Antitumor activity of interleukin-21 prepared by novel refolding procedure from inclusion bodies expressed in Escherichia coli

The identification and expression of an interleukin-21 receptor in large yellow croaker (Larimichthys crocea)

BACKGROUND

We identified a homologue of IL-21R (LcIL-21R) in large yellow croaker (Larimichthys crocea, Lc). Our investigation focused on understanding the molecular structural features and immune function of LcIL-21R.

METHODS

We cloned the LcIL-21R gene from the genome of Larimichthys crocea by RT‒PCR, and the molecular and structural characteristics of LcIL-21R were analyzed by a series of protein analysis tools. We used real-time PCR to investigate the tissue distribution of LcIL-21R, and LcIL-21R gene expression regulation was also measured in head kidney leukocytes under trivalent bacterial vaccine or poly (I:C) stimulation.

RESULTS

The open reading frame (ORF) of the LcIL-21R gene is 1629 bp long and encodes a precursor protein of 542 amino acids (aa), with a 23-aa signal peptide and a 519-aa mature peptide containing four putative N-glycosylation sites. LcIL-21R has two fibronectin type III (FNIII)-like domains (D1 and D2), a transmembrane domain, and a cytoplasmic region. A conserved WSXWS motif was also found in the D2 domain. The predicted structure of the extracellular region of LcIL-21R (LcIL-21R-Ex) is highly similar to that of human IL-21R. LcIL-21R was constitutively expressed in all tissues examined, and LcIL-21R mRNA levels were increased in the head kidney and spleen upon inactivated trivalent bacterial vaccine or poly(I:C) stimulation.

CONCLUSIONS

Our results suggest that LcIL-21R shares structural and functional properties with IL-21Rs found in other vertebrates, indicating its potential involvement in the IL-21-mediated immune response to pathogenic infections. These findings contribute to our understanding of the evolutionary conservation of IL-21 signaling and its role in the immune system.

Immune adjuvant effects of interferon-gamma (IFN-γ) of flounder (Paralichthys olivaceus) against Edwardsiella tarda

IFN-γ plays a key role in T-cell activation and the establishment of the adaptive immune response, which has a potential as a cytokine adjuvant in the context of vaccination. In this study, we evaluated the immune adjuvant effects of two forms of flounder (Paralichthys olivaceus) IFN-γ, including pcDNA3.1-IFN-γ (pcIFN-γ) and recombinant IFN-γ (rIFN-γ), and comparatively analyzed the immune responses of flounder to E. tarda subunit vaccine rOmpV. The results showed that vaccination with rOmpV plus pcIFN-γ or rIFN-γ produced a relative percent survival of 57% and 71%, respectively, which were significantly higher than that of the control groups, rOmpV plus pcN3 (36%) or rHis (40%). Compared with the two control groups, vaccination with rOmpV plus pcIFN-γ or rIFN-γ could induce significantly higher levels of specific serum antibodies and sIg + lymphocytes in peripheral blood, spleen and head kidney, and significantly higher upregulated expressions of CD4-1, CD8α, IgM, MHC Ⅰα, MHC Ⅱα, IL-1β and TNF-α were also detected in rOmpV plus pcIFN-γ or rIFN-γ vaccinated fish. In addition, compared with pcIFN-γ, rOmpV co-vaccination with rIFN-γ elicited higher levels of sIg + lymphocytes, specific serum antibodies and several immune-related genes expressions in vaccinated flounder. These results demonstrated that rOmpV co-vaccination with rIFN-γ or pcIFN-γ could both boost the immune responses and evoke highly protective effects against E. tarda, indicating that flounder IFN-γ is a promising adjuvant candidate for fish vaccination via an injection administering route.

Interleukin-2 (IL-2) of flounder (Paralichthys olivaceus) as immune adjuvant enhance the immune effects of E. tarda subunit vaccine OmpV against Edwardsiellosis

In our previous study, we cloned and explored the biological functions of flounder (Paralichthys olivaceus) interleukin-2 (poIL-2), and showed that poIL-2 might have adjuvant potential for fish vaccines. In this study, the adjuvant effects of recombinant and molecular forms of poIL-2 (rIL-2 and pcIL-2) were comparatively analyzed and evaluated in flounder from several aspects by co-vaccination with the recombinant E. tarda OmpV (rOmpV). The results showed that co-vaccination with rOmpV plus rIL-2 or pcIL-2 resulted in a relative percent survival of 71% and 57% respectively, which was significantly higher than the control groups, rOmpV plus rHis (40%) or pcN3 (36%). Immunological analysis showed that: (1) the levels of specific serum antibodies and sIg + lymphocytes in head kidney, spleen and peripheral blood induced by rOmpV plus rIL-2 or pcIL-2 were significantly higher than that in the two control groups; (2) Compared to the two control groups, CD4-1, CD4-2, CD8α, CD8β, MHCIα, MHCIIα, IgM and IFN-γ mRNA levels were also significantly induced by rOmpV plus rIL-2 or pcIL-2; (3) the rOmpV plus rIL-2 could induce higher levels of sIg + lymphocytes, specific serum antibodies and the expressions of all investigated genes than rOmpV plus pcIL-2. These results demonstrated that co-vaccination with rOmpV with rIL-2 or pcIL-2 could induce stronger humoral and cellular immune responses, and evoked higher immune protective efficacy against E. tarda infection, suggesting that poIL-2 could be served as a promising candidate adjuvant and have a potential application in the control of flounder diseases.

