Stable linker peptides for a cellulose-binding domain-lipase fusion protein expressed in Pichia pastoris

Development of a multigene expression system using 2A peptides in Rhodosporidium toruloides

In eukaryotes, gene expression typically requires individual promoter and terminator for each gene, making the expression of multiple genes tedious and sometimes too difficult to handle. This is especially true for underdeveloped nonmodel organisms with few genetic engineering tools and genetic elements such as Rhodosporidium toruloides. In contrast, polycistronic expression offers advantages such as smaller size and ease of cloning. Here we report the development of a multigene expression system using 2A peptides in R. toruloides. First, twenty-two 2A peptides were evaluated for their cleavage efficiencies, which ranged from 33.65% to 93.32%. Subsequently, the 2A peptide of ERBV-1 with the highest efficiency was selected to enable simultaneous expression of four proteins. In addition, we demonstrated the optimization of the α-linolenic acid biosynthetic pathway using ERBV-1 peptide mediated polycistronic expression, which increased the α-linolenic acid production by 104.72%. These results suggest that using ERBV-1 peptide is an efficient strategy for multigene expression in R. toruloides.

Examination of yield, bacteriolytic activity and cold storage of linker deletion mutants based on endolysin S6_ORF93 derived from Staphylococcus giant bacteriophage S6

Methicillin-resistant Staphylococcus spp. present challenges in clinical and veterinary settings because effective antimicrobial agents are limited. Phage-encoded peptidoglycan-degrading enzyme, endolysin, is expected to be a novel antimicrobial agent. The enzymatic activity has recently been shown to be influenced by the linker between functional domains in the enzyme. S6_ORF93 (ORF93) is one of the endolysins derived from previously isolated Staphylococcus giant phage S6. The ORF93 was speculated to have a catalytic and peptidoglycan-binding domain with a long linker. In this study, we examined the influence of linker shortening on the characteristics of ORF93. We produce wild-type ORF93 and the linker deletion mutants using an Escherichia coli expression system. These mutants were designated as ORF93-Δ05, ORF93-Δ10, ORF93-Δ15, and ORF93-Δ20, from which 5, 10, 15, and 20 amino acids were removed from the linker, respectively. Except for the ORF93-Δ20, ORF93 and its mutants were expressed as soluble proteins. Moreover, ORF93-Δ15 showed the highest yield and bacteriolytic activity, while the antimicrobial spectrum was homologous. The cold storage experiment showed a slight effect by the linker deletion. According to our results and other studies, linker investigations are crucial in endolysin development.

Understanding activity-stability tradeoffs in biocatalysts by enzyme proximity sequencing

Understanding the complex relationships between enzyme sequence, folding stability and catalytic activity is crucial for applications in industry and biomedicine. However, current enzyme assay technologies are limited by an inability to simultaneously resolve both stability and activity phenotypes and to couple these to gene sequences at large scale. Here we present the development of enzyme proximity sequencing, a deep mutational scanning method that leverages peroxidase-mediated radical labeling with single cell fidelity to dissect the effects of thousands of mutations on stability and catalytic activity of oxidoreductase enzymes in a single experiment. We use enzyme proximity sequencing to analyze how 6399 missense mutations influence folding stability and catalytic activity in a D-amino acid oxidase from Rhodotorula gracilis. The resulting datasets demonstrate activity-based constraints that limit folding stability during natural evolution, and identify hotspots distant from the active site as candidates for mutations that improve catalytic activity without sacrificing stability. Enzyme proximity sequencing can be extended to other enzyme classes and provides valuable insights into biophysical principles governing enzyme structure and function.

Research progress of multi-enzyme complexes based on the design of scaffold protein

Multi-enzyme complexes designed based on scaffold proteins are a current topic in molecular enzyme engineering. They have been gradually applied to increase the production of enzyme cascades, thereby achieving effective biosynthetic pathways. This paper reviews the recent progress in the design strategy and application of multi-enzyme complexes. First, the metabolic channels in the multi-enzyme complex have been introduced, and the construction strategies of the multi-enzyme complex emerging in recent years have been summarized. Then, the discovered enzyme cascades related to scaffold proteins are discussed, emphasizing on the influence of the linker on the fusion enzyme (fusion protein) and its possible mechanism. This review is expected to provide a more theoretical basis for the modification of multi-enzyme complexes and broaden their applications in synthetic biology.

