One-step refolding and purification of disulfide-containing proteins with a C-terminal MESNA thioester

Interdisciplinary gene manipulation, molecular cloning, and recombinant expression of modified human growth hormone isoform-1 in E. coli system

BACKGROUND

Growth hormone (GH) is a hormone that promotes growth, cell reproduction, and cell restoration in humans and animals.

OBJECTIVES

Production of recombinant human growth hormone (rhGH) in Escherichia coli (E. coli) and assessment of its characteristics and proliferation stimulatory activity.

METHODS

The hGH gene was cloned into a pET 3a expression vector and transformed into a competent E. coli cell. The refolded hGH was purified, Western blot and batch fermentation were performed. Cell cytotoxicity was tested on Vero cells, and MALDI-TOF and Nano-LC-ESI MS/MS were used for protein and target peptide analysis.

RESULTS

Induced rhGH was purified with a concentration of 511.9 mg/ml. Western blot confirmed the molecular identity of rhGH, showing a single 22 kDa band. The bacterial growth at OD600 after 24 h in batch fermentation was 9.78 ± 0.26, and wet cell weight (WCWg/L) was 15.2 ± 0.32. Purified rhGH activity on Vero cells was 0.535 IU/mg. LC-MS/MS analysis revealed a score of 70.51 % and coverage of 60.37 %.

CONCLUSION

Biologically active native rhGH protein was successfully expressed in the Prokaryotic system. Our goal is to increase its production on a pilot level in the native form at a high activity effect identical to isoform 1.

Expression and Refolding of the Plant Chitinase From Drosera capensis for Applications as a Sustainable and Integrated Pest Management

Recently, the study of chitinases has become an important target of numerous research projects due to their potential for applications, such as biocontrol pest agents. Plant chitinases from carnivorous plants of the genus Drosera are most aggressive against a wide range of phytopathogens. However, low solubility or insolubility of the target protein hampered application of chitinases as biofungicides. To obtain plant chitinase from carnivorous plants of the genus Drosera in soluble form in E.coli expression strains, three different approaches including dialysis, rapid dilution, and refolding on Ni-NTA agarose to renaturation were tested. The developed « Rapid dilution » protocol with renaturation buffer supplemented by 10% glycerol and 2M arginine in combination with the redox pair of reduced/oxidized glutathione, increased the yield of active soluble protein to 9.5 mg per 1 g of wet biomass. A structure-based removal of free cysteines in the core domain based on homology modeling of the structure was carried out in order to improve the soluble of chitinase. One improved chitinase variant (C191A/C231S/C286T) was identified which shows improved expression and solubility in E. coli expression systems compared to wild type. Computational analyzes of the wild-type and the improved variant revealed overall higher fluctuations of the structure while maintaining a global protein stability. It was shown that free cysteines on the surface of the protein globule which are not involved in the formation of inner disulfide bonds contribute to the insolubility of chitinase from Drosera capensis. The functional characteristics showed that chitinase exhibits high activity against colloidal chitin (360 units/g) and high fungicidal properties of recombinant chitinases against Parastagonospora nodorum. Latter highlights the application of chitinase from D. capensis as a promising enzyme for the control of fungal pathogens in agriculture.

Approaches for peptide and protein cyclisation

The cyclisation of polypeptides can play a crucial role in exerting biological functions, maintaining stability under harsh conditions and conferring proteolytic resistance, as demonstrated both in nature and in the laboratory. To date, various approaches have been reported for polypeptide cyclisation. These approaches range from the direct linkage of N- and C- termini to the connection of amino acid side chains, which can be applied both in reaction vessels and in living systems. In this review, we categorise the cyclisation approaches into chemical methods (e.g. direct backbone cyclisation, native chemical ligation, aldehyde-based ligations, bioorthogonal reactions, disulphide formation), enzymatic methods (e.g. subtiligase variants, sortases, asparaginyl endopeptidases, transglutaminases, non-ribosomal peptide synthetases) and protein tags (e.g. inteins, engineered protein domains for isopeptide bond formation). The features of each approach and the considerations for selecting an appropriate method of cyclisation are discussed.

