Protein folding liquid chromatography and its recent developments

Precise modulation of protein refolding by rationally designed covalent organic frameworks

Precisely regulating protein conformation (folding) for biomanufacturing and biomedicine is of great significance but remains challenging. In this work, we innovate a covalent organic framework (COF)-directed protein refolding strategy to modulate protein conformation by rationally designed covalent organic frameworks with adapted pore structures and customizable microenvironments. The conformation of denatured protein can be efficiently recovered through a simple one-step approach using covalent organic framework treatment in aqueous or buffer solutions. This strategy demonstrates high generality that can be applied to various proteins (for example, lysozyme, glucose oxidase, trypsin, nattokinase, and papain) and diverse covalent organic frameworks. An in-depth investigation of the refolding mechanism reveals that pore size and microenvironments such as hydrophobicity, π-π conjugation, and hydrogen bonding are critical to regulating protein conformation. Furthermore, we use this covalent organic framework platform to build up solid-phase columns for continuous protein recovery and achieved a ~ 100% refolding yield and excellent recycling performance (30 cycles), enabling an integrated process for the extracting and refolding denatured proteins (such as the harvest of protein in inclusion bodies). This study creates a highly efficient and customizable covalent organic framework platform for precisely regulating proteins refolding and enhancing their performance, opening up a new avenue for advanced protein manufacturing.

Evolution of myoglobin diffusion mechanisms: exploring pore and surface diffusion in a single silica particle

This study elucidates the mass transfer mechanism of myoglobin (Mb) within a single silica particle with a 50 nm pore size at various pH levels (6.0, 6.5, 6.8, and 7.0). Investigation of Mb distribution ratio (R) and distribution kinetics was conducted using absorption microspectroscopy. The highest R was observed at pH 6.8, near the isoelectric point of Mb, as the electrostatic repulsion between Mb molecules on the silica surface decreased. The time-course absorbance of Mb in the silica particle was rigorously analyzed based on a first-order reaction, yielding the intraparticle diffusion coefficient of Mb (Dp). Dp-(1 + R)-1 plots at different pH values were evaluated using the pore and surface diffusion model. Consequently, we found that at pH 6.0, Mb diffused in the silica particle exclusively through surface diffusion, whereas pore diffusion made a more substantial contribution at higher pH. Furthermore, we demonstrated that Mb diffusion was hindered by slow desorption, associated with the electrostatic charge of Mb. This comprehensive analysis provides insights into the diffusion mechanisms of Mb at acidic, neutral, and basic pH conditions.

Pore Size Dependence of Mass Transfer of Zinc Myoglobin in a Single Mesoporous Silica Particle

This study investigated the pore size dependence of the mass transfer of zinc myoglobin (ZnMb) in a single mesoporous silica particle through confocal fluorescence microspectroscopy. The ZnMb's fluorescence depth profile in the particle was analyzed by a spherical diffusion model, and the intraparticle diffusion coefficient was obtained. The intraparticle diffusion coefficient in the silica particle with various pore sizes (10, 15, 30, and 50 nm) was furthermore analyzed based on a pore and surface diffusion model. Although the mass transfer mechanism in all silica particles followed the pore and surface diffusion model, the adsorption and desorption of ZnMb affected the mass transfer depending on the pore size. The influence of the slow desorption of ZnMb became pronounced for large pore sizes (30 and 50 nm), which was revealed by simulation using a diffusion equation combined with the adsorption-desorption kinetics. The distribution of ZnMb was suppressed in small pore sizes (10 and 15 nm) owing to the adsorption of ZnMb onto the entrance of the pore. Thus, we revealed the mass transfer mechanism of ZnMb in the silica particle with different pore sizes.