A Systematic Protein Refolding Screen Method using the DGR Approach Reveals that Time and Secondary TSA are Essential Variables

Refolding of proteins derived from inclusion bodies is very promising as it can provide a reliable source of target proteins of high purity. However, inclusion body-based protein production is often limited by the lack of techniques for the detection of correctly refolded protein. Thus, the selection of the refolding conditions is mostly achieved using trial and error approaches and is thus a time-consuming process. In this study, we use the latest developments in the differential scanning fluorimetry guided refolding approach as an analytical method to detect correctly refolded protein. We describe a systematic buffer screen that contains a 96-well primary pH-refolding screen in conjunction with a secondary additive screen. Our research demonstrates that this approach could be applied for determining refolding conditions for several proteins. In addition, it revealed which “helper” molecules, such as arginine and additives are essential. Four different proteins: HA-RBD, MDM2, IL-17A and PD-L1 were used to validate our refolding approach. Our systematic protocol evaluates the impact of the “helper” molecules, the pH, buffer system and time on the protein refolding process in a high-throughput fashion. Finally, we demonstrate that refolding time and a secondary thermal shift assay buffer screen are critical factors for improving refolding efficiency.

The Immune Adjuvant Effects of Flounder (Paralichthys olivaceus) Interleukin-6 on E. tarda Subunit Vaccine OmpV

Interleukin-6 (IL-6) as a pleiotropic cytokine was widely used as an effective adjuvant for vaccines in mammals. In this study, the immune adjuvant effects of two forms of flounder (Paralichthys olivaceus) IL-6, including recombinant IL-6 (rIL-6) and pcDNA3.1-IL-6 (pcIL-6), were evaluated and comparatively analyzed on E. tarda subunit vaccine recombinant outer membrane protein V (rOmpV). The results showed that the relative percent survivals of flounder vaccinated with rOmpV plus rIL-6 or pcIL-6 were significantly higher than that in the two control groups, rOmpV plus recombinant 6× histidine-tag (rHis) or empty expression vector pcDNA3.1 (pcN3). The levels of specific serum antibodies and surface membrane immunoglobulin-positive (sIg+) lymphocytes in peripheral blood, spleen, and head kidney in the two adjuvant groups were also much higher than that in the two control groups. Compared with the two control groups, higher upregulated expressions of major histocompatibility complex class Iα (MHCIα), cluster of differentiation 8α (CD8α), MHCIIα, CD4-1, interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) were detected in flounder vaccinated with rOmpV plus rIL-6 or pcIL-6 after challenge. In addition, the rOmpV plus rIL-6 could induce significant higher levels of specific serum antibodies, sIg+ lymphocytes and four genes expressions than rOmpV plus pcIL-6. These results demonstrated that both rIL-6 and pcIL-6 used as adjuvants could enhance the immune response and evoke immune protections against E. tarda infection, which has a significant value in controlling diseases using vaccines in flounder.

A zwitterionic polymer as a novel inhibitor of protein aggregation

A zwitterionic polymer was synthesized via RAFT polymerization. This polymer prevented heat induced protein aggregation, by preventing hydrophobic interactions between protein chains in solution, thus acting as a molecular shield.

Refolding techniques for recovering biologically active recombinant proteins from inclusion bodies

Biologically active proteins are useful for studying the biological functions of genes and for the development of therapeutic drugs and biomaterials in a biotechnology industry. Overexpression of recombinant proteins in bacteria, such as Escherichia coli, often results in the formation of inclusion bodies, which are protein aggregates with non-native conformations. As inclusion bodies contain relatively pure and intact proteins, protein refolding is an important process to obtain active recombinant proteins from inclusion bodies. However, conventional refolding methods, such as dialysis and dilution, are time consuming and, often, recovered yields of active proteins are low, and a trial-and-error process is required to achieve success. Recently, several approaches have been reported to refold these aggregated proteins into an active form. The strategies largely aim at reducing protein aggregation during the refolding procedure. This review focuses on protein refolding techniques using chemical additives and laminar flow in microfluidic chips for the efficient recovery of active proteins from inclusion bodies.

Arginine inhibits adsorption of proteins on polystyrene surface

Nonspecific adsorption of protein on solid surfaces causes a reduction of concentration as well as enzyme inactivation during purification and storage. However, there are no versatile inhibitors of the adsorption between proteins and solid surfaces at low concentrations. Therefore, we examined additives for the prevention of protein adsorption on polystyrene particles (PS particles) as a commonly-used material for vessels such as disposable test tubes and microtubes. A protein solution was mixed with PS particles, and then adsorption of protein was monitored by the concentration and activity of protein in the supernatant after centrifugation. Five different proteins bound to PS particles through electrostatic, hydrophobic, and aromatic interactions, causing a decrease in protein concentration and loss of enzyme activity in the supernatant. Among the additives, including arginine hydrochloride (Arg), lysine hydrochloride, guanidine hydrochloride, NaCl, glycine, and glucose, Arg was most effective in preventing the binding of proteins to PS particles as well as activity loss. Moreover, even after the mixing of protein and PS particles, the addition of Arg caused desorption of the bound protein from PS particles. This study demonstrated a new function of Arg, which expands the potential for application of Arg to proteins.

Efficient production of recombinant IL-21 proteins for pre-clinical studies by a two-step dilution refolding method

Produced by CD4(+) helper T cells and natural killer T (NKT) cells, interleukin-21 (IL-21) performs broad regulatory functions on B cells, CD4(+) T cells, CD8(+) T cells, NK cells and NKT cells. Targeting IL-21 to enhance the immune system has attracted great interests in the development of vaccination, anti-infection and anti-tumor therapies. Administration of IL-21 in pre-clinical models is however limited by relatively high expense of the recombinant IL-21 protein. Here, we report a rapid and cost-effective method to produce IL-21 using Escherichia coli (E. coli) by introducing a novel two-step dilution strategy for refolding. The method has been validated to produce milligrams of human IL-21, human IL-21/IL-4 chimera and mouse IL-21 with high bioactivities and low endotoxin, mostly suitable for in vitro and in vivo pre-clinical studies.

