein recovery yield of 53% after optimization of refolding conditions. The refolded protein was subsequently purified using Ni-NTA affinity chromatography and gave ∼95% pure protein. The conformational properties of the refolded hIL-3 protein were studied by CD and fluorescence spectrometry where protein showed 40% α-helix and 12% ß-sheets with a fluorescence emission maxima at 344 nm. The molecular identity was further confirmed by MALDI-TOF/TOF and western blot analysis. The biological activity of refolded protein was confirmed via cell proliferation assay on human erythroleukemia TF-1 cells where commercial hIL-3 was taken as a standard control.

A combinatorial approach of N-terminus blocking and codon optimization strategies to enhance the soluble expression of recombinant hIL-7 in E. coli fed-batch culture.

Human interleukin-7 (hIL-7) is a therapeutically important cytokine involved in lymphocyte development and survival. In previous reports, a uniformly poor expression of hIL-7 has been shown in Escherichia coli host with the problem of inclusion body formation. In this study, the role of codon optimization and N-terminus blocking using various solubility enhancer fusion tags was explored to improve its soluble expression. The use of codon optimization strategy improved its expression to 80 ± 5 mg/L at shake flask level. The utilization of pelB leader sequence resulted in an unprocessed protein in the form of cytoplasmic inclusion bodies with lower expression yields. The N-terminus fusion of small ubiquitin-like modifier (SUMO), thioredoxin (Trx), and NusA tags increased the expression in the range of 90-140 mg/L, where >90 % of the fusion protein was obtained in soluble form. The fed-batch fermentation of SUMO-tagged hIL-7 protein was optimized at bioreactor level, where a high volumetric product concentration of 2.65 g/L was achieved by controlling the plasmid segregation instability using high antibiotic concentration. The specific product yield (YP/X) and volumetric product concentration were 1.38 and 2.55-fold higher compared to batch results, respectively. A preparative scale affinity chromatography resulted in a high recovery yield of 50.6 mg/L with ∼90 % purity. The conformational property of purified recombinant hIL-7 from CD spectroscopy showed a typical helical structure with 31.5 % α-helix and 26.43 % ß-sheet. The biological activity of purified protein was tested using IL-7-dependent murine immature B lymphocyte (2E8) cell line by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide salt (MTT) assay, where it showed a similar biological activity as standard control.

Bioprocess development for extracellular production of recombinant human interleukin-3 (hIL-3) in Pichia pastoris.

Human interleukin-3 (hIL-3) is a therapeutically important cytokine involved in the maturation and differentiation of various cells of the immune system. The codon-optimized hIL-3 gene was cloned in fusion with the N-terminus α-mating factor signal peptide of Saccharomyces cerevisiae under an inducible alcohol oxidase 1 (AOX1) and constitutive glyceraldehyde-3-phosphate dehydrogenase (GAP) promoter. A Zeocin concentration up to 2000 mg/L was used to select hyper-producers. The shake flask cultivation studies in the Pichia pastoris GS115 host resulted a maximum recombinant hIL-3 expression level of 145 mg/L in the extracellular medium under the control of AOX1 promoter. The batch fermentation strategy allowed us to attain a fairly pure glycosylated hIL-3 protein in the culture supernatant at a final concentration of 475 mg/L with a high volumetric productivity of 4.39 mg/L/h. The volumetric product concentration achieved at bioreactor level was 3.28 folds greater than the shake flask results. The 6x His-tagged protein was purified using Ni-NTA affinity chromatography and confirmed further by western blot analysis using anti-6x His tag antibody. The glycosylation of recombinant hIL-3 protein was confirmed in a PNGase F deglycosylation reaction where it showed a molecular weight band pattern similar to E. coli produced non-glycosylated hIL-3 protein. The structural properties of recombinant hIL-3 protein were confirmed by CD and fluorescence spectroscopy where protein showed 40 % α-helix, 12 % ß-sheets with an emission maxima at 343 nm. MALDI-TOF-TOF analysis was used to establish the protein identity. The biological activity of purified protein was confirmed by the human erythroleukemia TF-1 cell proliferation assay.