Kinetic Analysis of the Mass Transfer of Zinc Myoglobin in a Single Mesoporous Silica Particle by Confocal Fluorescence Microspectroscopy

The adsorption/desorption mechanisms of biomolecules in porous materials have attracted significant attention because of their applications in many fields, including environmental, medical, and industrial sciences. Here, we employ confocal fluorescence microspectroscopy to reveal the diffusion behavior of zinc myoglobin (ZnMb, 4.4 nm × 4.4 nm × 2.5 nm) as a spherical protein in a single mesoporous silica particle (pore size of 15 nm). The measurement of the time course of the fluorescence depth profile of the particle reveals that intraparticle diffusion is the rate-limiting process of ZnMb in the particle. The diffusion coefficients of ZnMb in the particle for the distribution (D_dis) and release (D_re) processes are determined from the rate constants, e.g., D_dis = 1.65 × 10^-10 cm² s^-1 and D_re = 3.68 × 10^-10 cm² s^-1, for a 10 mM buffer solution. The obtained D values for various buffer concentrations are analyzed using the pore and surface diffusion model. Although surface diffusion is the main distribution process, the release process involves pore and surface diffusion, which have not been observed with small organic molecules; the mechanism of transfer of small molecules is pore diffusion alone. We demonstrate that the mass transfer kinetics of ZnMb in the silica particle can be explained well on the basis of pore and surface diffusion.

Stacking of nanorings to generate nanotubes for acceleration of protein refolding

Self-assembly and photoisomerization of azobenzene-based amphiphilic molecules produced nanorings with an inner diameter of 25 nm and lengths of <40 nm. The nanorings, which consisted of a single bilayer membrane of the amphiphiles, retained their morphology in the presence of a stacking inhibitor; whereas in the absence of the inhibitor, the nanorings stacked into short nanotubes (<500 nm). When subjected to mild heat treatment, these nanotubes joined end-to-end to form nanotubes with lengths of several tens of micrometers. The nanorings and the short and long nanotubes were able to encapsulate proteins and thereby suppress aggregation induced by thermal denaturation. In addition, the nanotubes accelerated refolding of denatured proteins by encapsulating them and then releasing them into the bulk solution; refolding occurred simultaneously with release. In contrast, the nanorings did not accelerate protein refolding. Refolding efficiency increased with increasing nanotube length, indicating that the re-aggregation of the proteins was strictly inhibited by lowering the concentration of the proteins in the bulk solution as the result of the slow release from the longer nanotubes. The migration of the proteins through the long, narrow nanochannels during the release process will also contribute to refolding.

Evaluation of Crimean-Congo Hemorrhagic Fever Orthonairovirus AviTagged Nucleoprotein for Potential Application in Diagnosis

Background

Crimean-Congo hemorrhagic fever (CCHF) is an acute viral zoonotic disease, with a mortality rate of 30-50%. There is no approved vaccine or any specific antiviral treatment for CCHF; therefore, the rapid diagnosis seems to be crucial for both efficient supportive therapy and control of infection spread. In this study, the potency of recombinant nucleoprotein of virus expressed in prokaryotic system was investigated for diagnosis of the infection.

Methods

The DNA sequence of complete nucleoprotein ORF was codon optimized based on E. coli codon usage and synthesized commercially. The gene was subcloned in pCA4 vector and expressed in E. coli BL21 (DE3). Refolding and simultaneous purification of nucleoprotein were performed using protein folding liquid chromatography method. The recombinant nucleoprotein was analyzed by Western blotting, ELISA, immunofluorescence assay, and circular dichroism. Forty eight human samples, in three IgM positive and three negative control groups, were evaluated using recombinant nucleoprotein in a capture ELISA setting. Serum from healthy individuals, those suspected to viral hemorrhagic fevers, and positive samples of Chikungunya and Dengue were considered as negative controls.

Results

The existence and structure of recombinant nucleoprotein were verified and confirmed. Capture IgM ELISA detected all positive samples (sensitivity of 100%), but none of the 25 negative samples was detected as positive (specificity of 100%). The test also detected all the included genotypes of virus.

Discussion

Our recombinant nucleoprotein can be used in IgM capture ELISA for easy and efficient detection of CCHF in any lab in endemic regions.

Efficient and easily scalable protein folding strong anion exchange chromatography for renaturation and simultaneous purification of recombinant human asparaginase from E. coli

Recombinant proteins are revolutionizing present day therapeutics. They are generally expressed as insoluble inclusion bodies in the E. coli and mis-folding, loss of protein, and high cost of down streaming are the hurdles in their recovery. For the first time, we are reporting the refolding with simultaneous purification of rhASP in E. coli using a single step utilizing protein folding-strong anion exchange chromatography (PF-SAX). The purification method is also standardized for optimal concentration of solution additives, pH, and mobile phase composition. The results showed purification of rhASP with anion exchange chromatography was effective. Phosphate buffer and slightly alkaline pH produced significant recovery yields and purity profiles. The effect of solution additives such as arginine, glycerol, TMAO, sorbitol, dextran, glutamate, and fructose on rhASP renaturation is also investigated. Significant results were achieved using arginine-TMAO combination in terms of purity, recovery yield and specific activity of 99%, 78%, and 210 IU/mg, respectively. The work concludes that PF-SAX refolding method is superior to other conventional methods and it can be applied to large scale purification of rhASP produced in E. coli. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1036-1044, 2018.