Development of an affinity-matured humanized anti-epidermal growth factor receptor antibody for cancer immunotherapy

We showed previously that humanization of 528, a murine anti-epidermal growth factor receptor (EGFR) antibody, causes reduced affinity for its target. Here, to improve the affinity of the humanized antibody for use in cancer immunotherapy, we constructed phage display libraries focused on the complementarity-determining regions (CDRs) of the antibody and carried out affinity selection. Two-step selections using libraries constructed in a stepwise manner enabled a 32-fold affinity enhancement of humanized 528 (h528). Thermodynamic analysis of the interactions between the variable domain fragment of h528 (h528Fv) mutants and the soluble extracellular domain of EGFR indicated that the h528Fv mutants obtained from the first selection showed a large increase in negative enthalpy change due to binding, resulting in affinity enhancement. Furthermore, mutants from the second selection showed a decrease in entropy loss, which led to further affinity maturation. These results suggest that a single mutation in the heavy chain variable domain (i.e. Tyr(52) to Trp) enthalpically contributed for overcoming the energetic barrier to the antigen-antibody interaction, which was a major hurdle for the in vitro affinity maturation of h528. We reported previously that the humanized bispecific diabody hEx3 Db, which targets EGFR and CD3, shows strong anti-tumor activity. hEx3 Db mutants, in which the variable domains of h528 were replaced with those of the affinity-enhanced mutants, were prepared and characterized. In a growth inhibition assay of tumor cells, the hEx3 Db mutants showed stronger anti-tumor activity than that of hEx3 Db, suggesting that affinity enhancement of h528Fv enhances the anti-tumor activity of the bispecific diabody.

Sweeping away protein aggregation with entropic bristles: intrinsically disordered protein fusions enhance soluble expression

Intrinsically disordered, highly charged protein sequences act as entropic bristles (EBs), which, when translationally fused to partner proteins, serve as effective solubilizers by creating both a large favorable surface area for water interactions and large excluded volumes around the partner. By extending away from the partner and sweeping out large molecules, EBs can allow the target protein to fold free from interference. Using both naturally occurring and artificial polypeptides, we demonstrate the successful implementation of intrinsically disordered fusions as protein solubilizers. The artificial fusions discussed herein have a low level of sequence complexity and a high net charge but are diversified by means of distinctive amino acid compositions and lengths. Using 6xHis fusions as controls, soluble protein expression enhancements from 65% (EB60A) to 100% (EB250) were observed for a 20-protein portfolio. Additionally, these EBs were able to more effectively solubilize targets compared to frequently used fusions such as maltose-binding protein, glutathione S-transferase, thioredoxin, and N utilization substance A. Finally, although these EBs possess very distinct physiochemical properties, they did not perturb the structure, conformational stability, or function of the green fluorescent protein or the glutathione S-transferase protein. This work thus illustrates the successful de novo design of intrinsically disordered fusions and presents a promising technology and complementary resource for researchers attempting to solubilize recalcitrant proteins.

Expression and characterization of recombinant interleukin-21 receptor and its targeting single-chain variable fragment antibodies selected from a human phage display library

Interleukin-21 receptor (IL-21R) is widely expressed in lymphocytes, and plays an important role in immunological cell proliferation and cytokine production. The present study aims to express a recombinant extracellular domain of human IL-21R (rhIL-21R-ECD) with high yield, and to screen the anti-IL-21R single-chain variable fragments (scFvs) from a synthetic human phage display library. The rhIL-21R-ECD, being expressed mainly as insoluble inclusion bodies in Escherichia coli BL21 (DE3), was purified and refolded. ELISA analysis showed that the refolded rhIL-21R-ECD bound to its ligand IL-21 in a concentration-dependent manner. Using a phage display technique, anti-IL-21R scFvs were screened from a naïve human phage display library by biopanning. After four rounds of panning, positive clones were isolated, sequenced, and characterized. The clone with highest activity was designated as C2. Flow cytometry analysis showed that the scFv C2 could recognize IL-21R on Jurkat cells. Furthermore, proliferation assay revealed a concentration-dependent inhibitory effect of C2 on the Jurkat cell, with fifty percent inhibitory concentration (IC(50)) of 78 nM. A human scFv antibody C2 with a high binding specificity to IL-21R was isolated and characterized. The antibody showed a concentration-dependent inhibitory effect on Jurkat cell proliferation.

Chemical assistance in refolding of bacterial inclusion bodies

Escherichia coli is one of the most widely used hosts for the production of recombinant proteins but insoluble expression of heterologous proteins is a major bottleneck in production of recombinant proteins in E. coli. In vitro refolding of inclusion body into proteins with native conformations is a solution for this problem but there is a need for optimization of condition for each protein specifically. Several approaches have been described for in vitro refolding; most of them involve the use of additives for assisting correct folding. Cosolutes play a major role in refolding process and can be classified according to their function as aggregation suppressors and folding enhancers. This paper presents a review of additives that are used in refolding process of insoluble recombinant proteins in small scale and industrial processes.

Expression of soluble proteins in Escherichia coli by linkage with the acidic propiece of eosinophil major basic protein

An expression method has been developed to produce soluble cationic polypeptides in Escherichia coli while avoiding inclusion body deposition. For this technique the recombinant product is linked through a thrombin or factor Xa susceptible bond to the amino-terminal domain of the precursor of eosinophil major basic protein (MBP). This N-terminal domain is strongly acidic and is apparently able to shield eosinophils from the potentially injurious activities of MBP. It was reasoned that constructs of this acidic domain with small heterologous cationic proteins expressed in E. coli could result in soluble expression while preventing trafficking and packaging into insoluble inclusion bodies. This has been demonstrated using four examples: complement C5a, CCL18, fibroblast growth factor-β, and leukemia inhibitory factor, whose isoelectric points range from 8.93 to 9.59. Further general applicability of this technique has been shown by using two different expression systems, one which encodes an amino-terminal oligo-histidine leash, and another that codes for an amino-terminal glutathione-S-transferase. Thus the utility of coupling MAP to cationic polypeptides for the purpose of soluble heterologous protein expression in E. coli has been demonstrated.

