Production scale purification of biosynthetic human insulin by reversed-phase high-performance liquid chromatography

Conversion of mammalian cell culture media waste to microbial fermentation feed efficiently supports production of recombinant protein by Escherichia coli

Deriving new value from waste streams through secondary processes is a central aim of the circular bioeconomy. In this study we investigate whether chemically defined spent media (CDSM) waste from cell culture bioprocess can be recycled and used as a feed in secondary microbial fermentation to produce new recombinant protein products. Our results show that CDSM supplemented with 2% glycerol supported a specific growth rate of E. coli cultures equivalent to that achieved using a nutritionally rich microbiological media (LB). The titre of recombinant protein produced following induction in a 4-hour expression screen was approximately equivalent in the CDSM fed cultures to that of baseline, and this was maintained in a 16-hr preparative fermentation. To understand the protein production achieved in CDSM fed culture we performed a quantitative analysis of proteome changes in the E. coli using mass spectrometry. This analysis revealed significant upregulation of protein synthesis machinery enzymes and significant downregulation of carbohydrate metabolism enzymes. We conclude that spent cell culture media, which represents 100s of millions of litres of waste generated by the bioprocessing industry annually, may be valorized as a feed resource for the production of recombinant proteins in secondary microbial fermentations. Data is available via ProteomeXchange with identifier PXD026884.

New and efficient purification process for recombinant human insulin produced in Escherichia coli

A new and efficient purification process for recombinant human insulin production was developed by exploring new resins and optimizing purification steps from E. coli inclusion body washing to insulin polishing. A combined additives inclusion body wash protocol drastically improved efficiency in clarifying ZZ-proinsulin samples. ZZ-proinsulin recovery increased three-fold under optimized solubilization and sulfitolysis incubation temperature and duration. Desalting with Bio-Gel P4 and P6 resulted in higher sample loading and product recovery compared to conventional resins. A higher recovery (96%) and purity (81%) of ZZ-proinsulin were achievable with the Nuvia S cation exchanger for proinsulin purification compared to a reported process using expensive affinity chromatography resin. As the first step for insulin purification, process scale-up is more economical and practical when Nuvia HR-S cation exchanger was used instead of commonly used reversed-phase chromatography. Nuvia HR-S was highly effective in removing ZZ fusion protein (90% removal) after enzymatic cleavage, although ZZ fusion protein has a very close theoretical pI to human insulin, which was supposedly challenging to be removed by cation exchange chromatography. Also, insulin can be eluted at a lower ethanol % using Nuvia HR-S compared to other reported processes and is thus more environmentally sustainable. Recombinant human insulin was obtained with over 98% purity in just a single reversed-phase polishing step, which is comparable to the reference standard. The process workflow presented here can be potentially applied for the development of purification workflow for insulin analogs or other peptide products derived from E. coli inclusion body.Key points• Drastic efficiency improvement for inclusion body wash with combined additives.• High recovery of proinsulin purification with high capacity cation exchange resin.• Effective removal of fusion tag at lower ethanol % with high-resolution resin.

Downstream processing of recombinant human insulin and its analogues production from E. coli inclusion bodies

The Global Diabetes Compact was launched by the World Health Organization in April 2021 with one of its important goals to increase the accessibility and affordability of life-saving medicine-insulin. The rising prevalence of diabetes worldwide is bound to escalate the demand for recombinant insulin therapeutics, and currently, the majority of recombinant insulin therapeutics are produced from E. coli inclusion bodies. Here, a comprehensive review of downstream processing of recombinant human insulin/analogue production from E. coli inclusion bodies is presented. All the critical aspects of downstream processing, starting from proinsulin recovery from inclusion bodies, inclusion body washing, inclusion body solubilization and oxidative sulfitolysis, cyanogen bromide cleavage, buffer exchange, purification by chromatography, pH precipitation and zinc crystallization methods, proinsulin refolding, enzymatic cleavage, and formulation, are explained in this review. Pertinent examples are summarized and the practical aspects of integrating every procedure into a multimodal purification scheme are critically discussed. In the face of increasing global demand for insulin product, there is a pressing need to develop a more efficient and economical production process. The information presented would be insightful to all the manufacturers and stakeholders for the production of human insulins, insulin analogues or biosimilars, as they strive to make further progresses in therapeutic recombinant insulin development and production.