Glycolipid-based nanostructures with thermal-phase transition behavior functioning as solubilizers and refolding accelerators for protein aggregates

The self-assembly of synthetic glycolipids produced nanostructures such as vesicles and nanotubes consisting of bilayer membranes, which underwent a gel-to-liquid crystalline thermal phase transition. Vesicles formed at temperatures above the thermal phase transition temperatures (T_g-l) could solubilize aggregates of denatured proteins by trapping them in the fluid bilayer membranes. Cooling to temperatures below T_g-l caused a morphological transformation into nanotubes that accompanied the thermal phase transition from the fluid to the solid state. This phenomenon allowed the trapped proteins to be quickly released into the bulk solution and simultaneously facilitated the refolding of the proteins. The refolding efficiency strongly depended on the electrostatic attraction between the bilayer membranes of the nanostructures and the proteins. Because of the long shape (>400 nm) of the nanotubes, simple membrane filtration through a pore size of 200 nm led to complete separation and recovery of the refolded proteins (3-9 nm sizes).

Effect of Photoinduced Size Changes on Protein Refolding and Transport Abilities of Soft Nanotubes

Self-assembly of azobenzene-modified amphiphiles (Glyn Azo, n=1-3) in water at room temperature in the presence of a protein produced nanotubes with the protein encapsulated in the channels. The Gly2 Azo nanotubes (7 nm internal diameter [i.d.]) promoted refolding of some encapsulated proteins, whereas the Gly3 Azo nanotubes (13 nm i.d.) promoted protein aggregation. Although the 20 nm i.d. channels of the Gly1 Azo nanotubes were too large to influence the encapsulated proteins, narrowing of the i.d. to 1 nm by trans-to-cis photoisomerization of the azobenzene units of the Gly1 Azo monomers packed in the solid bilayer membranes led to a squeezing out of the proteins into the bulk solution and simultaneously enhanced their refolding ratios. In contrast, photoinduced transformation of the Gly2 Azo nanotubes to short nanorings (<40 nm) with a large i.d. (28 nm) provided no further refolding assistance. We thus demonstrate that pertubation by the solid bilayer membrane wall of the nanotubes is important to accelerate refolding of the denatured proteins during their transport in the narrow nanotube channels.

Two variables dominating the retention of intact proteins under gradient elution with simultaneous ultrafast high-resolution separation by hydrophobic interaction chromatography

The retention of proteins under gradient elution in HIC is dominated by two variables of steady and migration regions.

Simplified in vitro refolding and purification of recombinant human granulocyte colony stimulating factor using protein folding cation exchange chromatography

Protein folding-strong cation exchange chromatography (PF-SCX) has been employed for efficient refolding with simultaneous purification of recombinant human granulocyte colony stimulating factor (rhG-CSF). To acquire a soluble form of renatured and purified rhG-CSF, various chromatographic conditions, including the mobile phase composition and pH was evaluated. Additionally, the effects of additives such as urea, amino acids, polyols, sugars, oxidizing agents and their amalgamations were also investigated. Under the optimal conditions, rhG-CSF was efficaciously solubilized, refolded and simultaneously purified by SCX in a single step. The experimental results using ribose (2.0M) and arginine (0.6M) combination were found to be satisfactory with mass yield, purity and specific activity of 71%, ≥99% and 2.6×10(8)IU/mg respectively. Through this investigation, we concluded that the SCX refolding method was more efficient than conventional methods which has immense potential for the large-scale production of purified rhG-CSF.