Designing Ubiquitin-like protease 1 (Ulp1) based nano biocatalysts: A promising technology for SUMO fusion proteins.

The SUMO proteases (Ulps), a group of cysteine proteases, are well known for their efficient ability to perform structure-based cleavage of SUMO tag from the protein of interest and generation of biotherapeutics with authentic N-terminus. However, the stability of Ulps has remained a challenge for the economical production of difficult-to-produce proteins in E. coli. Therefore, the present study aimed to establish the methodology for developing stable S. pombe Ulp1 preparation using different enzyme immobilization strategies. The whole-cell biocatalyst developed using the Pir1 anchor protein of Pichia cleaved the SUMO tag within 24 h of reaction incubation. The chemical immobilization using commercial epoxy and amino methacrylate beads significantly enhanced the operational reusability of SpUlp1 up to 24 cycles. Silica beads further improved the repetitive usage of the immobilized enzyme for 65 cycles. The SpUlp1 immobilization on laboratory-developed chitosan-coated iron oxide nanoparticles exhibited more than 90 % cleavage of SUMO tag from different substrates even after 100 consecutive reactions. Moreover, an effective SUMO tag removal was observed within 10 min of incubation. The operational stability of the immobilized enzyme was confirmed in a pH range of 5 to 13. The spherical nature of nanoparticles was confirmed by FESEM and TEM results. The successful chitosan coating and subsequent activation with glutaraldehyde were established via FT-IR. Furthermore, HRTEM, SAED, and XRD proved the crystalline nature of nanoparticles, while VSM confirmed the superparamagnetic behavior.

Challenges and Opportunities in the Process Development of Chimeric Vaccines.

Vaccines are integral to human life to protect them from life-threatening diseases. However, conventional vaccines often suffer limitations like inefficiency, safety concerns, unavailability for non-culturable microbes, and genetic variability among pathogens. Chimeric vaccines combine multiple antigen-encoding genes of similar or different microbial strains to protect against hyper-evolving drug-resistant pathogens. The outbreaks of dreadful diseases have led researchers to develop economical chimeric vaccines that can cater to a large population in a shorter time. The process development begins with computationally aided omics-based approaches to design chimeric vaccines. Furthermore, developing these vaccines requires optimizing upstream and downstream processes for mass production at an industrial scale. Owing to the complex structures and complicated bioprocessing of evolving pathogens, various high-throughput process technologies have come up with added advantages. Recent advancements in high-throughput tools, process analytical technology (PAT), quality-by-design (QbD), design of experiments (DoE), modeling and simulations, single-use technology, and integrated continuous bioprocessing have made scalable production more convenient and economical. The paradigm shift to innovative strategies requires significant attention to deal with major health threats at the global scale. This review outlines the challenges and emerging avenues in the bioprocess development of chimeric vaccines.

Effect of N-glycosylation on secretion, stability, and biological activity of recombinant human interleukin-3 (hIL-3) in Pichia pastoris.

Human interleukin-3 (hIL-3) is a clinically important cytokine used to treat hematological malignancies, bone marrow transplantation, cytopenias, and immunological disorders. The cloning of hIL-3 gene was previously reported by our group, where its expression was optimized under methanol-inducible AOX1 promoter having N-terminal α mating factor signal sequence from Saccharomyces cerevisiae. This study investigated the role of glycosylation pattern on its molecular stability, secretion efficiency, and biological activity using the mutagenesis approach. The two N-linked glycosylation positions at N15th (Asn15) and N70th (Asn70) were sequentially mutated to generate three recombinant hIL-3 variants, i.e., N15A, N70A, and N15/70A. Asparagine at these positions was replaced with non-polar alanine amino acid (Ala, A). The alteration of N-linked glycosylation sites was disadvantageous to its efficient secretion in Pichia pastoris, where a 52.32%, 36.48%, 71.41% lower production was observed in N15A, N70A, and N15/70A mutants, respectively, as compared to native control. The fully glycosylated native hIL-3 protein showed higher thermal stability over its deglycosylated counterparts. The biological activity of native, N15A, N70A, and N15/70A hIL-3 protein was evaluated, where N15/70A mutant showed slightly higher proliferation efficacy than other combinations.