Directed evolution of Rhodotorula gracilisd-amino acid oxidase using single-cell hydrogel encapsulation and ultrahigh-throughput screening

Engineering catalytic and biophysical properties of enzymes is an essential step en route to advanced biomedical and industrial applications. Here, we developed a high-throughput screening and directed evolution strategy relying on single-cell hydrogel encapsulation to enhance the performance of d-Amino acid oxidase from Rhodotorula gracilis (RgDAAOx), a candidate enzyme for cancer therapy. We used a cascade reaction between RgDAAOx variants surface displayed on yeast and horseradish peroxidase (HRP) in the bulk media to trigger enzyme-mediated crosslinking of phenol-bearing fluorescent alginate macromonomers, resulting in hydrogel formation around single yeast cells. The fluorescent hydrogel capsules served as an artificial phenotype and basis for pooled library screening by fluorescence activated cell sorting (FACS). We screened a RgDAAOx variant library containing ∼10⁶ clones while lowering the d-Ala substrate concentration over three sorting rounds in order to isolate variants with low K_m. After three rounds of FACS sorting and regrowth, we isolated and fully characterized four variants displayed on the yeast surface. We identified variants with a more than 5-fold lower K_m than the parent sequence, with an apparent increase in substrate binding affinity. The mutations we identified were scattered across the RgDAAOx structure, demonstrating the difficulty in rationally predicting allosteric sites and highlighting the advantages of scalable library screening technologies for evolving catalytic enzymes.

Bioengineered textiles with peptide binders that capture SARS-CoV-2 viral particles

The use of personal protective equipment (PPE), face masks and ventilation are key strategies to control the transmission of respiratory viruses. However, most PPE provides physical protection that only partially prevents the transmission of viral particles. Here, we develop textiles with integrated peptide binders that capture viral particles. We fuse peptides capable of binding the receptor domain of the spike protein on the SARS-CoV-2 capsid to the cellulose-binding domain from the Trichoderma reesei cellobiohydrolase II protein. The hybrid peptides can be attached to the cellulose fibres in cotton and capture SARS-CoV-2 viral particles with high affinity. The resulting bioengineered cotton captures 114,000 infective virus particles per cm2 and reduces onwards SARS-CoV-2 infection of cells by 500-fold. The hybrid peptides could be easily modified to capture and control the spread of other infectious pathogens or for attachment to different materials. We anticipate the use of bioengineered protective textiles in PPE, facemasks, ventilation, and furnishings will provide additional protection to the airborne or fomite transmission of viruses.

Functionalizing Ferritin Nanoparticles for Vaccine Development

In the last decade, the interest in ferritin-based vaccines has been increasing due to their safety and immunogenicity. Candidates against a wide range of pathogens are now on Phase I clinical trials namely for influenza, Epstein-Barr, and SARS-CoV-2 viruses. Manufacturing challenges related to particle heterogeneity, improper folding of fused antigens, and antigen interference with intersubunit interactions still need to be overcome. In addition, protocols need to be standardized so that the production bioprocess becomes reproducible, allowing ferritin-based therapeutics to become readily available. In this review, the building blocks that enable the formulation of ferritin-based vaccines at an experimental stage, including design, production, and purification are presented. Novel bioengineering strategies of functionalizing ferritin nanoparticles based on modular assembly, allowing the challenges associated with genetic fusion to be circumvented, are discussed. Distinct up/down-stream approaches to produce ferritin-based vaccines and their impact on production yield and vaccine efficacy are compared. Finally, ferritin nanoparticles currently used in vaccine development and clinical trials are summarized.

Design of a Novel Multi-Epitope Vaccine Against Echinococcus granulosus in Immunoinformatics

All the time, echinococcosis is a global zoonotic disease which seriously endangers public health all over the world. In order to speed up the development process of anti-Echinococcus granulosus vaccine, at the same time, it can also save economic cost. In this study, immunoinformatics tools and molecular docking methods were used to predict and screen the antigen epitopes of Echinococcus granulosus, to design a multi-epitope vaccine containing B- and T-cell epitopes. The multi-epitope vaccine could activate B lymphocytes to produce specific antibodies theoretically, which could protect the human body against Echinococcus granulosus infection. It also could activate T lymphocytes and clear the infected parasites in the body. In this study, four CD8+ T-cell epitopes, three CD4+ T-cell epitopes and four B-cell epitopes of Protein EgTeg were identified by immunoinformatics methods. Meanwhile, three CD8+ T-cell epitopes, two CD4+ T-cell epitopes and four B-cell epitopes of Protein EgFABP1 were identified. We constructed the multi-epitope vaccine using linker proteins. The study based on the traditional methods of antigen epitope prediction, further optimized the prediction results combined with molecular docking technology and improved the precision and accuracy of the results. Finally, in vivo and in vitro experiments had verified that the vaccine designed in this study had good antigenicity and immunogenicity.

Bio-specific immobilization of enzymes on electrospun PHB nanofibers

Enzyme immobilization provides substantial advantages in terms of improving the efficiency of enzymatic process as well as enhancing the reusability of enzymes. Phasins (PhaPs) are naturally occurring polyhydroxyalkanoate (PHA)-binding proteins, and thus can potentially be used as a fusion partner for oriented immobilization of enzymes onto PHA supports. However, presently available granular PHA supports have low surface-area-to-volume ratio and limited configurational flexibility of enzymatic reactions. In this study, we explored the use of electrospun polyhydroxybutyrate (PHB) nanofibers as an alternative support for high density immobilization of a PhaP-fused lipase. As envisioned, the electrospun PHB nanofibers could anchor 120-fold more enzyme than PHB granules of the same weight. Furthermore, the enzymes immobilized onto the PHB nanofibers exhibited markedly higher stability and activity compared to when immobilized on conventional immobilization supports. Our approach combines the advantageous features of nanofibrous material and specificity of biomolecular interaction for the efficient use of enzymes, which can be widely adopted in the development of various enzymatic processes.