Refolding and simultaneous purification of recombinant human proinsulin from inclusion bodies on protein-folding liquid-chromatography columns

Protein-folding liquid chromatography (PFLC) is an effective and scalable method for protein renaturation with simultaneous purification. However, it has been a challenge to fully refold inclusion bodies in a PFLC column. In this work, refolding with simultaneous purification of recombinant human proinsulin (rhPI) from inclusion bodies from Escherichia coli were investigated using the surface of stationary phases in immobilized metal ion affinity chromatography (IMAC) and high-performance size-exclusion chromatography (HPSEC). The results indicated that both the ligand structure on the surface of the stationary phase and the composition of the mobile phase (elution buffer) influenced refolding of rhPI. Under optimized chromatographic conditions, the mass recoveries of IMAC column and HPSEC column were 77.8 and 56.8% with purifies of 97.6 and 93.7%, respectively. These results also indicated that the IMAC column fails to refold rhPI, and the HPSEC column enables efficient refolding of rhPI with a low-urea gradient-elution method. The refolded rhPI was characterized by circular dichroism spectroscopy. The molecular weight of the converted human insulin was further confirmed with SDS-18% PAGE, Matrix-Assisted Laser Desorption/ Ionization Time of Flight Mass Spectrometry (MALDI-TOF-MS) and the biological activity assay by HP-RPLC.

One-step refolding and purification of recombinant human tumor necrosis factor-α (rhTNF-α) using ion-exchange chromatography

Protein refolding is a key step for the production of recombinant proteins, especially at large scales, and usually their yields are very low. Chromatographic-based protein refolding techniques have proven to be superior to conventional dilution refolding methods. High refolding yield can be achieved using these methods compared with dilution refolding of proteins. In this work, recombinant human tumor necrosis factor-α (rhTNF-α) from inclusion bodies expressed in Escherichia coli was renatured with simultaneous purification by ion exchange chromatography with a DEAE Sepharose FF column. Several chromatographic parameters influencing the refolding yield of the denatured/reduced rhTNF-α, such as the urea concentration, pH value and concentration ratio of glutathione/oxidized glutathione in the mobile phase, were investigated in detail. Under optimal conditions, rhTNF-α can be renatured and purified simultaneously within 30 min by one step. Specific bioactivity of 2.18 × 10(8) IU/mg, purity of 95.2% and mass recovery of 76.8% of refolded rhTNF-α were achieved. Compared with the usual dilution method, the ion exchange chromatography method developed here is simple and more effective for rhTNF-α refolding in terms of specific bioactivity and mass recovery.

The ionic liquid isopropylammonium formate as a mobile phase modifier to improve protein stability during reversed phase liquid chromatography

The room temperature ionic liquid isopropylammonium formate (IPAF) is studied as a reversed phase HPLC mobile phase modifier for separation of native proteins using a polymeric column and the protein stability is compared to that using acetonitrile (MeCN) as the standard organic mobile phase modifier. A variety of important proteins with different numbers of subunits are investigated, including non-subunit proteins: albumin, and amyloglucosidase (AMY); a two subunit protein: thyroglobulin (THY); and four subunit proteins: glutamate dehydrogenase (GDH) and lactate dehydrogenase (LDH). A significant enhancement in protein stability is observed in the chromatograms upon using IPAF as a mobile phase modifier. The first sharper peak at about 2min represented protein in primarily the native form and a second broader peak more retained at about 5-6min represented substantially denatured or possibly aggregated protein. The investigated proteins (except LDH) could maintain the native form within up to 50% IPAF, while a mobile phase, with as low as 10% MeCN, induced protein denaturation. The assay for pyruvate using LDH has further shown that enzymatic activity can be maintained up to 30% IPAF in water in contrast to no activity using 30% MeCN.

WITHDRAWN: Smart polymer-coated microplate wells: Applications in protein purification, protein refolding, and sensing of analytes

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Fast preparation of recombinant human stem cell factor from inclusion bodies using different hydrophobic interaction chromatographic columns

A method was developed to increase the recovery of recombinant human stem cell factor (rhSCF) from inclusion bodies using high performance hydrophobic interaction chromatography (HPHIC). The target protein was first solubilized in 8.0 mol/L urea solution, and was purified and refolded simultaneously by HPHIC with different chromatographic cakes. Experimental conditions, such as the ligand structures of stationary phase and the composition of mobile phase, were optimized. Under the optimal conditions, high mass recoveries and specific activities of rhSCF were acquired, the purities of rhSCF were above 95.5%, and the mass recoveries of rhSCF were above 49.6%. The final product was also verified as monomer by size exclusion chromatography and matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS). These results provided further evidence that HPHIC is an effective tool in the refolding and purification of recombinant proteins.