High-Performance Reversed-Phase Flash Chromatography Purification of Peptides and Chemically Modified Insulins

Preparative reversed-phase HPLC is the established method for the purification of peptides, but has significant limitations. We systematically investigated the use of high-performance reversed-phase flash chromatography (HPFC) to rapidly purify laboratory-scale quantities of crude, synthetic peptides and chemically modified insulins. We demonstrated these methods for a diverse set of peptides, including short, medium, and long peptides. Depending on the purity profile of the peptide, HPFC can be used either as the sole purification method, or as a pre-purification method prior to final HPLC purification. Furthermore, HPFC is suitable for the purification of peptides that are not fully in solution. We provide guidelines for the HPFC of synthetic peptides and small proteins, including the choice of columns, eluents, and gradients. We believe that HPFC is a valuable alternative to HPLC purification of peptides and small proteins.

A novel and more efficient biosynthesis approach for human insulin production in Escherichia coli (E. coli)

Insulin has captured researchers' attention worldwide. There is a rapid global rise in the number of diabetic patients, which increases the demand for insulin. Current methods of insulin production are expensive and time-consuming. A PCR-based strategy was employed for the cloning and verification of human insulin. The human insulin protein was then overexpressed in E. coli on a laboratory scale. Thereafter, optimisation of human insulin expression was conducted. The yield of human insulin produced was approximately 520.92 (mg/L), located in the intracellular fraction. Human insulin was detected using the MALDI-TOF-MS and LC-MS methods. The crude biosynthesised protein sequence was verified using protein sequencing, which had a 100% similarity to the human insulin sequence. The biological activity of human insulin was tested in vitro using a MTT assay, which revealed that the crude biosynthesised human insulin displayed a similar degree of efficacy to the standard human insulin. This study eliminated the use of affinity tags since an untagged pET21b expression vector was employed. Tedious protein renaturation, inclusion body recovery steps, and the expensive enzymatic cleavage of the C-peptide of insulin were eliminated, thereby making this method of biosynthesising human insulin a novel and more efficient method.

Identification of Lysine Misincorporation at Asparagine Position in Recombinant Insulin Analogs Produced in E. coli

PURPOSE

Identification of human insulin analogs' impurity with a mass shift +14 Da in comparison to a parent protein.

METHODS

The protein sequence variant was detected and identified with the application of peptide mapping, liquid chromatography, tandem mass spectrometric analysis, nuclear magnetic resonance spectroscopy (NMR) and Edman sequencing.

RESULTS

The misincorporated lysine (Lys) at asparagine (Asn) position A21 was detected in recombinant human insulin and its analogs.

CONCLUSIONS

Although there are three asparagine residues in the insulin derivative, the misincorporation of lysine occurred only at position A21. The process involves G/U or A/U wobble base pairing.

Total Chemical Synthesis of an Intra-A-Chain Cystathionine Human Insulin Analogue with Enhanced Thermal Stability

Despite recent advances in the treatment of diabetes mellitus, storage of insulin formulations at 4 °C is still necessary to minimize chemical degradation. This is problematic in tropical regions where reliable refrigeration is not ubiquitous. Some degradation byproducts are caused by disulfide shuffling of cystine that leads to covalently bonded oligomers. Consequently we examined the utility of the non-reducible cystine isostere, cystathionine, within the A-chain. Reported herein is an efficient method for forming this mimic using simple monomeric building blocks. The intra-A-chain cystathionine insulin analogue was obtained in good overall yield, chemically characterized and demonstrated to possess native binding affinity for the insulin receptor isoform B. It was also shown to possess significantly enhanced thermal stability indicating potential application to next-generation insulin analogues.