High Efficient Expression, Purification, and Functional Characterization of Native Human Epidermal Growth Factor in Escherichia coli

Human epidermal growth factor (hEGF) is a small, mitotic growth polypeptide that promotes the proliferation of various cells and is widely applied in clinical practices. However, high efficient expression of native hEGF in Escherichia coli has not been successful, since three disulfide bonds in monomer hEGF made it unable to fold into correct 3D structure using in vivo system. To tackle this problem, we fused Mxe GyrA intein (Mxe) at the C-terminal of hEGF followed by small ubiquitin-related modifier (SUMO) and 10x His-tag to construct a chimeric protein hEGF-Mxe-SUMO-H10. The fusion protein was highly expressed at the concentration of 281 mg/L and up to 59.5% of the total cellular soluble proteins. The fusion protein was purified by affinity chromatography and 29.4 mg/L of native hEGF can be released by thiol induced N-terminal cleavage without any proteases. The mitotic activity in Balb/c 3T3 cells is proliferated by commercial and recombinant hEGF measured with methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay which indicated that recombinant hEGF protein stimulates the cell proliferation similar to commercial protein. This study significantly improved the yield and reduced the cost of hEGF in the recombinant E. coli system and could be a better strategy to produce native hEGF for pharmaceutical development.

An evolved Mxe GyrA intein for enhanced production of fusion proteins

Expressing antibodies as fusions to the non-self-cleaving Mxe GyrA intein enables site-specific, carboxy-terminal chemical modification of the antibodies by expressed protein ligation (EPL). Bacterial antibody-intein fusion protein expression platforms typically yield insoluble inclusion bodies that require refolding to obtain active antibody-intein fusion proteins. Previously, we demonstrated that it was possible to employ yeast surface display to express properly folded single-chain antibody (scFv)-intein fusions, therefore permitting the direct small-scale chemical functionalization of scFvs. Here, directed evolution of the Mxe GyrA intein was performed to improve both the display and secretion levels of scFv-intein fusion proteins from yeast. The engineered intein was shown to increase the yeast display levels of eight different scFvs by up to 3-fold. Additionally, scFv- and green fluorescent protein (GFP)-intein fusion proteins can be secreted from yeast, and while fusion of the scFvs to the wild-type intein resulted in low expression levels, the engineered intein increased scFv-intein production levels by up to 30-fold. The secreted scFv- and GFP-intein fusion proteins retained their respective binding and fluorescent activities, and upon intein release, EPL resulted in carboxy-terminal azide functionalization of the target proteins. The azide-functionalized scFvs and GFP were subsequently employed in a copper-free, strain-promoted click reaction to site-specifically immobilize the proteins on surfaces, and it was demonstrated that the functionalized, immobilized scFvs retained their antigen binding specificity. Taken together, the evolved yeast intein platform provides a robust alternative to bacterial intein expression systems.

RNase A does not translocate the alpha-hemolysin pore

The application of nanopore sensing utilizing the α-hemolysin pore to probe proteins at single-molecule resolution has expanded rapidly. In some studies protein translocation through the α-hemolysin has been reported. However, there is no direct evidence, as yet, that proteins can translocate the α-hemolysin pore. The biggest challenge to obtaining direct evidence is the lack of a highly sensitive assay to detect very low numbers of protein molecules. Furthermore, if an activity based assay is applied then the proteins translocating by unfolding should refold back to an active confirmation for the assay technique to work. To overcome these challenges we selected a model enzyme, ribonuclease A, that readily refolds to an active conformation even after unfolding it with denaturants. In addition we have developed a highly sensitive reverse transcription polymerase chain reaction based activity assay for ribonuclease A. Initially, ribonuclease A, a protein with a positive net charge and dimensions larger than the smallest diameter of the pore, was subjected to nanopore analysis under different experimental conditions. Surprisingly, although the protein was added to the cis chamber (grounded) and a positive potential was applied, the interaction of ribonuclease A with α-hemolysin pore induced small and large blockade events in the presence and the absence of a reducing and/or denaturing agent. Upon measuring the zeta potential, it was found that the protein undergoes a charge reversal under the experimental conditions used for nanopore sensing. From the investigation of the effect of voltage on the interaction of ribonuclease A with the α-hemolysin pore, it was impossible to conclude if the events observed were translocations. However, upon testing for ribonuclease A activity on the trans chamber it was found that ribonuclease A does not translocate the α-hemolysin pore.