Soft nanotube hydrogels functioning as artificial chaperones

Self-assembly of rationally designed asymmetric amphiphilic monomers in water produced nanotube hydrogels in the presence of chemically denatured proteins (green fluorescent protein, carbonic anhydrase, and citrate synthase) at room temperature, which were able to encapsulate the proteins in the one-dimensional channel of the nanotube consisting of a monolayer membrane. Decreasing the concentrations of the denaturants induced refolding of part of the encapsulated proteins in the nanotube channel. Changing the pH dramatically reduced electrostatic attraction between the inner surface mainly covered with amino groups of the nanotube channel and the encapsulated proteins. As a result, the refolded proteins were smoothly released into the bulk solution without specific additive agents. This recovery procedure also transformed the encapsulated proteins from an intermediately refolding state to a completely refolded state. Thus, the nanotube hydrogels assisted the refolding of the denatured proteins and acted as artificial chaperones. Introduction of hydrophobic sites such as a benzyloxycarbony group and a tert-butoxycarbonyl group onto the inner surface of the nanotube channels remarkably enhanced the encapsulation and refolding efficiencies based on the hydrophobic interactions between the groups and the surface-exposed hydrophobic amino acid residues of the intermediates in the refolding process. Refolding was strongly dependent on the inner diameters of the nanotube channels. Supramolecular nanotechnology allowed us to not only precisely control the diameters of the nanotube channels but also functionalize their surfaces, enabling us to fine-tune the biocompatibility. Hence, these nanotube hydrogel systems should be widely applicable to various target proteins of different molecular weights, charges, and conformations.

High pH solubilization and chromatography-based renaturation and purification of recombinant human granulocyte colony-stimulating factor from inclusion bodies

Recombinant human granulocyte colony-stimulating factor (rhG-CSF) is a very efficient therapeutic protein drug which has been widely used in human clinics to treat cancer patients suffering from chemotherapy-induced neutropenia. In this study, rhG-CSF was solubilized from inclusion bodies by using a high-pH solution containing low concentration of urea. It was found that solubilization of the rhG-CSF inclusion bodies greatly depended on the buffer pH employed; alkalic pH significantly favored the solubilization. In addition, when small amount of urea was added to the solution at high pH, the solubilization was further enhanced. After solubilization, the rhG-CSF was renatured with simultaneous purification by using weak anion exchange, strong anion exchange, and hydrophobic interaction chromatography, separately. The results indicated that the rhG-CSF solubilized by the high-pH solution containing low concentration of urea had much higher mass recovery than the one solubilized by 8 M urea when using anyone of the three refolding methods employed in this work. In the case of weak anion exchange chromatography, the high pH solubilized rhG-CSF could get a mass recovery of 73%. The strategy of combining solubilization of inclusion bodies at high pH with refolding of protein using liquid chromatography may become a routine method for protein production from inclusion bodies.

Role of α-helical structure in organic solvent-activated homodimer of elastase strain K

Recombinant elastase strain K overexpressed from E. coli KRX/pCon2(3) was purified to homogeneity by a combination of hydrophobic interaction chromatography and ion exchange chromatography, with a final yield of 48% and a 25-fold increase in specific activity. The purified protein had exhibited a first ever reported homodimer size of 65 kDa by SDS-PAGE and MALDI-TOF, a size which is totally distinct from that of typically reported 33 kDa monomer from P. aeruginosa. The organic solvent stability experiment had demonstrated a stability pattern which completely opposed the rules laid out in previous reports in which activity stability and enhancement were observed in hydrophilic organic solvents such as DMSO, methanol, ethanol and 1-propanol. The high stability and enhancement of the enzyme in hydrophilic solvents were explained from the view of alteration in secondary structures. Elastinolytic activation and stability were observed in 25 and 50% of methanol, respectively, despite slight reduction in α-helical structure caused upon the addition of the solvent. Further characterization experiments had postulated great stability and enhancement of elastase strain K in broad range of temperatures, pHs, metal ions, surfactants, denaturing agents and substrate specificity, indicating its potential application in detergent formulation.