Biotechnology and genetic engineering in the new drug development. Part I. DNA technology and recombinant proteins

Pharmaceutical biotechnology has a long tradition and is rooted in the last century, first exemplified by penicillin and streptomycin as low molecular weight biosynthetic compounds. Today, pharmaceutical biotechnology still has its fundamentals in fermentation and bioprocessing, but the paradigmatic change affected by biotechnology and pharmaceutical sciences has led to an updated definition. The biotechnology revolution redrew the research, development, production and even marketing processes of drugs. Powerful new instruments and biotechnology related scientific disciplines (genomics, proteomics) make it possible to examine and exploit the behavior of proteins and molecules. Recombinant DNA (rDNA) technologies (genetic, protein, and metabolic engineering) allow the production of a wide range of peptides, proteins, and biochemicals from naturally nonproducing cells. This technology, now approximately 25 years old, is becoming one of the most important technologies developed in the 20(th) century. Pharmaceutical products and industrial enzymes were the first biotech products on the world market made by means of rDNA. Despite important advances regarding rDNA applications in mammalian cells, yeasts still represent attractive hosts for the production of heterologous proteins. In this review we describe these processes.

Insulin related compounds and identification

Insulin-related compounds (IRCs), which originate during the expression and purification of human insulin using recombinant Escherichia coli, were purified and identified. We investigated the identity of IRCs and their origin. We also presented methods for inhibiting IRC formation. The strains used in this report were E. coli B5K and E. coli H27R. E. coli B5K had a 6-amino acid-fused peptide at the N-terminus of proinsulin, and E. coli H27R had a 28-amino acid-fused peptide at the N-terminus of proinsulin. We investigated the identity of IRCs and their origin by mainly using High Performance Liquid Chromatography (HPLC). The well-known IRCs, desamido human insulin and desthreonine human insulin, formed in both strains. In addition to these two IRCs, the B5K strain produced three different IRCs, Arg(A(0))-insulin (IRC 1), prepeptide-insulin (IRC 2), and Glu(A(22))-insulin (IRC 3). The amounts of IRC 1, IRC 2, IRC 3 were approximately 0.1-0.3% after final purification step. Among these IRCs, Arg(A(0))-insulin, prepeptide-insulin, and desthreonine insulin originated from incomplete enzyme reaction. Glu(A(22))-insulin was formed when we used a double stop codon during the expression of preproinsulin; that is, it was formed by the misreading of the first stop codon through the amber mutation. The major IRCs of the H27R strain were human insulin fragment (B1-B21) (IRC 4), and A9(Ser→Asn) amino acid single mutation human insulin (IRC 5), Arg(B(31))-insulin (IRC 6). Human insulin fragment (B1-B21) was formed by β-mercaptoethanol, which was added during refolding. It formed when the disulfide bonds between A-chain and B-chain of human insulin were cut by β-mercaptoethanol, followed by cleavage of the B-chain by trypsin and carboxypeptidase B. A9(Ser→Asn) amino acid single mutation human insulin originated from the mistranslation of A9 serine, such that asparagine was translated instead of serine. Arg(B(31))-insulin originated from incomplete enzyme reaction. The amount of IRC 4 was 10-15% after enzyme reaction. The amounts of IRC 5, IRC 6 were around 0.2% after final purification step. We present methods for inhibiting the formation of IRCs by controlling the amount of enzyme, controlling the rate of enzyme reaction, using a single stop codon, using hydrogen peroxide (H(2)O(2)) to inhibit β-mercaptoethanol, and modifying the A9 codon.