Study of individual domains' functionality in fused lipolytic biocatalysts based on Geobacillus lipases and esterases

The prospects of industrial uses of microbial enzymes have increased greatly during the 21st century. Fused lipolytic enzymes (where one or both fused domains possess lipolytic activity) is a rapidly growing group of industrial biocatalysts. However, the most effective fusion strategy, catalytic behavior of each domain and influence of added linkers on physicochemical and kinetic characteristics of such biocatalysts has not been yet explored. In this study the functionality of individual domains in fused lipolytic enzymes, while using GDEst-lip, GDLip-lip and GDEst-est enzymes as a model system, is analyzed for the first time. Analysis of mutant GDEst-lip, GDLip-lip and GDEst-est variants, where one domain is inactive, showed that both domains retained their activity, although the reduction in specific activity of individual domains has been detected. Moreover, experimental data proposed that the N-terminal domain mostly influenced the thermostability, while the C-terminal domain was responsible for thermal activity. GDEst-lip variants fused by using rigid (EAAELAAE) and flexible (GGSELSGG) linkers indicated that a unique restriction site or a rigid linker is the most preferable fusion strategy to develop new chimeric biocatalysts with domains of Geobacillus lipolytic enzymes.

Regulating Strategies for Producing Carbohydrate Active Enzymes by Filamentous Fungal Cell Factories

Filamentous fungi are important eukaryotic organisms crucial in substrate degradation and carbon cycle on the earth and have been harnessed as cell factories for the production of proteins and other high value-added products in recent decades. As cell factories, filamentous fungi play a crucial role in industrial protein production as both native hosts and heterologous hosts. In this review, the regulation strategies of carbohydrate active enzyme expression at both transcription level and protein level are introduced, and the transcription regulations are highlighted with induction mechanism, signaling pathway, and promoter and transcription factor regulation. Afterward, the regulation strategies in protein level including suitable posttranslational modification, protein secretion enhancement, and protease reduction are also presented. Finally, the challenges and perspectives in this field are discussed. In this way, a comprehensive knowledge regarding carbohydrate active enzyme production regulation at both transcriptional and protein levels is provided with the particular goal of aiding in the practical application of filamentous fungi for industrial protein production.

Anti-Tumor Activity and Pharmacokinetics of AP25-Fc Fusion Protein

AP25 is an anti-tumor peptide with a high affinity for integrins. It exerts its anti-tumor activity by inhibiting angiogenesis and by directly inhibiting the growth of tumor cells. Its half-life time in vivo is only about 50 minutes, which limits its clinical application. In order to prolong the half-life time of AP25 while preserving its anti-tumor activity, several fusion proteins of AP25 and IgG4 Fc were designed and expressed; their anti-tumor activity and pharmacokinetics properties were evaluated. Firstly, four AP25-Fc fusion protein sequences were designed, and the corresponding proteins were expressed and purified. Based on the results of HUVEC migration inhibition assay, HUVEC and tumor cell proliferation inhibition assay and yields of expression by HEK293 cells, the fusion protein designated PSG4R was selected for further evaluation. The anti-tumor effect of PSG4R was then evaluated in vivo on HCT-116 nude mice xenograft model. And the pharmacokinetics properties of PSG4R were investigated in rats. The results showed that PSG4R could inhibit the growth of xenografts of human colon cancer cell line HCT-116 in nude mice by intravenous administration of 40 mg/kg once every two days. The half-life time of PSG4R was 56.270 ± 15.398 h. This study showed that the construction of AP25-Fc fusion protein could significantly prolong the half-life of AP25 while retaining its anti-tumor activity, which provides a new direction for new drug development of AP25.

Co-expression of fat1 and fat2 in transgenic pigs promotes synthesis of polyunsaturated fatty acids

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) are essential for the development and health of mammals, such as humans and livestock. n-3 PUFAs must be supplied by diet due to the absence of a key gene, namely, delta-15 desaturase (fat1), which is responsible for synthesizing n-3 PUFAs from a major type of n-6 PUFAs, linoleic acid (LA). To increase the dietary intake of n-3 PUFAs for humans, fat1-expressing transgenic (TG) livestock have been produced to provide n-3 PUFA-rich meats for humans. However, these TG livestock synthesized n-3 PUFAs from diet-derived, instead of endogenously produced, n-6 PUFAs because they still lack the delta-12 desaturase (fat2) gene for catalyzing conversion of internal oleic acid (OA) to LA. To fill the gap in the de novo n-3 PUFA biosynthesis pathway and to increase n-3 PUFA content in livestock, TG pigs co-expressing fat1-fat2 were generated in the present work. The OA content decreased in fat1-fat2 TG pigs, suggesting that OA was converted to LA by fat2 transgene-encoded delta-12 desaturase. The n-3 PUFA level was elevated, and the n-6/n-3 PUFA ratio dropped in fat1-fat2 TG pigs, revealing that fat1 transgene promoted the synthesis of n-3 PUFAs from n-6 analogs. The expression levels of fatty acid elongase-5 (ELOVL5) and fatty acid elongase-2 (ELOVL2), which are two key enzyme genes for PUFA synthesis, as well as their transcription factor peroxisome proliferator-activated receptor α, increased in fat1-fat2 TG pigs. Thus, the fat1 transgene enhanced n-3 PUFA synthesis by upregulating the expression of enzyme genes involved in the PUFA synthesis pathways. Overall, this study provided a new strategy to produce n-3 PUFA-rich meat for human consumption. The generated fat1-fat2 TG pigs can also serve as a large animal model for studying the roles of n-3 PUFAs in human development and health.