Solid tumor-targeted infiltrating cytotoxic T lymphocytes retained by a superantigen fusion protein

Successful immune-mediated regression of solid tumors is difficult because of the small number of cytotoxic T lymphocytes (CTLs) that were traffic to the tumor site. Here, the targeting of tumor-specific infiltrating CTLs was dependent on a fusion protein consisting of human epidermal growth factor (EGF) and staphylococcal enterotoxin A (SEA) with the D227A mutation. EGF-SEA strongly restrained the growth of murine solid sarcoma 180 (S180) tumors (control versus EGF-SEA, mean tumor weight: 1.013 versus 0.197 g, difference  = 0.816 g). In mice treated with EGF-SEA, CD4+, CD8+ and SEA-reactive T lymphocytes were enriched around the EGFR expressing tumor cells. The EGF receptors were potentially phosphorylated by EGF-SEA stimulation and the fusion protein promoted T cells to release the tumoricidal cytokines interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α). Intratumoral CTLs secreted cytolytic pore-forming perforins and granzyme B proteins near the surface of carcinomas, causing the death of many tumor cells. We additionally show that labeled EGF-SEA was directly targeted to the tumor tissue after intravenous (i.v.) injection. The findings demonstrate that antibody-like EGF-SEA plays an important role in arresting CTLs in the solid tumor site and has therapeutic potential as a tumor-targeting agent.

Expression, purification, and characterization of recombinant fibulin-5 in a prokaryote expression system

Fibulin-5 is a widely expressed, integrin-binding extracellular matrix protein that mediates endothelial cell adhesion and scaffolds cells to elastic fibers. To investigate anti-angiogenesis activities and context-specific activities on responsive cells of recombinant fibulin-5 (rfibulin-5) expressed in Escherichia coli, the cDNA of fibulin-5 cloned from a human placenta cDNA library was inserted into the pET32a (+) vector to allow fibulin-5 expression as a Trx fusion protein. The fusion protein Trx-fibulin-5, expressed as insoluble inclusion bodies, was solubilized and its resulting expression level reached to 15% of the total cell protein. The Trxfibulin-5 was purified effectively by N(2+)-chelating chromatography and then identified by Western blotting analysis with an anti-His tag antibody. The purified Trx-fibulin-5 was refolded by dialysis against redox reagents, and the rfibulin-5 released from the fusion protein by enterokinase cleavage was purified using a RESOURCE RPC column. The final purified rfibulin-5 effectively inhibited angiogenesis in chicken embryos in a dose-dependent manner through a chorioallantoic membrane (CAM) assay. Additionally, rfibulin-5 potently suppressed in vitro proliferation of human umbilical vein endothelial cells, but stimulated that of human dermal fibroblasts. The expression and in vitro refolding of rfibulin-5 resulted in production of an active molecule with a yield of 2.1 mg/L.

Expression, purification and characterization of recombinant interleukin-21

Interleukin-21 (IL-21) is a key regulator of the immune system. However, studies of this cytokine have so far been hampered by the limited availability of recombinant protein preparations. Here we describe a method based on refolding of inclusion bodies expressed in E. coli by rapid dilution. The method was applied to human and murine IL-21 proteins, which were further purified by affinity chromatography and gel-filtration. The proteins are pure and highly active as determined by endotoxin and cell proliferation assays. The availability of milligram quantities of protein enabled us to generate monoclonal antibody fragments against the cytokine and will aid in further structural, biochemical and physiological analyses.

Ternary system of solution additives with arginine and salt for refolding of beta-galactosidase

(L)-Arginine hydrochloride (Arg HCl) has been used for protein refolding as a universal aggregation suppressor for monomeric proteins. This paper presents an investigation of the refolding of tetrameric beta-galactosidase (beta-gal) using Arg HCl and other salts. In a binary system using only Arg HCl, the refolding yield of beta-gal increased with increasing concentration up to 0.2 M. However, the refolding yield sharply decreased above this concentration, reaching the level below the control yield of 5% at 0.5 M and near zero above 0.75 M, an observation unexpected from monomeric proteins. In a ternary system using both 0.2 M Arg HCl and another salt, the refolding yield increased up to 1.5-fold higher than that in the binary system. These data indicate that aggregation suppressive effects of protein increase with Arg HCl concentration, but also are deleterious to self-association of the protein. This dual nature of Arg HCl effects may have to be taken into account in its application for refolding of oligomeric proteins.

Application of the Fc fusion format to generate tag-free bi-specific diabodies

We previously reported the use of a humanized bi-specific diabody that targets epidermal growth factor receptor and CD3 (hEx3-Db) for cancer immunotherapy. Bacterial expression can be used to express small recombinant antibodies on a large scale; however, their overexpression often results in the formation of insoluble aggregates, and in most cases artificial affinity peptide tags need to be fused to the antibodies for purification by affinity chromatography. Here, we propose a novel method for preparing refined, functional, tag-free bi-specific diabodies from IgG-like bi-specific antibodies (BsAbs) in a mammalian expression system. We created an IgG-like BsAb in which bi-specific diabodies were fused to the human Fc region via a designed human rhinovirus 3C (HRV3C) protease recognition site. The BsAb was purified by protein A affinity chromatography, and the refined tag-free hEx3-Db was efficiently produced from the Fc fusion format by protease digestion. The tag-free hEx3-Db from the Fc fusion format showed a greater inhibition of cancer growth than affinity-tagged hEx3-Db prepared directly from Chinese hamster ovary cells. We also applied our novel method to another small recombinant antibody fragment, hEx3 single-chain diabody (hEx3-scDb), and demonstrated the versatility and advantages of our proposed method compared with papain digestion of hEx3-scDb. This approach may be used for industrial-scale production of functional tag-free small therapeutic antibodies.