Computer-aided process analysis and economic evaluation for biosynthetic human insulin production-A case study

Human insulin was the first mammalian protein produced in bacteria using recombinant DNA technology. Two technologies were developed; the first based on the separate expression of precursors of chains A and B of insulin, and the second based on the expression of a precursor of proinsulin as a Trp-E fusion protein. Both technologies utilized Escherichia coli as an expression system. Later, a third technology was developed based on a strain of yeast that can secrete a precursor of insulin. The second E. coli process, a variation of which has been commercialized by Eli Lilly and Co., is analyzed in this article from a process design and economic evaluation viewpoint. The objective of this work is to elucidate the technical complexity and high cost associated with the manufacturing of biopharmaceuticals. Human insulin is a good example of a protein-based biopharmaceutical produced in large quantities (a fex tons per year) that requires large scale equipment and presents a multitude of scale-up challenges. Based onthe analysis, a number of conclusions are drawn regarding the cost breakdown and cost dependency on process parameters. Recommendations are made for cost reduction and environmental impact minimization. This analysis was performed using a software tool for computer-aided bioprocess design. (c) 1995 John Wiley & Sons, Inc.

Enantioseparation of omeprazole--effect of different packing particle size on productivity

Enantiomeric separation of omeprazole has been extensively studied regarding both product analysis and preparation using several different chiral stationary phases. In this study, the preparative chiral separation of omeprazole is optimized for productivity using three different columns packed with amylose tris (3,5-dimethyl phenyl carbamate) coated macroporous silica (5, 10 and 25 μm) with a maximum allowed pressure drop ranging from 50 to 400 bar. This pressure range both covers low pressure process systems (50-100 bar) and investigates the potential for allowing higher pressure limits in preparative applications in a future. The process optimization clearly show that the larger 25 μm packing material show higher productivity at low pressure drops whereas with increasing pressure drops the smaller packing materials have substantially higher productivity. Interestingly, at all pressure drops, the smaller packing material result in lower solvent consumption (L solvent/kg product); the higher the accepted pressure drop, the larger the gain in reduced solvent consumption. The experimental adsorption isotherms were not identical for the different packing material sizes; therefore all calculations were recalculated and reevaluated assuming identical adsorption isotherms (with the 10 μm isotherm as reference) which confirmed the trends regarding productivity and solvent consumption.

Evaluating the conformation of recombinant domain I of β(2)-glycoprotein I and its interaction with human monoclonal antibodies

Pathogenic antiphospholipid antibodies (aPL) cause the antiphospholipid syndrome (APS) by interacting with domain I (DI) of beta-2-glycoprotein I (β₂GPI). The aPL/β₂GPI complex then exerts pathogenic effects on target cells. We previously described periplasmic bacterial expression of native and mutated variants of DI, and reported the presence of immunodominant epitopes at positions 8–9 (D8/D9) and position 39 (R39). Mutations at these positions strongly influenced the ability of recombinant DI to bind patient-derived IgG aPL and to inhibit pathogenic effects of these aPL in a mouse model of APS.

We now describe an improved cytoplasmic bacterial expression system allowing higher yield of DI. We demonstrate that the nuclear magnetic resonance (NMR) spectra of a ¹⁵N,¹³C-isotope-labelled sample of the recombinant DI protein exhibit properties consistent with the structure of DI in crystal structure of intact β₂GPI. Mutations at D8/D9 and R39 had limited impact on the NMR spectrum of DI indicating maintenance of the overall fold of the DI domain.

We investigated interactions between five variants of DI and ten monoclonal human IgG antibodies, all derived from the IgG aPL antibody IS4 by sequence manipulation and in vitro expression. Arginine residues at positions 100 and 100g in IS4V_H CDR3 play a particularly important role in binding to DI, but this is unlikely to be due to electrostatic interactions with negatively charged amino acids on DI. Both the strength of binding to DI and the ability to discriminate different DI variants varies between the different IgG antibodies tested. There was no simple relationship between these binding properties and antibody pathogenicity.