Structural Changes in Stx1 Engineering Monoclonal Antibody Improves Its Functionality as Diagnostic Tool for a Rapid Latex Agglutination Test

Stx1 toxin is one of the AB₅ toxins of Shiga toxin-producing Escherichia coli (STEC) responsible for foodborne intoxication during outbreaks. The single-chain variable fragment (scFv) is the most common recombinant antibody format; it consists of both variable chains connected by a peptide linker with conserved specificity and affinity for antigen. The drawbacks of scFv production in bacteria are the heterologous expression, conformation and stability of the molecule, which could change the affinity for the antigen. In this work, we obtained a stable and functional scFv-Stx1 in bacteria, starting from IgG produced by hybridoma cells. After structural modifications, i.e., change in protein orientation, vector and linker, its solubility for expression in bacteria was increased as well as the affinity for its antigen, demonstrated by a scFv dissociation constant (K_D) of 2.26 × 10^-7 M. Also, it was able to recognize purified Stx1 and cross-reacted with Stx2 toxin by ELISA (Enzyme-Linked Immunosorbent Assay), and detected 88% of Stx1-producing strains using a rapid latex agglutination test. Thus, the scFv fragment obtained in the present work is a bacteria-produced tool for use in a rapid diagnosis test, providing an alternative for STEC diagnosis.

Biomolecular engineering for nanobio/bionanotechnology

Biomolecular engineering can be used to purposefully manipulate biomolecules, such as peptides, proteins, nucleic acids and lipids, within the framework of the relations among their structures, functions and properties, as well as their applicability to such areas as developing novel biomaterials, biosensing, bioimaging, and clinical diagnostics and therapeutics. Nanotechnology can also be used to design and tune the sizes, shapes, properties and functionality of nanomaterials. As such, there are considerable overlaps between nanotechnology and biomolecular engineering, in that both are concerned with the structure and behavior of materials on the nanometer scale or smaller. Therefore, in combination with nanotechnology, biomolecular engineering is expected to open up new fields of nanobio/bionanotechnology and to contribute to the development of novel nanobiomaterials, nanobiodevices and nanobiosystems. This review highlights recent studies using engineered biological molecules (e.g., oligonucleotides, peptides, proteins, enzymes, polysaccharides, lipids, biological cofactors and ligands) combined with functional nanomaterials in nanobio/bionanotechnology applications, including therapeutics, diagnostics, biosensing, bioanalysis and biocatalysts. Furthermore, this review focuses on five areas of recent advances in biomolecular engineering: (a) nucleic acid engineering, (b) gene engineering, (c) protein engineering, (d) chemical and enzymatic conjugation technologies, and (e) linker engineering. Precisely engineered nanobiomaterials, nanobiodevices and nanobiosystems are anticipated to emerge as next-generation platforms for bioelectronics, biosensors, biocatalysts, molecular imaging modalities, biological actuators, and biomedical applications.

Construction of a novel lipolytic fusion biocatalyst GDEst-lip for industrial application

The gene encoding esterase (GDEst-95) from Geobacillus sp. 95 was cloned and sequenced. The resulting open reading frame of 1497 nucleotides encoded a protein with calculated molecular weight of 54.7 kDa, which was classified as a carboxylesterase with an identity of 93-97% to carboxylesterases from Geobacillus bacteria. This esterase can be grouped into family VII of bacterial lipolytic enzymes, was active at broad pH (7-12) and temperature (5-85 °C) range and displayed maximum activity toward short acyl chain p-nitrophenyl (p-NP) esters. Together with GD-95 lipase from Geobacillus sp. strain 95, GDEst-95 esterase was used for construction of fused chimeric biocatalyst GDEst-lip. GDEst-lip esterase/lipase possessed high lipolytic activity (600 U/mg), a broad pH range of 6-12, thermoactivity (5-85 °C), thermostability and resistance to various organic solvents or detergents. For these features GDEst-lip biocatalyst has high potential for applications in various industrial areas. In this work the effect of additional homodomains on monomeric GDEst-95 esterase and GD-95 lipase activity, thermostability, substrate specificity and catalytic properties was also investigated. Altogether, this article shows that domain fusing strategies can modulate the activity and physicochemical characteristics of target enzymes for industrial applications.