Heterologous expression of novel SUMO proteases from Schizosaccharomyces pombe in E. coli: Catalytic domain identification and optimization of product yields.

Small ubiquitin-related modifier (SUMO) proteins are efficiently used to target the soluble expression of various difficult-to-express proteins in E. coli. However, its utilization in large scale protein production is restricted by the higher cost of Ulp, which is required to cleave SUMO fusion tag from protein-of-interest to generate an authentic N-terminus. This study identified and characterized two novel SUMO proteases i.e., Ulp1 and Ulp2 from Schizosaccharomyces pombe. Codon-optimized gene sequences were cloned and expressed in E. coli. The sequence and structure of SpUlp1 and SpUlp2 catalytic domains were deduced using bioinformatics tools. Protein-protein interaction studies predicted the higher affinity of SpUlp1 towards SUMO compared to its counterpart from Saccharomyces cerevisiae (ScUlp1). The catalytic domain of SpUlp1 was purified using Ni-NTA chromatography with 83.33% recovery yield. Moreover, In vitro activity data further confirmed the fast-acting nature of SpUlp1 catalytic domain, where a 90% cleavage of fusion proteins was obtained within 1 h of incubation, indicating novelty and commercial relevance of S. pombe Ulp1. Biophysical characterization showed 8.8% α-helices, 36.7% ß-sheets in SpUlp1SD. From thermal CD and fluorescence data, SpUlp1SD Tm was found to be 45 °C. Further, bioprocess optimization using fed-batch cultivation resulted in 3.5 g/L of SpUlp1SD production with YP/X of 77.26 mg/g DCW and volumetric productivity of 205.88 mg/L/h.

Isolation of Pichia pastoris PIR genes and their utilization for cell surface display and recombinant protein secretion.

Proteins with internal repeats are highly conserved among budding yeasts. In this study, the isolation of two proteins with internal repeats (PIR) genes, i.e. PpPIR1 and PpPIR2, from the methylotrophic yeast Pichia pastoris has been reported. The PIR1 and PIR2 genes' open reading frames were found to contain 1068 and 972 bases, respectively. The sequence homology search showed a homologous conserved repeat of PIR yeast block (SQIGDGQIQATT) in both proteins. The PIR yeast block was present eight times in the PpPir1p and four times in the PpPir2p proteins. Both proteins showed conserved glutamine (Q) and aspartic acid (D) in the repeated sequences, indicating a possible alkali-sensitive ß1,3-glucan ester linkage. The fusion constructs of PpPir1-2p and enhanced green fluorescent protein (EGFP) were developed for yeast cell surface display. The immunofluorescence assay showed uniform localization of EGFP protein on the P. pastoris cell surface in all fusion constructs. Furthermore, new vectors were developed for recombinant protein secretion in P. pastoris, utilizing the pre-pro signal of PpPir1p protein. Efficient processing of the signal sequence was observed from EGFP and human α1-antitrypsin (AAT) fusion constructs and recombinant protein secretion was obtained in the culture supernatant.

Fungal delignification of lignocellulosic biomass improves the saccharification of cellulosics.

The biological delignification of lignocellulosic feedstocks, Prosopis juliflora and Lantana camara was carried out with Pycnoporus cinnabarinus, a white rot fungus, at different scales under solid-state fermentation (SSF) and the fungal treated substrates were evaluated for their acid and enzymatic saccharification. The fungal fermentation at 10.0 g substrate level optimally delignified the P. juliflora by 11.89% and L. camara by 8.36%, and enriched their holocellulose content by 3.32 and 4.87%, respectively, after 15 days. The fungal delignification when scaled up from 10.0 g to 75.0, 200.0 and 500.0 g substrate level, the fungus degraded about 7.69-10.08% lignin in P. juliflora and 6.89-7.31% in L. camara, and eventually enhanced the holocellulose content by 2.90-3.97 and 4.25-4.61%, respectively. Furthermore, when the fungal fermented L. camara and P. juliflora was hydrolysed with dilute sulphuric acid, the sugar release was increased by 21.4-42.4% and the phenolics content in hydrolysate was decreased by 18.46 and 19.88%, as compared to the unfermented substrate acid hydrolysis, respectively. The reduction of phenolics in acid hydrolysates of fungal treated substrates decreased the amount of detoxifying material (activated charcoal) by 25.0-33.0% as compared to the amount required to reduce almost the same level of phenolics from unfermented substrate hydrolysates. Moreover, an increment of 21.1-25.1% sugar release was obtained when fungal treated substrates were enzymatically hydrolysed as compared to the hydrolysis of unfermented substrates. This study clearly shows that fungal delignification holds potential in utilizing plant residues for the production of sugars and biofuels.