In vitro folding of methionine-arginine human lyspro-proinsulin S-sulfonate-disulfide formation pathways and factors controlling yield

We investigated the in vitro folding of an oxidized proinsulin (methionine-arginine human lyspro-proinsulin S-sulfonate), using cysteine as a reducing agent at 5°C and high pH (10.5-11). Folding intermediates were detected and characterized by means of matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), reversed-phase chromatography (RPC), size-exclusion chromatography, and gel electrophoresis. The folding kinetics and yield depended on the protein and cysteine concentrations. RPC coupled with MALDI-MS analyses indicated a sequential formation of intermediates with one, two, and three disulfide bonds. The MALDI-MS analysis of Glu-C digested, purified intermediates indicated that an intra-A-chain disulfide bond formed first among A6, A7, and A11. Various non-native intra-A (A20 with A6, A7, or A11), intra-B (between B7 and B19), and inter-A-B disulfide bonds were observed in the intermediates with two disulfide bonds. The intermediates with three disulfide bonds had mainly the non-native intra-A and intra-B bonds. At a cysteine-to-proinsulin-SH ratio of 3.5, all intermediates with the non-native disulfide bonds were converted to properly folded proinsulin via disulfide bond reshuffling, which was the slowest step. Aggregation via the formation of intermolecular disulfide bonds of early intermediates was the major cause of yield loss. At a higher cysteine-to-proinsulin-SH ratio, some intermediates and folded MR-KPB-hPI were reduced to proteins with thiolate anions, which caused unfolding and even more yield loss than what resulted from aggregation of the early intermediates. Reducing protein concentration, while keeping an optimal cysteine-to-protein ratio, can improve folding yield significantly.

Phenomena of insulin peak fronting in size exclusion chromatography and strategies to reduce fronting

Insulin peak fronting in size exclusion chromatography (SEC) results in more than 10% yield loss in the production of insulin. The goal of this study is to understand the mechanisms of peak fronting and to develop strategies to reduce fronting and increase insulin yield. Chromatography experiments ruled out pressure surge, viscous fingering, and adsorption as the cause for peak fronting. Theoretical analysis based on a general rate model indicated that reversible dimerization is the major cause for peak fronting and reducing the dimerization equilibrium constant is the most effective method for reducing fronting. Two strategies were developed and tested to reduce the degree of dimer formation. The first strategy was to use 0.1N acetic acid as the presaturant and eluent. The second strategy was to use 0.8 or 2.8N acetic acid in 20vol.% denatured ethanol as the mobile phase. The experimental results showed that both strategies can reduce insulin peak fronting in SEC, maintain desired product purity, and increase insulin yield to higher than 98%.

Practical reversed-phase high-performance liquid chromatography method for laboratory-scale purification of recombinant human thyrotropin

A small, semi-preparative C(4) RP-HPLC column was used to set up the conclusive laboratory-scale purification of Chinese hamster ovary-derived human thyrotropin (hTSH), after a preliminary concentration-purification of an extremely dilute and poorly ( approximately 0.6 microg hTSH/mL; mass fraction=0.35%) conditioned medium on a cation exchanger. Several fractions of this eluate were repeatedly injected on the semi-preparative column, obtaining, in a single run (<1h chromatographic time), a concentrated pool ( approximately 1.2 mg/mL) of highly purified hTSH that could be further concentrated to >3 mg/mL and then efficiently lyophilized. The overall recovery in the rapid RP-HPLC purification step, including concentration and lyophilization, was of the order of 80%. The final product, when tested via a precise, single-dose in vivo bioassay, confirmed that it did not suffer any loss of bioactivity. This same methodology can be easily adapted to the small-scale purification of other recombinant products, even when obtained from genetically modified organisms at extremely low concentrations and mass fractions.

Optimization of silica-based media for antibody purification by protein A affinity chromatography

Considering the large molecular size of IgG antibodies widely used for therapeutic applications, the pore size, pore volume and coupling density of silica-based media were optimized for the effective large-scale purification, using an antibody-protein A affinity system. Silica media, with average pore sizes from 70 nm to 140 nm and surface areas of 26-67 m(2)/g, were prepared and coupled with protein A. The static adsorption capacity and dynamic binding capacity of bovine and human IgG were measured at superficial liquid velocities ranging from 94 to 720 cm/h. The volumetric coefficient of mass transfer of the alkali-treated silica-based protein A media, with a pore size of 110 nm, was four times higher than the values for cross-linked agarose media and thus had high dynamic binding capacities at high superficial liquid velocities.