Protein folding liquid chromatography

A method for carrying out protein folding with simultaneous separation by protein folding liquid chromatography (PFLC) is described herein. Furthermore, a two-dimensional chromatographic column, termed a 2D column, which can be independently employed for accomplishing PFLC in either weak cation exchange mode or hydrophobic interaction chromatography mode is reported. The content of this chapter describes the most commonly employed methods and operations of PFLC, such as the use of urea or guanidine hydrochloride as a denaturant with the protein in either the reduced or oxidized state and solving problems caused by the formation of the precipitates during protein folding. The PFLC can be performed using conventional chromatographic columns and a new chromatographic cake. A protocol for fast renaturation with simultaneous purification of inclusion body protein of the recombinant human interferon-gamma to obtain purity ≥95% and high specific bioactivity in a single step and in 1 h is introduced.

Refolding of denatured/reduced lysozyme at high concentrations by artificial molecular chaperone-ion exchange chromatography

Development of high efficiency and low cost protein refolding methods is a highlighted research focus in biotechnology. Artificial molecular chaperone (AMC) and protein folding liquid chromatography (PFLC) are two attractive refolding methods developed in recent years. In the present work, AMC and one branch of PFLC, ion exchange chromatography (IEC), are integrated to form a new refolding method, artificial molecular chaperone-ion exchange chromatography (AMC-IEC). This new method is applied to the refolding of a widely used model protein, urea-denatured/dithiothreitol-reduced lysozyme. Many factors influencing the refolding of lysozyme, such as urea concentration, beta-cyclodextrin concentration, molar ratio of detergent to protein, mobile phase flow rate, and type of detergent, were investigated, respectively, to optimize the conditions for lysozyme refolding by AMC-IEC. Compared with normal IEC refolding method, the activity recoveries of lysozyme obtained by AMC-IEC were much higher in the investigated range of initial protein concentrations. Moreover, the activity recoveries obtained by using this newly developed refolding method were still quite high for denatured/reduced lysozyme at high initial concentrations. When the initial protein concentration was 200 mg mL(-1), the activity recovery was over 60%. In addition, the lifetime of the chromatographic column during AMC-IEC was much longer than that during protein refolding by normal IEC. Therefore, AMC-IEC is a high efficient and low cost protein refolding method.

A new approach for characterizing the intermediate feature of α-chymotrypsin refolding by hydrophobic interaction chromatography

A new approach for characterizing the intermediate of urea-denatured α-chymotrypsin (α-Chy) by hydrophobic interaction chromatography (HIC) is presented. The contact surface region (Z, S), affinity (logI), and the character of interaction force (j) of the α-Chy to the stationary phase of HIC (STHIC) between the intermediate (M) and native (N) states were found to be quite different as urea concentration (C_urea) changes. With the changes in C_urea, a linear relationship between logI and Z was found to exist only for its N state, not for M state, indicating the interaction force between α-Chy in N state to the STHIC to be non-selective, but selective one for its M state. Also, the measured magnitude of both logI and Z in M state is only a fifth of that in N state. All three parameters were employed to distinguish protein in the N state from that in the M state. It would be expected that this result could be employed to distinguish any kind of non-functional protein having correct three-, or four-dimensional molecular structure from their stable M state of any kinds of proteins, and/or other proteins in proteome investigation, separation process of protein, and intensively understanding the intrinsic rule of protein folding in molecular biology.

Solubilization and refolding with simultaneous purification of recombinant human stem cell factor

Recombinant human stem cell factor (rhSCF) was solubilized and renatured from inclusion bodies expressed in Escherichia coli. The effect of both pH and urea on the solubilization of rhSCF inclusion bodies was investigated; the results indicate that the solubilization of rhSCF inclusion bodies was significantly influenced by the pH of the solution employed, and low concentration of urea can drastically improve the solubilization of rhSCF when solubilized by high pH solution. The solubilized rhSCF can be easily refolded with simultaneous purification by ion exchange chromatography (IEC), with a specific activity of 7.8 x 10(5) IU x mg(-1), a purity of 96.3%, and a mass recovery of 43.0%. The presented experimental results show that rhSCF solubilized by high pH solution containing low concentration of urea is easier to be renatured than that solubilized by high concentration of urea, and the IEC refolding method was more efficient than dilution refolding and dialysis refolding for rhSCF. It may have a great potential for large-scale production of rhSCF.