White-rot fungal conversion of wheat straw to energy rich cattle feed.

In order to improve the digestibility and nutrient availability in rumen, wheat straw was subjected to solid state fermentation (SSF) with white-rot fungi (i.e. Pleurotus ostreatus and Trametes versicolor) and the fermented biomass (called myco-straw) was evaluated for biochemical, enzymatic and nutritional parameters. The fungal treatment after 30 days led to significant decrease (P < 0.05) in cell wall constituents viz, acid detergent fiber (ADF), neutral detergent fiber (NDF), hemicellulose, lignin and cellulose to the extent of 35.00, 38.88, 45.00, 37.48 and 37.86%, respectively in P. ostreatus fermented straw, while 30.04, 33.85, 39.90, 31.29 and 34.00%, respectively in T. versicolor fermented straw. However, maximum efficiency of fermentation in terms of low carbohydrate consumption per unit of lignin degradation, favoring cattle feed production was observed for P. ostreatus on the 10th day (17.12%) as compared with T. versicolor on the 30th day (16.91%). The myco-straw was found to contain significantly high (P < 0.05) crude protein (CP; 4.77% T. versicolor, 5.08% P. ostreatus) as compared to control straw (3.37%). Metabolizable energy (ME, MJ/kg DM), percent organic matter digestibility (OMD) and short chain fatty acids (SCFAs; mmol) production also increased considerably from control straw (4.40, 29.91 and 0.292) to a maximum up to P. ostreatus fermented straw (4.92, 33.39 and 0.376 on 20th day) and T. versicolor fermented straw (4.66, 31.74 and 0.334 on 10th day), respectively. Moreover, the myco-straw had lower organic carbon and was rich in nitrogen with lower C/N ratio as compared to control wheat straw. Results suggest that the fungal fermentation of wheat straw effectively improved CP content, OM digestibility, SCFAs production, ME value and simultaneously lowered the C/N ratio, thus showing potential for bioconversion of lignin rich wheat straw into high energy cattle feed.

Nitrogen supplementation ameliorates product quality and quantity during high cell density bioreactor studies of Pichia pastoris: A case study with proteolysis prone streptokinase.

Streptokinase is a well-established cost-effective therapeutic molecule for thrombo-embolic complications. In the current study, a tag-free variant of streptokinase with a native N-terminus (N-rSK) was developed using the Pichia expression system. A three-copy clone was screened that secreted 1062 mg/L of N-rSK in the complex medium at shake flask level. The biologically active (67,552.61 IU/mg) N-rSK recovered by anion exchange chromatography was predicted to contain 15.43% α-helices, 26.43% ß-sheets. The fermentation run in a complex medium yielded a poor quality product due to excessive N-rSK degradation. Therefore, modified basal salt medium was also employed during fermentation operations to reduce the proteolytic processing of the recombinant product. The concomitant feeding of 1 g/L/h soya flour hydrolysate with methanol during the protein synthesis phase reduced the proteolysis and yielded 2.29 g/L of N-rSK. The fermentation medium was also supplemented with urea during growth and induction phases. The combined feeding approach of nitrogen-rich soya flour hydrolysate and urea during bioreactor operations showed significant improvement in protein stability and resulted in a 4-fold increase in N-rSK concentration to a level of 4.03 g/L over shake flask. Under optimized conditions, the volumetric productivity and specific product yield were 52.33 mg/L/h and 33.24 mg/g DCW, respectively.