Process and purification for manufacture of a modified insulin intended for oral delivery

Oral delivery of insulin is convenient and physiologically desirable in the treatment of diabetes. However, this route of administration has presented substantial challenges as insulin is degraded enzymatically in the gut, resulting in low bioavailability. We have developed a conjugated insulin product (IN-105) that has high bioavailability and is currently undergoing clinical trials for the treatment of diabetes. A process for the manufacture of IN-105 was developed. Initially, recombinant human insulin was conjugated covalently with a monodisperse, short-chain methoxypolyethylene glycol derivative. The desired product, IN-105, was purified from its closely related species using RP-HPLC and cation exchange chromatography to a purity of 98.5%. The elution pool from cation exchange chromatography was crystallized and lyophilized into the dry active pharmaceutical ingredient.

Methods for protecting silica sorbents used in high-performance liquid chromatography from strongly adsorbed impurities during purification of human recombinant insulin

One of the main stages of human recombinant insulin (HRI) production is the hormone purification by means of reversed phase high-performance liquid chromatography (RP HPLC). The optimization of this stage determines the increase of the total manufacturing yield. Therefore, the cost of the sorbent used in HPLC influences the cost of the manufacturing product, i.e. HRI substance. However, resolution between HRI and its admixtures decreases with time. The reason for this is the sorbent contamination with strongly adsorbed impurities (SAI) which are accumulated during elution. In the following research several methods for sorbent protection are studied. The opinion that SAI are mainly high-molecular weight compounds was examined using gel filtration. Different sorbent types were tested for the use in guard column. The results obtained were applied and improved at preparative level.

Single-Molecule Probing of Adsorption and Diffusion on Silica Surfaces

Single-molecule spectroscopy has emerged as a valuable tool in probing kinetics and dynamic equilibria in adsorption because advances in instrumentation and technology have enabled researchers to obtain high signal-to-noise ratios for common dyes at room temperature. Single-molecule spectroscopy was applied to the study of an important problem in chromatography: peak broadening and asymmetry in the chromatograms of pharmaceuticals, peptides, and proteins. Using DiI, a cationic dye that exhibits the same problematic chromatographic behavior, investigators showed that the adsorption sites that cause chromatographic problems are located at defects on the silica crystal surface.

Human insulin and desamido human insulin isotherms in ethanol–water reversed phase systems

The multi-component isotherms for human insulin (HI) and desamido human insulin (dHI) over reversed phase packing (C18) and with 29.8% (w/w) ethanol-water as mobile phase have been determined experimentally. The isotherms of HI in ethanol-water differ from those obtained with the more commonly applied methanol-water and acetonitrile-water mobile phase, as described in this paper. The isotherm exhibits anti Langmuirian behavior and can be very well modeled by an anti Langmuir isotherm presented in this paper. The HI and dHI anti Langmuir isotherm are determined as: qHI = (8.4C(HI) + 3C(HI)CdHI)/(1 - 0.05C(HI) - 0.14CdHI + 0.04C(HI)CdHI) and qdHI = (11.4CdHI + 2C(HI)CdHI)/ (1 - 0.05C(HI) - 0.14CdHI + 0.04C(HI)CdHI)

Bioprocessing of therapeutic proteins from the inclusion bodies of Escherichia coli