Different effects of L-arginine on protein refolding: suppressing aggregates of hydrophobic interaction, not covalent binding

Arginine is one of the most favorable additives in protein refolding. However, arginine does not work for certain disulfide-bond-containing proteins, which is not yet well explained. In this work, refolding of three proteins in the presence of 0-2 M arginine was investigated and compared. Bovine carbonic anhydrase B (CAB), containing no cysteine, was successfully refolded with the help of arginine. The refolding yield could reach almost 100% in the presence of 0.75 M arginine. However, recombinant human colony stimulating factor (rhG-CSF), containing five cysteines, could only achieve 65% refolding yield. The formation of aggregates was found. Blocking of free SH groups of the denatured rhG-CSF by iodoacetamide and subsequently refolding of the protein could reduce the aggregate formation substantially. Further investigation on recombinant green fluorescence protein (GFP), containing two cysteines, also revealed the accumulation of oligomers. The content of oligomers increased with the concentration of arginine, reaching about 30% at 2 M arginine. Comparison of reduced and nonreduced SDS-PAGE revealed that the oligomers were formed through intermolecular disulfide binding. Analysis of the refolding kinetics indicated that intermolecular disulfide bonds were probably formed in the intermediate stage where arginine slowed down the refolding rate and stabilized the intermediates. The accumulated intermediates with unpaired cysteine possessed more chances to react with each other to form oligomers, whereas arginine failed to inhibit disulfide bond formation.

Contributions of interfacial residues of human Interleukin15 to the specificity and affinity for its private alpha-receptor

Human interleukin 15 (hIL15) is a soluble cytokine that plays a key role in the maintenance of long-lasting responses against pathogens and a valuable target for the treatment of autoimmune diseases. In this study, we sought to elucidate the thermodynamic basis of the recognition mechanism for its private alpha-receptor (hIL15Ralpha), considered the first step of the interleukin's activation pathway. Binding of wild-type hIL15 to its alpha-receptor is characterized by a very slow dissociation rate constant and driven by a favorable enthalpy change. We further studied the kinetic and energetic consequences of substituting residues of hIL15 located at the contact interface by means of the surface plasmon resonance technique. Replacement of negatively charged residues with Ala indicates that the energetics of interaction is primarily driven by electrostatic forces, manifested by a dramatic acceleration of the dissociation step and a reduction of favorable binding enthalpy. Our analyses also unveiled a novel and critical role for residue Tyr26 in the interaction, which facilitates desolvation of key charged residues during the assembly of the complex. These results were rationalized in terms of a previously reported structure of hIL15.hIL15alpha, demonstrating that the binding energetics is dominated by interactions occurring at three hot spots whose spatial locations coincide with a previously proposed structural division of the contact interface in three regions. Specifically, Region 1 is the main contributor to the binding energy of the complex by establishing very favorable electrostatic interactions with the receptor; Region 2 is also dominated by electrostatic forces, although of a lesser intensity; and Region 3 confers specificity to the association by means of high shape complementarity and by bringing additional stabilization energy to the complex. The biological impact of hIL15 mutations with the most effect on alpha-receptor binding was evaluated in a cell-based proliferation assay, validating the conclusions of our thermodynamic analyses and highlighting the functional importance of molecular contacts that promote prolonged binding of the interleukin to the alpha-receptor. In closing, the thermodynamics and physicochemical nature of the interactions observed in IL15h.IL15Ralpha complex, together with interactions in Region 3 of the interleukin, poses a stark contrast with the structurally related and sometimes functionally redundant interleukin 2.

Anti-aggregatory effect of cyclodextrins in the refolding process of recombinant growth hormones from Escherichia coli inclusion bodies

Cyclodextrins with different ring size and ring substituents were tested for recombinant mink and porcine growth hormones aggregation suppression in the refolding process from Escherichia coli inclusion bodies. Methyl-beta-cyclodextrin and 2-hydroxypropyl-beta-cyclodextrin show a positive effect on the aggregation suppression of both proteins. The influence of different methyl-beta-cyclodextrin and 2-hydroxypropyl-beta-cyclodextrin concentrations on the renaturation yield of both growth hormones was investigated. Moreover, methyl-beta-cyclodextrin and 2-hydroxypropyl-beta-cyclodextrin suppress not only folding-related, but also temperature-related aggregates formation of both proteins. Circular dichroism experiments (monitoring of protein solution turbidity by registering high tension voltage) showed that the onset temperature of aggregation of both growth hormones increased with increasing 2-hydroxypropyl-beta-cyclodextrin concentration. In conclusion, cyclodextrins have perspectives in biotechnology of veterinary growth hormones not only for protein production, but also for its storage.

An optimised system for refolding of human glucose 6-phosphate dehydrogenase

BACKGROUND

Human glucose 6-phosphate dehydrogenase (G6PD), active in both dimer and tetramer forms, is the key entry enzyme in the pentose phosphate pathway (PPP), providing NADPH for biosynthesis and various other purposes, including protection against oxidative stress in erythrocytes. Accordingly haemolytic disease is a major consequence of G6PD deficiency mutations in man, and many severe disease phenotypes are attributed to G6PD folding problems. Therefore, a robust refolding method with high recovery yield and reproducibility is of particular importance to study those clinical mutant enzymes as well as to shed light generally on the refolding process of large multi-domain proteins.

RESULTS

The effects of different chemical and physical variables on the refolding of human recombinant G6PD have been extensively investigated. L-Arg, NADP+ and DTT are all major positive influences on refolding, and temperature, protein concentration, salt types and other additives also have significant impacts. With the method described here, ~70% enzyme activity could be regained, with good reproducibility, after denaturation with Gdn-HCl, by rapid dilution of the protein, and the refolded enzyme displays kinetic and CD properties indistinguishable from those of the native protein. Refolding under these conditions is relatively slow, taking about 7 days to complete at room temperature even in the presence of cyclophilin A, a peptidylprolyl isomerase reported to increase refolding rates. The refolded protein intermediates shift from dominant monomer to dimer during this process, the gradual emergence of dimer correlating well with the regain of enzyme activity.

CONCLUSION

L-Arg is the key player in the refolding of human G6PD, preventing the aggregation of folding intermediate, and NADP+ is essential for the folding intermediate to adopt native structure. The refolding protocol can be applied to produce high recovery yield of folded protein with unaltered properties, paving the way for future studies on clinical G6PD mutants with folding defects and providing a useful model system to study the folding process of oligomeric proteins.