Extending the linker region increases the activity of the Bacillus subtilis cellulase CelI15

OBJECTIVES

To investigate the effect of the linker region (LR) on the enzymatic activity, stability, and flexibility of Bacillus subtilis cellulase CelI15, six mutants were constructed that contained increasing numbers of the LR.

RESULTS

The CelI15 mutant with three copies of the LR (approx. 57 amino acids) showed the highest activity, which was almost 20 % greater than that of wild type CelI15. The stability of the mutant enzymes increased as the copy number of the LR decreased. However, the substrate affinity of the mutant enzymes increased as the LR copy number increased, and the mutant with four copies of the LR exhibited the highest substrate affinity. Additionally, the flexibility of the CelI15 mutants increased as the LR copy number increased from zero to four copies, although it decreased sharply for the mutant with five copies of the LR.

CONCLUSION

The activity of CelI15 was increased by increasing the LR copy number, which could be a potential way to improve its enzymatic properties.

Differential secretion pathways of proteins fused to the Escherichia coli maltose binding protein (MBP) in Pichia pastoris

The Escherichia coli maltose binding protein (MBP) is an N-terminal fusion partner that was shown to enhance the secretion of some heterologous proteins from the yeast Pichia pastoris, a popular host for recombinant protein expression. The amount of increase in secretion was dependent on the identity of the cargo protein, and the fusions were proteolyzed prior to secretion, limiting its use as a purification tag. In order to overcome these obstacles, we used the MBP as C-terminal partner for several cargo peptides. While the Cargo-MBP proteins were no longer proteolyzed in between these two moieties when the MBP was in this relative position, the secretion efficiency of several fusions was lower than when MBP was located at the opposite end of the cargo protein (MBP-Cargo). Furthermore, fluorescence analysis suggested that the MBP-EGFP and EGFP-MBP proteins followed different routes within the cell. The effect of several Pichia pastoris beta-galactosidase supersecretion (bgs) strains, mutants showing enhanced secretion of select reporters, was also investigated on both MBP-EGFP and EGFP-MBP. While the secretion efficiency, proteolysis and localization of the MBP-EGFP was influenced by the modified function of Bgs13, EGFP-MBP behavior was not affected in the bgs strain. Taken together, these results indicate that the location of the MBP in a fusion affects the pathway and trans-acting factors regulating secretion in P. pastoris.

Functionalized silk assembled from a recombinant spider silk fusion protein (Z-4RepCT) produced in the methylotrophic yeast Pichia pastoris

Functional biological materials are a growing research area with potential applicability in medicine and biotechnology. Using genetic engineering, the possibility to introduce additional functions into spider silk-based materials has been realized. Recently, a recombinant spider silk fusion protein, Z-4RepCT, was produced intracellularly in Escherichia coli and could after purification self-assemble into silk-like fibers with ability to bind antibodies via the IgG-binding Z domain. In this study, the use of the methylotrophic yeast Pichia pastoris for production of Z-4RepCT has been investigated. Temperature, pH and production time were influencing the amount of soluble Z-4RepCT retrieved from the extracellular fraction. Purification of secreted Z-4RepCT resulted in a mixture of full-length and degraded silk proteins that failed to self-assemble into fibers. A position in the C-terminal domain of 4RepCT was identified as being subjected to proteolytic cleavage by proteases in the Pichia culture supernatant. Moreover, the C-terminal domain was subjected to glycosylation during production in P. pastoris. These observed alterations of the CT domain are suggested to contribute to the failure in fiber assembly. As alternative approach, Z-4RepCT retrieved from the intracellular fraction, which was less degraded, was used and shown to retain ability to assemble into silk-like fibers after enzymatic deglycosylation.

Carbohydrate-binding module assisting glycosynthase-catalysed polymerizations

Glycosynthase-catalyzed polymerization is enhanced by the addition of a carbohydrate binding module (CBM), either as an isolated protein or fused to the glycosynthase, which results in an increase of the degree of polymerization of the polysaccharide products.

Effects of different interchain linkers on biological activity of an anti-prostate cancer single-chain bispecific antibody

Background

A single-chain bispecific antibody (scBsAb; an engineered antibody), has promising clinical applications. Nonetheless, the effect of different interchain linkers on its activity is poorly understood.

Methods

Gene synthesis was used to splice the anti-γ-seminoprotein single-chain antibody (anti-γ-Sm scFv) gene with the anti-CD3 single-chain antibody (anti-CD3 scFv) gene via different interchain peptide linkers. The Phyre2 software was used to predict spatial configuration of different scBsAbs. Eukaryotic expression vectors carrying scBsAbs were constructed by molecular cloning techniques and these plasmids were transfected into HeLa cells with liposomes. scBsAbs were purified by Ni²⁺-NTA agarose and analysed for antigen binding by an enzyme-linked immunosorbent assay (ELISA). Blood pharmacokinetics and inhibition of prostate tumour growth in nude mice were analysed in in vivo experiments.