Bioprocess optimization for the overproduction of catalytic domain of ubiquitin-like protease 1 (Ulp1) from S. cerevisiae in E. coli fed-batch culture.

The exploitation of SUMO (small ubiquitin-related modifier) fusion technology at a large scale for the production of therapeutic proteins with an authentic N-terminus is majorly limited due to the higher cost of ScUlp1 protease. Therefore, the cost-effective production of Saccharomyces cerevisiae Ulp1 protease catalytic domain (402-621 aa) was targeted via its cloning under strong T7 promoter with and without histidine tag. The optimization of cultivation conditions at shake flask resulted in ScUlp1 expression of 195 mg/L in TB medium with a specific product yield of 98 mg/g DCW. The leaky expression of the ScUlp1 protease was controlled using the chemically defined minimal medium. The Ni-NTA affinity purification of ScUlp1 was done near homogeneity using different additives (0.1% Triton X-100, 0.01 mM DTT, 0.02 mM EDTA and 1% glycerol) where a product purity of ∼95% with a recovery yield of 80% was obtained. The specific activity of purified ScUlp1 was found to be 3.986 × 105 U/mg. The ScUlp1 protease successfully cleaved the SUMO tag even at 1:10,000 enzyme to substrate ratio with high efficacy and also showed a comparable catalytic efficiency as of commercial control. Moreover, the in vivo cleavage of SUMO tag via co-expression strategy also resulted in more than 80% cleavage of SUMO fusion protein. The optimization of high cell density cultivation strategies and maintenance of higher plasmid stability at bioreactor level resulted in the ScUlp1 production of 3.25 g/L with a specific product yield of 45.41 mg/g DCW when cells were induced at an OD600 of 132 (63.66 g/L DCW).

Combined effect of gene dosage and process optimization strategies on high-level production of recombinant human interleukin-3 (hIL-3) in Pichia pastoris fed-batch culture.

In this work, the combined effects of gene dosage and process optimization strategies were studied to achieve higher hIL-3 expression in Pichia system. The in-vitro multimerization method was used to generate various Pichia X-33 transformants having multi-copy expression cassettes. The quantitative polymerase chain reaction (qPCR) strategy was used to further confirm the genome integration of hIL-3 expression cassette. From shake flask expression studies, the recombinant hIL-3 concentration in culture supernatant increased upto 8 copies to a level of 310mg/L, thereafter a considerably lower expression was observed. The small scale optimization experiments at shake flask level resulted in an improved product concentration of 350mg/L. The batch and fed-batch fermentation runs in complex medium showed a product concentration of 1.81 and 1.49g/L, respectively. To further enhance the production level, the fermentation runs were conducted in modified minimal media where a maximum hIL-3 protein level of 2.23g/L was obtained in batch fermentation. The specific product yield (YP/X) was at a level of 25.65mg/g DCW, whereas the overall volumetric productivity of the process was 27.31mg/L/h. The biological activity of the partially purified hIL-3 protein was confirmed via the proliferation of human erythroleukemia TF-1 cells using MTT assay.

High level extracellular production of recombinant γ-glutamyl transpeptidase from Bacillus licheniformis in Escherichia coli fed-batch culture.

Increasing demand of microbial γ-glutamyl transpeptidase (GGT) in food and pharmaceutical sectors raised the need for process development for high level production of the enzyme. In this respect, GGT from Bacillus licheniformis ER15 (SBLGGT) was cloned along with its native secretion signal and expressed in E. coli using different expression vectors. Native signal of the enzyme assistedits extracellular translocationin E. coli.Maximum enzyme expression was shown by construct pET51b-sblggt,in comparison to other clones, in E. coli. Shake-flask cultivation and expression using Luria-Bertani (LB) medium resulted in 2800 U/l enzyme titers in 48 h which was furtherenhancedto 4.3-fold after optimizing various cultivation conditions viz. inducer concentration, agitation, medium and induction optical density. High cell density cultivation using fed-batch fermentation strategy resulted in 20-fold increase over shake flask studies to a level of 61250 U/l. After 24 h,the specific product yield was 2355 U/g dry cell weight (DCW)with volumetric productivity of 2552 U/l/h. Of the total enzyme expressed,40% was translocated extracellularly during high cell density fed-batch fermentation resulting in an enzyme activity of 24500 U/l in the extracellular medium after 24 h. This is the highest reported enzyme titers of bacterial GGT enzyme in E. coli expression system. Thus, the current study provides a cost-effective method for the over-expression and preparation of bacterial GGT enzyme for its industrial applications.