Facile chemical functionalization of proteins through intein-linked yeast display

Intein-mediated expressed protein ligation (EPL) permits the site-specific chemical customization of proteins. While traditional techniques have used purified, soluble proteins, we have extended these methods to release and modify intein fusion proteins expressed on the yeast surface, thereby eliminating the need for soluble protein expression and purification. To this end, we sought to simultaneously release yeast surface-displayed proteins and selectively conjugate with chemical functionalities compatible with EPL and click chemistry. Single-chain antibodies (scFv) and green fluorescent protein (GFP) were displayed on the yeast surface as fusions to the N-terminus of the Mxe GyrA intein. ScFv and GFP were released from the yeast surface with either a sulfur nucleophile (MESNA) or a nitrogen nucleophile (hydrazine) linked to an azido group. The hydrazine azide permitted the simultaneous release and azido functionalization of displayed proteins, but nonspecific reactions with other yeast proteins were detected, and cleavage efficiency was limited. In contrast, MESNA released significantly more protein from the yeast surface while also generating a unique thioester at the carboxy-terminus of the released protein. These protein thioesters were subsequently reacted with a cysteine alkyne in an EPL reaction and then employed in an azide-alkyne cycloaddition to immobilize the scFv and GFP on an azide-decorated surface with >90% site-specificity. Importantly, the immobilized proteins retained their activity. Since yeast surface display is also a protein engineering platform, these approaches provide a particularly powerful tool for the rapid assessment of engineered proteins.

Utility of physiologically based absorption modeling in implementing Quality by Design in drug development

To implement Quality by Design (QbD) in drug development, scientists need tools that link drug products properties to in vivo performance. Physiologically based absorption models are potentially useful tools; yet, their utility of QbD implementation has not been discussed or explored much in the literature. We simulated pharmacokinetics (PK) of carbamazepine (CBZ) after administration of four oral formulations, immediate-release (IR) suspension, IR tablet, extended-release (XR) tablet and capsule, under fasted and fed conditions and presented a general diagram of a modeling and simulation strategy integrated with pharmaceutical development. We obtained PK parameters and absorption scale factors (ASFs) by deconvolution of the PK data for IR suspension under fasted condition. The model was validated for other PK profiles of IR formulations and used to predict PK for XR formulations. We explored three key areas where a modeling and simulation approach impacts QbD. First, the model was used to help identify optimal in vitro dissolution conditions for XR formulations. Second, identification of critical formulations variables was illustrated by a parameter sensitivity analysis of mean particle radius for the IR tablet that showed a PK shift with decreased particle radius, C (max) was increased and T (max) was decreased. Finally, virtual trial simulations allowed incorporation of inter-subject variability in the model. Virtual bioequivalence studies performed for two test formulations suggested that an in vitro dissolution test may be a more sensitive discriminative method than in vivo PK studies. In summary, a well-validated predictive model is a potentially useful tool for QbD implementation in drug development.

Chemoselective protein and peptide immobilization on biosensor surfaces

Site-specific immobilization of proteins and peptides on a sensor surface represents a significant challenge for bioanalytical applications such as surface plasmon resonance (SPR). The most common protocols for covalent protein immobilization usually result in heterogeneous presentation of the ligand at the surface, which can in some instances yield conflicting results with analogous data obtained in solution. Here, we discuss two complementary and generic bioconjugation methods that allow chemoselective immobilization of peptides and proteins via either their C-terminus (native chemical ligation) or their N-terminus (oxime ligation). While the protocols described in this chapter were designed for use in a Biacore instrument, the methods should also be applicable to other SPR instruments and, with slight adjustments, to many other types of bioanalytical applications that rely on protein-functionalized surfaces.