Results

Bioinformatics analysis and prediction showed that none of the three linkers, Fc, 205C’, and HSA, had a significant effect on protein folding of anti-γ-Sm scFv or anti-CD3 scFv. Nevertheless, the spatial structures of the three linkers were noticeably different. Anti-γ-Sm × anti-CD3 scBsAb with an Fc, 205C’, or HSA linker was successfully constructed, and these antibodies had similar protein expression levels. ELISA showed that all the three scBsAbs bound to Jurkat cells and the LNCaP membrane antigen, although binding of (205C’)scBsAb was weaker than that of the two parental scFvs (P < 0.05). In contrast, binding strength of (HSA)scBsAb and (Fc)scBsAb was close to that of the parental scFvs (P > 0.05). Pharmacokinetic analysis showed that the half-clearance time of the elimination phase (T_1/2β) for (HSA)scBsAb was the longest: up to 4.4 h. Compared with γ-Sm ScFv, the three scBsAbs all had a much stronger inhibitory effect on the growth of prostate cancer (P < 0.05), but there were no significant differences among the three scBsAbs (P > 0.05).

Conclusions

HSA is the optimal linker for the anti-γ-Sm × anti-CD3 scBsAb and may improve antigen-binding affinity of antibodies and prolong physiological retention time. Interchain linkers affect the function of scBsAbs; these effects may have important implications for construction of antibodies.

Prokaryotic-expressed porcine IFNα1-THYα1 fusion proteins exert IFN and THY activities in vitro

Combined use of interferon (IFN) and thymosin (THY) holds a stronger antiviral effect than when applied individually because of their coordination and complementary action. In this study, prokaryotic expressed porcine IFNα1 (poIFNα1) or the porcine IFNα1-THYα1 fusion protein coding with the Escherichia coli preferred codon sequences connected by the three different linkers were gained in the unlabeled pRSFDDuet-1 expression systems and purified using the strong anion-exchange chromatography and hydrophobic chromatography (among which, one was digested by thrombin because the cleavage site was included in the linker). Then, the activities of IFN and THY in the fusion protein were detected using the cytopathic effect inhibition assay and T-cell activity assays. SDS PAGE and western blotting results showed that the poIFNα1 or the three poIFNα1-THYα1 fusion proteins with three different linkers were expressed solubly in E. coli. The poIFNα1 protein and three types of poIFNα1-THYα1 fusion proteins with >90% purity were gained. The poIFNα1-LinkerB-THYα1 fusion protein showed the highest interferon activity compared with the others (P < 0.001), and the poIFNα1-LinkerA-THYα1 fusion protein highest thymosin activity (P < 0.05). In this study, a preliminary experiment was conducted for the expression of the poIFNα1 and THYα1 fusion proteins.

Protein expression in Pichia pastoris: recent achievements and perspectives for heterologous protein production

Pichia pastoris is an established protein expression host mainly applied for the production of biopharmaceuticals and industrial enzymes. This methylotrophic yeast is a distinguished production system for its growth to very high cell densities, for the available strong and tightly regulated promoters, and for the options to produce gram amounts of recombinant protein per litre of culture both intracellularly and in secretory fashion. However, not every protein of interest is produced in or secreted by P. pastoris to such high titres. Frequently, protein yields are clearly lower, particularly if complex proteins are expressed that are hetero-oligomers, membrane-attached or prone to proteolytic degradation. The last few years have been particularly fruitful because of numerous activities in improving the expression of such complex proteins with a focus on either protein engineering or on engineering the protein expression host P. pastoris. This review refers to established tools in protein expression in P. pastoris and highlights novel developments in the areas of expression vector design, host strain engineering and screening for high-level expression strains. Breakthroughs in membrane protein expression are discussed alongside numerous commercial applications of P. pastoris derived proteins.

Expression and purification of soluble monomeric streptavidin in Escherichia coli

We recently reported the engineering of monomeric streptavidin (mSA) for use in monomeric detection of biotinylated ligands. Although mSA can be expressed functionally on the surface of mammalian cells and yeast, the molecule does not fold correctly when expressed in Escherichia coli. Refolding from inclusion bodies is cumbersome and yields a limited amount of purified protein. Improving the final yield should facilitate its use in biotechnology. We tested the expression and purification of mSA fused to GST, MBP, thioredoxin, and sumo tags to simplify its purification and improve the yield. The fusion proteins can be expressed solubly in E. coli and increase the yield by more than 20-fold. Unmodified mSA can be obtained by proteolytically removing the fusion tag. Purified mSA can be immobilized on a solid matrix to purify biotinylated ligands. Together, expressing mSA as a fusion with a solubilization tag vastly simplifies its preparation and increases its usability in biotechnology.