Thermodynamic consequences of mutations in vernier zone residues of a humanized anti-human epidermal growth factor receptor murine antibody, 528

To investigate the role of Vernier zone residues, which are comprised in the framework regions and underlie the complementarity-determining regions (CDRs) of antibodies, in the specific, high affinity interactions of antibodies with their targets, we focused on the variable domain fragment of murine anti-human epidermal growth factor receptor antibody 528 (m528Fv). Grafting of the CDRs of m528Fv onto a selected framework region of human antibodies, referred to as humanization, reduced the antibody's affinity for its target by a factor of 1/40. The reduction in affinity was due to a substantial reduction in the negative enthalpy change associated with binding. Crystal structures of the ligand-free antibody fragments showed no noteworthy conformational changes due to humanization, and the loop structures of the CDRs of the humanized antibodies were identical to those of the parent antibodies. Several mutants of the CDR-grafted (humanized) variable domain fragment (h528Fv), in which some of the Vernier zone residues in the heavy chain were replaced with the parental murine residues, were constructed and prepared using a bacterial expression system. Thermodynamic analyses of the interactions between the mutants and the soluble extracellular domain of epidermal growth factor receptor showed that several single mutations and a double mutation increased the negative enthalpy and heat capacity changes. Combination of these mutations, however, led to somewhat reduced negative enthalpy and heat capacity changes. The affinity of each mutant for the target was within the range for the wild-type h528Fv, and this similarity was due to enthalpy-entropy compensation. These results suggest that Vernier zone residues make enthalpic contributions to antigen binding and that the regulation of conformational entropy changes upon humanization of murine antibodies must be carefully considered and optimized.

l-Arginine Suppresses Aggregation of Recombinant Growth Hormones in Refolding Process from E. coli Inclusion Bodies

L-Arginine was used to suppress the aggregation of recombinant mink and porcine growth hormones in the refolding process from E. coli inclusion bodies by solubilization-dilution protocol at high protein concentration and pH 8.0. The influence of L-arginine concentration on the renaturation yield of both proteins was investigated. L-Arginine effectively suppressed the precipitation of growth hormones during dilution, but did not inhibit soluble oligomers formation. The results of mink and porcine growth hormones purification from 4 g of biomass are presented.

Human CD4+ central and effector memory T cells produce IL-21: effect on cytokine-driven proliferation of CD4+ T cell subsets

IL-21 regulates certain functions of T cells, B cells, NK cells and dendritic cells. Although activated CD4(+) T cells produce IL-21, data identifying the specific CD4(+) T cell subsets that produce IL-21 are conflicting. In a previous study, mouse IL-21 message was detected in T(H)2, whereas human IL-21 (hIL-21) message was found in both T(H)1 and follicular helper T cells. To identify the IL-21-secreting cell populations in human, we established a hybridoma cell line producing an anti-hIL-21 mAb. Intracellular hIL-21-staining experiments showed that hIL-21 was mainly expressed in activated CD4(+) central memory T cells and in activated CD4(+) effector memory T cells, but not in activated CD4(+) naive T cells. Moreover, IL-21 was produced upon activation by some IFN-gamma-producing T(H)1-polarized cells and some IL-17-producing T(H)17-polarized cells, but not by IL-4-producing T(H)2-polarized cells. These results suggest that specific CD4(+) T cell populations produce IL-21. In the functional analysis, we found that IL-21 significantly enhanced the cytokine-driven proliferation of CD4(+) helper T cells synergistically with IL-7 and IL-15 without T cell activation stimuli. Taken together, IL-21 produced from CD4(+) memory T cells may have a supportive role in the maintenance of CD4(+) T cell subsets.

Highly effective recombinant format of a humanized IgG-like bispecific antibody for cancer immunotherapy with retargeting of lymphocytes to tumor cells

We previously reported the marked in vitro and in vivo antitumor activity of hEx3, a humanized diabody (small recombinant bispecific antibody) with epidermal growth factor receptor (EGFR) and CD3 retargeting. Here, we fabricated a tetravalent IgG-like bispecific antibody with two kinds of single-chain Fv (scFv), i.e. humanized anti-EGFR scFv and anti-CD3 scFv, that contains the same four variable domains as hEx3, on the platform of human IgG1 (hEx3-scFv-Fc). hEx3-scFv-Fc prepared from mammalian cells showed specific binding to both EGFR and CD3 target antigens. At one-thousandth (0.1-100 fmol/ml) of the dose of normal hEx3, hEx3-scFv-Fc showed intense cytotoxicity to an EGFR-positive cell line in a growth-inhibition assay using lymphokine-activated killer cells with the T-cell phenotype (T-LAK cells). The enhanced antitumor effect was more clearly observed when peripheral blood mononuclear cells (PBMCs) were used as effector cells, indicating the utility of IgG-like fabrication. These results suggested that the intense antitumor activity is attributable to the multivalency and the presence of the fused human Fc, a hypothesis that was supported by the results of flow cytometry, PBMC proliferation assay, and protein kinase inhibition assay. Furthermore, the growth inhibition effects of hEx3-scFv-Fc were considerably superior to those of the approved therapeutic antibody, cetuximab, which recognizes the same EGFR antigen even when using PBMCs as effector cells. The high potency of hEx3-scFv-Fc may translate into improved antitumor therapy and lower costs of production because of the smaller doses needed.

High IL-21 receptor expression and apoptosis induction by IL-21 in follicular lymphoma

We surveyed IL-21 receptor (IL-21R) in leukemia and lymphoma and found that follicular lymphoma cells showed exceptionally high IL-21R expression. Notably, IL-21 showed divergent effects depending on the cell origin: growth stimulation in Burkitt lymphoma cell lines and adult T cell leukemia/lymphoma cell lines but induction of apoptosis in B lymphoma cell lines with t(14;18)(q32;q21), a marker karyotype of follicular lymphoma. IL-21 activated caspase-8 and -3 and reduced mitochondrial membrane potential. More importantly, IL-21 decreased Bcl-2 expression but increased Bax expression. These results support a new therapeutic approach using the IL-21/IL-21R system in follicular lymphoma.