Fusion expression and immunogenicity of Bordetella pertussis PTS1-FHA protein: implications for the vaccine development

Mutants of pertussis toxin (PT) S1 subunit and filamentous hemagglutinin (FHA) type I immunodominant domain from Bordetella pertussis (B. pertussis) are considered to be effective candidate antigens for acellular pertussis vaccines; however, the substantial progress is hampered in part for the lack of a suitable in vitro expression system. In this paper, the gene sequences of a S1 mutant C180-R9K/E129G (mS1) and a truncated peptide named Fs from FHA type I immunodominant domain were linked together and constructed to pET22b expression vector as a fusion gene; after inducing with IPTG, it was highly expressed in E. coli BL21 (DE3) as inclusion body. The fusion protein FsmS1 was purified from cell lysates and refolded successfully. The result of Western blotting indicate that it was able to react with both anti-S1 and anti-FHA McAbs; antiserum produced from New Zealand white rabbits immunized with this protein was able to recognize both native PT and FHA antigens as determined by western blotting. These data have provided a novel feasible method to produce PT S1 subunit and FHA type I immunodominant domain in large scale in vitro, which is implicated for the development of multivalent subunit vaccines candidate against B. pertussis infection.

Inteins, valuable genetic elements in molecular biology and biotechnology

Inteins are internal protein elements that self-excise from their host protein and catalyze ligation of the flanking sequences (exteins) with a peptide bond. They are found in organisms in all three domains of life, and in viral proteins. Intein excision is a posttranslational process that does not require auxiliary enzymes or cofactors. This self-excision process is called protein splicing, by analogy to the splicing of RNA introns from pre-mRNA. Protein splicing involves only four intramolecular reactions, and a small number of key catalytic residues in the intein and exteins. Protein-splicing can also occur in trans. In this case, the intein is separated into N- and C-terminal domains, which are synthesized as separate components, each joined to an extein. The intein domains reassemble and link the joined exteins into a single functional protein. Understanding the cis- and trans-protein splicing mechanisms led to the development of intein-mediated protein-engineering applications, such as protein purification, ligation, cyclization, and selenoprotein production. This review summarizes the catalytic activities and structures of inteins, and focuses on the advantages of some recent intein applications in molecular biology and biotechnology.

Efficient, chemoselective synthesis of immunomicelles using single-domain antibodies with a C-terminal thioester

Background

Classical bioconjugation strategies for generating antibody-functionalized nanoparticles are non-specific and typically result in heterogeneous compounds that can be compromised in activity. Expression systems based on self-cleavable intein domains allow the generation of recombinant proteins with a C-terminal thioester, providing a unique handle for site-specific conjugation using native chemical ligation (NCL). However, current methods to generate antibody fragments with C-terminal thioesters require cumbersome refolding procedures, effectively preventing application of NCL for antibody-mediated targeting and molecular imaging.

Results

Targeting to the periplasm of E. coli allowed efficient production of correctly-folded single-domain antibody (sdAb)-intein fusions proteins. On column purification and 2-mercapthoethanesulfonic acid (MESNA)-induced cleavage yielded single-domain antibodies with a reactive C-terminal MESNA thioester in good yields. These thioester-functionalized single-domain antibodies allowed synthesis of immunomicelles via native chemical ligation in a single step.

Conclusion

A novel procedure was developed to obtain soluble, well-folded single-domain antibodies with reactive C-terminal thioesters in good yields. These proteins are promising building blocks for the chemoselective functionalization via NCL of a broad range of nanoparticle scaffolds, including micelles, liposomes and dendrimers.

Strategies for successful recombinant expression of disulfide bond-dependent proteins in Escherichia coli

Bacteria are simple and cost effective hosts for producing recombinant proteins. However, their physiological features may limit their use for obtaining in native form proteins of some specific structural classes, such as for instance polypeptides that undergo extensive post-translational modifications. To some extent, also the production of proteins that depending on disulfide bridges for their stability has been considered difficult in E. coli.

Both eukaryotic and prokaryotic organisms keep their cytoplasm reduced and, consequently, disulfide bond formation is impaired in this subcellular compartment. Disulfide bridges can stabilize protein structure and are often present in high abundance in secreted proteins. In eukaryotic cells such bonds are formed in the oxidizing environment of endoplasmic reticulum during the export process. Bacteria do not possess a similar specialized subcellular compartment, but they have both export systems and enzymatic activities aimed at the formation and at the quality control of disulfide bonds in the oxidizing periplasm.

This article reviews the available strategies for exploiting the physiological mechanisms of bactera to produce properly folded disulfide-bonded proteins.