Construction and expression of a recombinant eukaryotic expression plasmid containing the preS1-preS2-S genes of hepatitis B virus and the granulocyte-macrophage colony stimulating factor gene: A study of its immunomodulatory effects

A total of 10-20% of the population remains unresponsive or weakly responsive to hepatitis B vaccine, which is composed of hepatitis B surface antigen HBsAg (S protein). Therefore, it is necessary to develop a hepatitis B vaccine with a better penetrating and responsive rate. In the present study, a plasmid pVAX1-L-GM was constructed and its immunomodulatory effect of as hepatitis B virus (HBV) DNA vaccine was analyzed through the immunization of BALB/c mice. Immune responses were measured after immunization by anti-HBsAg, proliferation of splenocytes, the number of CD4⁺ and CD8⁺ molecules, CTL cytotoxicity, cytokines of IFN-γ and IL-2 secretion assays. Following the immunization, mice in the pVAX1-L-GM group produced antibody 2 weeks earlier compared to the control plasmid pVAX1 and pVAX1HBsAg groups and antibody levels showed significant differences. Enhanced HBsAg-specific splenocyte proliferation as well as specific cytotoxic activities of splenic CTLs were also detected. Furthermore, pVAX1-L-GM plasmid increased the number of CD4⁺ and CD8⁺ molecules on the surface of the spleen T cell and the level of IFN-γ, IL-2 secretion. pVAX1-L-GM induced a specific immune response in mice and enhanced the immune effect. Thus, a foundation was laid for developing immunogenicity of a better prevention and treatment of HBV via a hepatitis B vaccine.

Cellulase linkers are optimized based on domain type and function: insights from sequence analysis, biophysical measurements, and molecular simulation

Cellulase enzymes deconstruct cellulose to glucose, and are often comprised of glycosylated linkers connecting glycoside hydrolases (GHs) to carbohydrate-binding modules (CBMs). Although linker modifications can alter cellulase activity, the functional role of linkers beyond domain connectivity remains unknown. Here we investigate cellulase linkers connecting GH Family 6 or 7 catalytic domains to Family 1 or 2 CBMs, from both bacterial and eukaryotic cellulases to identify conserved characteristics potentially related to function. Sequence analysis suggests that the linker lengths between structured domains are optimized based on the GH domain and CBM type, such that linker length may be important for activity. Longer linkers are observed in eukaryotic GH Family 6 cellulases compared to GH Family 7 cellulases. Bacterial GH Family 6 cellulases are found with structured domains in either N to C terminal order, and similar linker lengths suggest there is no effect of domain order on length. O-glycosylation is uniformly distributed across linkers, suggesting that glycans are required along entire linker lengths for proteolysis protection and, as suggested by simulation, for extension. Sequence comparisons show that proline content for bacterial linkers is more than double that observed in eukaryotic linkers, but with fewer putative O-glycan sites, suggesting alternative methods for extension. Conversely, near linker termini where linkers connect to structured domains, O-glycosylation sites are observed less frequently, whereas glycines are more prevalent, suggesting the need for flexibility to achieve proper domain orientations. Putative N-glycosylation sites are quite rare in cellulase linkers, while an N-P motif, which strongly disfavors the attachment of N-glycans, is commonly observed. These results suggest that linkers exhibit features that are likely tailored for optimal function, despite possessing low sequence identity. This study suggests that cellulase linkers may exhibit function in enzyme action, and highlights the need for additional studies to elucidate cellulase linker functions.

Pharmaceutical aspects of the recombinant human serum albumin dimer: structural characteristics, biological properties, and medical applications

Human serum albumin is the most abundant protein in the blood. It is clinically used in the treatment of severe hypoalbuminemia and as a plasma expander. The use of albumins as a carrier for drugs is currently being developed, and some are now in the preclinical and clinical trial stages. The main technologies for utilizing an albumin as a drug carrier are protein fusion, polymerization and surface modification, and so on. Among these technologies, albumin dimerization has wide clinical applications as a plasma expander as well as a drug carrier. Despite the fact that many reports have appeared on drugs using an albumin dimer as a carrier, our knowledge of the characteristics of the albumin dimer itself is incomplete. In this review, we summarize the structural characteristics of recombinant albumin dimers produced by two methods, namely, chemical linkage with 1,6-bis(maleimido)hexane and genetically linked with an amino acid linker, and the physicochemical characteristics and biological properties of these preparations. Finally, the potential for pharmaceutical applications of albumin dimers in clinical situations is discussed.

Indipendent and Tandem Expression of a Novel Antimicrobial Peptides Plectasin in Escherichia coli

Plectasin, a novel antimicrobial peptide, is isolated from a saprophytic fungus Pseudoplectania nigrella. Plectasin showed potent antibacterial activity in vitro against Gram-positive, especially the Streptococcus pneumoniae and Streptococcus pneumoniae, including strains resistant to conventional antibiotics. In our previous study, plectasin had been expressed at a high yield as a thioredoxin (Trx) – fused protein in Escherichia coli. However, it couldn’t exhibit the antimicrobial activity unless the Trx-tag had been cleaved, which made the producing process be complicated. Concerning that plectasin has no complex post-translational modification and toxicity on E. coli, on the basis of the former works, we further establish the independent and tandem expression system of plectasin in E. coli. In the present study, the coding sequence of plectasin was obtained from pET32a-PLEC with four primers to amplify the independent and tandem plectasin fragments by overlapping PCR-based gene synthesis, and then cloned into pET22b (+) vector. The recombinant protein was expressed successfully in E. coli with IPTG induction. These works might throw light on the production or study of plectasin, and contribute to the development of novel anti-infectious drugs in the future.