Escherichia coli has been most extensively used for the large-scale production of therapeutic proteins, which do not require complex glycosylation for bioactivity. In recent years tremendous progress has been made on the molecular biology, fermentation process development and protein refolding from inclusion bodies for efficient production of therapeutic proteins using E. coli. High cell density fermentation and high throughput purification of the recombinant protein from inclusion bodies of E. coli are the two major bottle necks for the cost effective production of therapeutic proteins. The aim of this review is to summarize the developments both in high cell density, high productive fermentation and inclusion body protein refolding processes using E. coli as an expression system. The first section deals with the problems of high cell density fermentation with an aim to high volumetric productivity of recombinant protein. Process engineering parameters during the expression of ovine growth hormone as inclusion body in E. coli were analyzed. Ovine growth hormone yield was improved from 60 mg L(-1) to 3.2 g L(-1) using fed-batch culture. Similar high volumetric yields were also achieved for human growth hormone and for recombinant bonnet monkey zona pellucida glycoprotein expressed as inclusion bodies in E. coli. The second section deals with purification and refolding of recombinant proteins from the inclusion bodies of E. coli. The nature of inclusion body protein, its characterization and isolation from E. coli has been discussed in detail. Different solubilization and refolding methods, which have been used to recover bioactive protein from inclusion bodies of E. coli have also been discussed. A novel inclusion body protein solubilization method, while retaining the existing native-like secondary structure of the protein and its subsequent refolding in to bioactive form, has been discussed. This inclusion body solubilization and refolding method has been applied to recover bioactive recombinant ovine growth hormone, recombinant human growth hormone and bonnet monkey zona pellucida glycoprotein from the inclusion bodies of E. coli.

Aprotinin conformational distributions during reversed-phase liquid chromatography. Analysis by hydrogen-exchange mass spectrometry

Hydrogen-exchange mass spectrometry analysis of the stable protein aprotinin during reversed-phase liquid chromatography shows both native and unfolded protein. The behavior is consistent with only two conformational states, a near-native state and a fully solvent-accessible state, with reversible interchange of species within and between the mobile and stationary phases. The amount of unfolded form is greater on C18 relative to C4 alkyl modified silica surfaces. The addition of (NH4)2SO4, Na2SO4, NaCl, or NaSCN to the mobile phase stabilized native conformation on the chromatographic surface, especially on the C4 media. Finally, the retention and the proportion of denatured form increases with added salts in anorder consistent with the lyotropic series, but reversed from that observed for small molecules.

On-line SPE-RP-LC for the determination of insulin derivatives in biological matrices

An automated and on-line solid-phase extraction (SPE)-liquid chromatography (LC) procedure is described for the determination of insulin in biological matrices. The total procedure consists of two SPEs in series, followed by RP-LC separation. During the first SPE a strong anion-exchange (SAX) cartridge (ISOLUTE, 40-90 microm, 10 x 4 mm i.d.) is used, followed by a RP-cartridge (Luna C(8), 4 x 2.0 mm i.d.). The second SPE cartridge contains the same material as the LC column and is used to transfer the sample from the SAX cartridge to the LC column. The developed system can detect 100 nmol/l insulin in aqueous samples and 200 nmol/l insulin in spiked plasma samples using UV. When electrospray ionization (ESI)-mass spectrometry (MS), was coupled with the developed system, the LODs were lowered by a factor two to 50 and 100 nmol/l for aqueous and spiked plasma samples, respectively.

High-level expression and rapid purification of rare-codon genes from hyperthermophilic archaea by the GST gene fusion system

In this study, we compared two gene fusion expression strategies using two rare codon genes (Ssh10b and MtGrxM) from archaea as a model system. Both genes can be highly expressed as N- or C-terminal fusion partners to GST or the intein/chitin-binding tag. However, the fusion protein with intein tag could not be cleaved, even under stringent conditions, possibly due to steric hindrance, thus preventing further purification. In contrast, the GST fusion system could increase protein expression level and the corresponding fusion protein could be easily cleaved by thrombin. After binding to glutathione sepharose, the fusion protein was cleaved on column, and a roughly purified protein fraction was eluted. This fraction was purified by heating at 80 degrees C for 10 min, followed by centrifugation. The correct total mass and N-terminal primary structure were confirmed by mass spectrometry and Edman degradation. Both constructs were used for in vitro expression, and similar results were obtained, indicating higher expression levels of the GST tag vs. intein/chitin tag. Taken together, our results suggest that the GST fusion system can be used as a considerable alternative to synthetic genes for the expression of rare codon genes. The affinity chromatography purification followed by a heating step is an efficient and convenient method for thermostable protein purification.