An Open-Label, Two-Arm, Phase I Trial of Recombinant Human Interleukin-21 in Patients with Metastatic Melanoma

Purpose: Human interleukin-21 (IL-21) is a pleiotropic class I cytokine that activates CD8+ T cells and natural killer cells. We report a phase 1 study of recombinant human IL-21 in patients with surgically incurable metastatic melanoma. The primary objective was to investigate safety and tolerability by determining dose-limiting toxicity (DLT). The secondary objectives were to identify a dose response for various biomarkers in the peripheral blood, estimate the minimum biologically effective dose, determine the pharmacokinetics of IL-21, determine if anti-IL-21 antibodies were induced during therapy, and measure effects on tumor size according to Response Evaluation Criteria in Solid Tumors.

Experimental Design: Open-label, two-arm, dose escalation trial of IL-21 administered by i.v. bolus injection at dose levels from 1 to 100 μg/kg using two parallel treatment regimens: thrice weekly for 6 weeks (3/wk) or three cycles of daily dosing for 5 days followed by 9 days of rest (5+9).

Results: Twenty-nine patients entered the study. IL-21 was generally well tolerated and no DLTs were observed at the 1, 3, and 10 μg/kg dose levels. In the 3/wk regimen, DLTs were increased in alanine aminotransferase, neutropenia, and lightheadedness with fever and rigors. DLTs in the 5+9 regimen were increased in aspartate aminotransferase and alanine aminotransferase, neutropenia, fatigue, and thrombocytopenia. The maximum tolerated dose was declared to be 30 μg/kg for both regimens. Effects on biomarkers were observed at all dose levels, including increased levels of soluble CD25 and up-regulation of perforin and granzyme B mRNA in CD8+ cells. One partial tumor response observed after treatment with IL-21 for 2 × 6 weeks (3/wk) became complete 3 months later.

Conclusions: IL-21 is biologically active at all dose levels administered and is generally well tolerated, and phase 2 studies have commenced using 30 μg/kg in the 5+9 regimen.

l-Argininamide improves the refolding more effectively than l-arginine

L-arginine (Arg) is a widely used additive for suppressing protein aggregation during refolding. Systematic screening of Arg analogs provides superior additives that enhance the refolding yield more effectively than Arg. The refolding yield of hen egg lysozyme in the presence of 500 mM L-argininamide (ArgAd) increases 1.7-fold higher than Arg. Thermal unfolding experiments indicate that ArgAd has a greater denaturing effect than Arg. The refolding yield positively relates to the net charge of Arg analogs. Moreover ArgAd was also effective for the refolding of bovine carbonic anhydrase. High potency to increase the refolding yield of ArgAd compared to Arg results from high positive net charge and the denaturing property.

A newly proposed mechanism for arginine-assisted protein refolding--not inhibiting soluble oligomers although promoting a correct structure

Arginine has been demonstrated to be capable of suppressing aggregation during protein refolding. However, the pathway and the mechanism for arginine to participate in and to assist refolding process still remains unclear. In this study, arginine-assisted refolding of recombinant consensus interferon (rIFN-con1) was investigated. It was found that although arginine minimized the formation of protein precipitate, it failed to prevent the formation of the soluble oligomeric species. The amount of the oligomers increased with the increase in arginine concentration. This phenomenon has not been reported. On the other hand, arginine was able to promote the yield of correctly refolded rIFN-con1, which was more than 2 times higher than that in the absence of arginine. A proposed mechanism is the stabilization of different soluble species by arginine, which slowed down the conformational movement. The stabilization effect on native-like structure formation overwhelmed the oligomeric promotion effect, which resulted in a composite effect of increased refolding yield for rIFN-con1 when arginine concentration was below 0.5M.

A novel protein refolding method using a zeolite

We have succeeded in developing a simple and effective protein refolding method using the inorganic catalyst, beta-zeolite. The method involves the adsorption of proteins solubilized with 6M guanidine hydrochloride from inclusion body (IB) preparations onto the zeolite. The denaturant is then removed, and the proteins in the IBs are released from the zeolite with polyoxyethylene detergent and salt. All of the IBs tested (11 different species) were successfully refolded under these conditions. The refolded proteins are biochemically active, and NMR analysis of one of the proteins (replication protein A 8) supports the conclusion that correct refolding does occur. Based on these results, we discuss the refolding mechanism.

Expression in Escherichia coli and disulfide bridge mapping of PSC33, an allergenic 2S albumin from peanut

In this work, we describe the expression, purification, and disulfide mapping of the named 'peanut seed cDNA 33' (PSC33) peanut allergen. A variant of PSC33 (with N(63), E(64), Q(69) instead of D(63), Q(64), E(69)) has been identified in peanut by proteomic analysis of a highly IgE immunoreactive purification fraction. It is 92% homologous to Ara h 6. We raised monoclonal antibodies against PSC33 and amplified it by PCR from peanut leaf genomic DNA. PSC33 was intron-less and the two NEQ and DQE variants of PSC33 were equally amplified. Since expression of the natural PSC33 (DQE) gene was very low in Escherichia coli even with supplementation of rare codon tRNAs, a synthetic gene optimized for expression in E. coli of PSC33 (DQE) was introduced into a pET9-c vector. A high production of protein occurred in the inclusion bodies that was submitted to refolding using an additive-introduced stepwise dialysis protocol which consists in the gradual removal of the denaturing agent guanidine-HCl with controlled introduction of oxidized and reduced glutathione and l-arginine as a chemical chaperone. After reverse phase HPLC purification, 1mg of pure refolded protein (as assayed by MALDI-TOF mass spectrometry, mouse IgG immunoreactivity and circular dichroism) were obtained with every 100ml of bacterial culture. Trypsin and CNBr hydrolysis of the protein combined with MALDI-TOF mass spectrometry allowed us to assign disulfide bridges and show that the native and refolded proteins were identical. The four disulfides of canonical 2S albumins were conserved and the two supplementary cysteines of PSC33 were paired together.