The evolution of recombinant thrombolytics: Current status and future directions.

Cardiovascular disorders are on the rise worldwide due to alcohol abuse, obesity, hypertension, raised blood lipids, diabetes and age-related risks. The use of classical antiplatelet and anticoagulant therapies combined with surgical intervention helped to clear blood clots during the inceptive years. However, the discovery of streptokinase and urokinase ushered the way of using these enzymes as thrombolytic agents to degrade the fibrin network with an issue of systemic hemorrhage. The development of second generation plasminogen activators like anistreplase and tissue plasminogen activator partially controlled this problem. The third generation molecules, majorly t-PA variants, showed desirable properties of improved stability, safety and efficacy with enhanced fibrin specificity. Plasmin variants are produced as direct fibrinolytic agents as a futuristic approach with targeted delivery of these drugs using liposome technlogy. The novel molecules from microbial, plant and animal origin present the future of direct thrombolytics due to their safety and ease of administration.

High level production of active streptokinase in Pichia pastoris fed-batch culture.

Streptokinase is a biological macromolecule involved in dissolution of fibrin blood clot and favourably used in various clinical applications. This protein is poorly expressed in soluble form due to its toxic effects on host physiology. The extracellular expression of recombinant streptokinase (SK) with and without 6xHis tag was obtained by cloning its gene under the α-mating factor signal sequence and alcohol inducible AOX1 promoter. Host-vector combinations were optimized to select a hyper producer. From shake flask optimization studies, a maximum expression of 582 mg/L of rSK (non-tagged) and 538 mg/L of rSK-His (His-tagged) protein was obtained when cells were induced at OD600 of 20. The high cell density fermentation increased the volumetric product concentration of rSK-His to a level of 4.25 g/L with a 7.9 folds increase from shake flask results. The specific product yield (YP/X) was 49.75 mg/g DCW along with a high volumetric productivity of 57.43 mg/L/h. The protein was predicted to have 15.43% α-helix and 26.43% ß-sheet with tryptophan emission maxima of around 347 nm. The highest specific activity of rSK-His was 64,903 IU/mg with 1.48 folds purification whereas specific activity of rSK was 55,240 IU/mg with 1.22 folds purification.

Enhancing toxic protein expression in Escherichia coli fed-batch culture using kinetic parameters: Human granulocyte-macrophage colony-stimulating factor as a model system.

The kinetics of recombinant human granulocyte-macrophage colony-stimulating factor (hGM-CSF) expression was studied under the strong T7 promoter in continuous culture of Escherichia coli using complex medium to design an optimum feeding strategy for high cell density cultivation. Continuous culture studies were done at different dilution rates and the growth and product formation profiles were monitored post-induction. Recombinant protein expression was in the form of inclusion bodies with a maximum specific product formation rate (q(p)) of 63.5 mg g(-1) DCW h(-1) at a dilution rate (D) of 0.3 h(-1). The maximum volumetric product concentration achieved at this dilution rate was 474 mg l(-1), which translated a ~1.4 and ~1.75 folds increase than the values obtained at dilution rates of 0.2 h(-1) and 0.4 h(-1) respectively. The specific product yield (Y(P/x)) peaked at 138 mg g(-1) DCW, demonstrating a ~1.6 folds increase in the values obtained at other dilution rates. A drop in q(p) was observed within 5-6 h of induction at all the dilution rates, possibly due to protein toxicity and metabolic stress associated with protein expression. The data from the continuous culture studies allowed us to design an optimal feeding strategy and induction time in fed-batch cultures which resulted in a maximum product concentration of 3.95 g l(-1) with a specific hGM-CSF yield (Y(P/x)) of 107 mg g(-1) DCW.