Distribution of macropores in silica particles prepared by using multiple emulsions

The distribution of macropores in silica particles prepared by the hydrolysis and condensation of TEOS in a hexane/water/decyl alcohol (O(1)/W/O(2)) multiple emulsion was investigated. To stabilize the emulsion structure, hydroxypropyl cellulose (HPC) was added into the O(2) phase and polyethylene glycol (PEG) was added into the water phase. Without HPC, the particles have an irregular shape and hardly have particulate forms. As the concentration of HPC increases, the shape of particles becomes more and more spherical and the size decreases. The size of silica particles was varied from 5 to 1 microm as the concentration of HPC increased from 0.5 to 0.7 wt%. The number and size of the macropores in silica particles were affected by PEG polymer concentration. With the variation in the concentration of PEG, macropores in silica particles were located at the surface of or inside the particles. At high concentrations of PEG, the macropores in particles were located inside the particles, but at low concentrations of PEG the macropores were located at the surfaces of particles. Interestingly, the particles of dimpled surfaces were formed when the molar ratio of water to TEOS (R(w)) was 4.0 and the concentrations of PEG and HPC were 2.0 and 0.7 wt% respectively. The surface areas of dimpled silica particles and completely spherical particles, measured by the BET method, were 409 and 433 m(2)/g respectively.

Advances in Escherichia coli production of therapeutic proteins

Escherichia coli offers a means for the rapid and economical production of recombinant proteins. These advantages, coupled with a wealth of biochemical and genetic knowledge, have enabled the production of such economically sensitive products as insulin and bovine growth hormone. Although significant progress has been made in transcription, translation and secretion, one of the major challenges is obtaining the product in a soluble and bioactive form. Recent progress in oxidative cytoplasmic folding and cell-free protein synthesis offers attractive alternatives to standard expression methods.

Monitoring of recombinant human insulin production by narrow-bore reversed-phase high-performance liquid chromatography, high-performance capillary electrophoresis and matrix-assisted laser desorption ionisation time-of-flight mass spectrometry

An analytical scheme for monitoring recombinant human insulin (rhI) production is suggested. The scheme includes high-performance separation micro-techniques (narrow-bore RP-HPLC, HPCE) based on different separation mechanisms and matrix-assisted laser desorption ionisation time-of-flight MS, and allows one to obtain unambiguous information about purity and primary structure of all intermediates of the rhI production. The use of this scheme at all production steps provided optimisation of certain technological parameters [conditions for a fusion protein (FP) refolding, temperature and duration of the FP cleavage with trypsin, conditions for carboxypeptidase B digestion of di-ArgB31-B32-insulin] and achievement of a high purity of the end-product. The proposed scheme may be used for solving various problems in monitoring production of other recombinant proteins.

Hydrophobic displacement chromatography of proteins

Displacement chromatography of proteins was successfully carried out in both hydrophobic interaction and reversed-phase chromatographic systems using low-molecular weight displacers. The displacers employed for hydrophobic displacement chromatography were water soluble, charged molecules containing several short alkyl and/or aryl groups. Spectroscopy was employed to verify the absence of structural changes to the proteins displaced on these hydrophobic supports. Displacement chromatography on a reversed-phase material was employed to purify a growth factor protein from its closely related variants, demonstrating the high resolutions that can be achieved by hydrophobic displacement chromatography. This process combines the high-resolution/high-throughput characteristics of displacement chromatography with the unique selectivity of these hydrophobic supports and offers the chromatographic engineer a powerful tool for the preparative purification of proteins.