Tumor-directed lymphocyte-activating cytokines: refolding-based preparation of recombinant human interleukin-12 and an antibody variable domain-fused protein by additive-introduced stepwise dialysis

Integration of lymphocyte-activating cytokines (e.g., interleukin-12: IL-12) to tumor cells offers promise for cancer immunotherapy, but the preparation of such heterodimeric proteins by refolding is difficult because of subunit instability. We achieved the refolding of Escherichia coli-expressed human IL-12 by a stepwise dialysis method, preventing the formation of insoluble aggregates by adding a redox reagent and an aggregation suppressor. We also constructed a tumor-specific IL-12 protein, each subunit of which was fused with one chain of variable domain fragment (Fv) of anticarcinoembryonic antigen (CEA) antibody T84.66 (aCEA-IL12). Fusion of IL-12 with Fv greatly increased the yield of functional heterodimer. Several assays have indicated that the Fv domain and IL-12 domain of the fused protein had cognate biological activities, and it enhanced the cytotoxicity of T-LAK cells for the cancer cell line.

L-Arginine increases the solubility of unfolded species of hen egg white lysozyme

L-Arginine (L-Arg) has been widely used as an enhancer of protein renaturation. The mechanism behind its action is still not fully understood. Using hen egg white lysozyme as a model protein, we present data that clearly demonstrate the suppression of the aggregation of denatured protein by L-Arg. By chemical modification of free cysteines, a series of unfolded lysozyme species were obtained that served as models for unfolded and intermediate states during the process of oxidative refolding. An increased equilibrium solubility of unfolded species and intermediates in the presence of L-Arg seems to be its major mechanism of action.

In vivo and in vitro roles of IL-21 in inflammation

IL-21 is a cytokine known to mediate its biological action via the IL-21R, composed of a specific chain, IL-21Ralpha, and the common gamma-chain (CD132). Recent data suggest that IL-21 possesses proinflammatory properties. However, there is no clear evidence that IL-21 induces inflammation in vivo and, curiously, the interaction between IL-21 and neutrophils has never been investigated, despite the fact that these cells express CD132 and respond to other CD132-dependent cytokines involved in inflammatory disorders. Using the murine air pouch model, we found that IL-21 induced inflammation in vivo, based on recruitment of neutrophil and monocyte populations. In contrast to LPS, administration of IL-21 into the air pouch did not significantly increase the concentration of IL-6, CCL5, CCL3, and CXCL2. We demonstrated that HL-60 cells expressed IL-21Ralpha, which is down-regulated during their differentiation toward neutrophils, and that IL-21Ralpha is not detected in neutrophils. Concomitant with this, IL-21 induced Erk-1/2 phosphorylation in HL-60 cells, but not in neutrophils. To eliminate the possibility that IL-21 could activate neutrophils even in the absence of IL-21Ralpha, we demonstrated that IL-21 did not modulate several neutrophil functions. IL-21-induced Erk-1/2 phosphorylation was not associated with proliferation or differentiation of HL-60 toward neutrophils, monocytes, or macrophages. IL-21Ralpha was detected in human monocytes and monocyte-derived macrophages, but IL-21 increased CXCL8 production only in monocyte-derived macrophages. We conclude that IL-21 is a proinflammatory cytokine, but not a neutrophil agonist. We propose that IL-21 attracts neutrophils indirectly in vivo via a mechanism independent of IL-6, CCL3, CCL5, and CXCL2 production.

Characterisation and expression analysis of interleukin 2 (IL-2) and IL-21 homologues in the Japanese pufferfish, Fugu rubripes, following their discovery by synteny

This investigation provides the first conclusive evidence for the existence of the interleukin 2 (IL-2) and IL-21 genes in bony fish. The IL-2 and IL-21 sequences have been determined in Fugu rubripes by exploiting the conservation of synteny that is found between regions of the human and Fugu genomes. The predicted 149-amino acid IL-2 homologue contains the IL-2 family signature, has a predicted secondary structure of three alpha helixes and has the two cysteines important in disulphide-bond formation. It shows low amino acid identities (24-34%) with other known IL-2 sequences. The predicted 155-amino acid IL-21 homologue has a predicted secondary structure of four alpha helixes and has the four cysteines important in disulphide-bond formation. It shows low amino acid identities (29-31%) with other known IL-21 sequences. The gene organisation of Fugu IL-2 and IL-21 and the level of synteny between the human and Fugu genomes has been well conserved during evolution, with the order and orientation of the genes matching exactly to human Chromosome 4. Phytohaemagglutinin stimulation of Fugu kidney cells resulted in a large increase in the Fugu IL-2 and IL-21 transcripts. In vivo stimulation of Fugu with LPS and poly I:C showed IL-21 expression to be localised within mucosal tissues. The discovery of IL-2 and IL-21 in fish will now allow more detailed investigations into T-helper cell responses.

Molecular cloning, chromosomal location, and biological activity of porcine interleukin-21

A pig interleukin-21 (IL-21) cDNA was successfully cloned and sequenced from porcine peripheral blood lymphocytes (PBL) stimulated with 10 microg/ml concanavalin A (ConA), 10 microg/ml phytohemagglutinin P (PHA), 50 ng/ml phorbol 12-myristate 13-acetate (PMA), and 0.5 microg/ml anti-porcine CD3 antibody for 48 hr. The open reading frame of the porcine IL-21 cDNA is 459 base pairs in length and encodes 152 amino acids. The predicted amino acid sequence of the porcine IL-21 shows 86.2%, 77.7%, and 58.4% identity to the bovine, human, and murine IL-21, respectively. The porcine IL-21 gene was mapped to porcine chromosome 8 (8q22-->q23) by means of fluorescence in situ hybridization and radiation hybrid mapping, where the porcine IL-2 gene had been mapped nearby. The recombinant porcine mature IL-21 expressed by E. coli induced dose-dependent proliferation and IFN-gamma production from a human NK cell line, NK0. The porcine IL-21 identified in this study will be helpful for the enhancement of innate immune responses of pigs.