Secretion and proteolysis of heterologous proteins fused to the Escherichia coli maltose binding protein in Pichia pastoris

The Escherichia coli maltose binding protein (MBP) has been utilized as a translational fusion partner to improve the expression of foreign proteins made in E. coli. When located N-terminal to its cargo protein, MBP increases the solubility of intracellular proteins and improves the export of secreted proteins in bacterial systems. We initially explored whether MBP would have the same effect in the methylotrophic yeast Pichia pastoris, a popular eukaryotic host for heterologous protein expression. When MBP was fused as an N-terminal partner to several C-terminal cargo proteins expressed in this yeast, proteolysis occurred between the two peptides, and MBP reached the extracellular region unattached to its cargo. However, in two of three instances, the cargo protein reached the extracellular region as well, and its initial attachment to MBP enhanced its secretion from the cell. Extensive mutagenesis of the spacer region between MBP and its C-terminal cargo protein could not inhibit the cleavage although it did cause changes in the protease target sites in the fusion proteins, as determined by mass spectrometry. Taken together, these results suggested that an uncharacterized P. pastoris protease attacked at different locations in the region C-terminal of the MBP domain, including the spacer and cargo regions, but the MBP domain could still act to enhance the secretion of certain cargo proteins.

Heterologous expression of glycosyl hydrolases in planta: a new departure for biofuels

The concept of expressing non-plant glycosyl hydrolase genes in plant tissue is nearly two decades old, yet relatively little work in this field has been reported. However, resurgent interest in technologies aimed at enabling processes that convert biomass to sugars and fuels has turned attention toward this intuitive solution. There are several challenges facing researchers in this field, including the development of better and more specifically targeted delivery systems for hydrolytic genes, the successful folding and post-translational modification of heterologous proteins and the development of cost-effective process strategies utilizing these transformed plants. The integration of these concepts, from the improvement of biomass production and conversion characteristics to the heterologous production of glycosyl hydrolases in a high yielding bioenergy crop, holds considerable promise for improving the lignocellulosic conversion of biomass to ethanol and subsequently to fuels.

Increasing the homogeneity, stability and activity of human serum albumin and interferon-alpha2b fusion protein by linker engineering

Previous studies in our laboratory have shown that when the N-terminus of interferon-alpha2b (IFN-alpha2b) was directly fused of to the C-terminus of human serum albumin (HSA), the resultant fusion protein (HSA-IFN-alpha2b) was heterogeneous (migrated as doublets on non-reducing SDS-PAGE) and unstable (prone to form covalent aggregates). The heterogeneity and instability of HSA-IFN-alpha2b was ascribed to the structural disturbance between HSA and IFN-alpha2b. To alleviate such structural disturbance, linkers with different lengths (1, 2, 5, 10 amino acid residues) or different conformation (flexible linker (FL, GGGGS), rigid linker (RL, PAPAP) or helix-forming linker (HL, AEAAAKEAAAKA)) were inserted between HSA and IFN-alpha2b. It was demonstrated that linker with 5 amino acid residues was sufficient to separated HSA and IFN-alpha2b effectively, as fusion protein with this linker migrated as single band on non-reducing SDS-PAGE. The fusion proteins with FL, RL and HL linkers were purified to homogeneity with yields of 20%, while the recovery rate of HSA-IFN-alpha2b was only 10%. Accelerated thermal stress tests showed that in contrast to HSA-IFN-alpha2b, fusion proteins with FL, RL and HL linkers were free of aggregates after stored at 37 degrees C for 10 days. Stability tests also revealed that fusion proteins with FL, RL and HL linkers had different susceptibility to hydrolysis, with HSA-RL-IFN-alpha2b being the least susceptible to hydrolysis at pH 6 and 7. Activity assay revealed that the insertion of FL, RL and HL linkers increased the anti-viral activity of fusion protein by 39%, 68% and 115%, respectively.

Changing the N-terminal sequence protects recombinant Plasmodium falciparum circumsporozoite protein from degradation in Pichia pastoris

Proteolytic degradation is the primary obstacle in the use of the yeast Pichia pastoris for the expression of recombinant proteins. During the production of a recombinant Plasmodium falciparum circumsporozoite protein in this system, the (NANP)( n ) repeats region at the N-terminus were completely proteolytically degraded. To remove the potential proteolytic site within the recombinant protein, different strategies were tried, including adjusting the cultivation conditions and mutating the sequence at the junction of the repeat domain and C-terminal region, but the degradation continued. However, modification of the N-terminal sequence by adding an epitope-based peptide to the N-terminus not only protected the repeat domain from cleavage by native proteases during longer induction in the yeast host and purification process, but also stabilized this recombinant protein emulsified with adjuvant ISA720 for at least 6 months. The results showed that proteolytic degradation of the recombinant circumsporozoite protein produced in P. pastoris was amino acid sequence (NANP)-specific, and that this effect was likely dependent on the conformation of the recombinant protein.