Electrophoretic methods for process monitoring and the quality assessment of recombinant glycoproteins

Analysis of protein phosphorylation combining capillary electrophoresis with ATP analog labeling technique

Protein phosphorylation is one of the most basic mechanisms for regulating and controlling protein biological activity and function, and it is also a very important posttranslational modification process. Protein phosphorylation participates in and regulates many life activities such as signal transduction, gene expression, cell cycle, and so on. In this paper, we propose a method for the determination of the protein phosphorylation combining capillary electrophoresis (CE) with ATP analog labeling technique. We synthesized two new ATP analogs (ATP-NB and ATP-TATD-NB) functionalized by norbornene. Using Abl kinase as a model, we established a method for the determination of the kinase activity in solution and lysate by CE with laser-induced fluorescence detection (CE-LIF). This method was used to evaluate the efficiencies of kinase inhibitors. The IC₅₀ values obtained are basically consistent with the reports. By D-A reaction (inverse electron demand Diels-Alder reaction) to label TZ-BODIPY fluorescence, we also realized the phosphorylation fluorescence detection of substrate peptide. Then, we used fluorescence confocal microscopy imaging technology to study the phosphorylation of proteins in vivo by the D-A reaction of ATP-NB and TZ-BODIPY. Our preliminary results documented that the combination of CE-LIF with analog ATP-NB labeling technique is an effective strategy for the determination of the protein phosphorylation and the kinase activity and for screening of kinase inhibitors. The D-A reaction of ATP-NB and TZ-BODIPY also laid the foundation for the subsequent in situ study of protein phosphorylation.

Highly sensitive method for specific, brief, and economical detection of glycoproteins in sodium dodecyl sulfate-polyacrylamide gel electrophoresis by the synthesis of a new hydrazide derivative

A new hydrazide derivative was synthesized and used for the first time as a specific, brief, and economical probe to selectively visualize glycoproteins in 1-D and 2-D sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with high sensitivity. The detection limit of the newly developed staining method is 2- and 4-fold higher than that of the widely used Pro-Q Emerald 300 and 488 stains, respectively.

A new fluorescent quenching method for the determination of phosphoproteins by using calconcarboxylic acid

A fluorescent quenching detection method for phosphoproteins in SDS-PAGE by using calconcarboxylic acid (CCA) was described. In this method, the fluorescence intensity of CCA was greatly increased with the presence of Al(3+) in the gel background, while in zones where phosphoproteins are located this intensity was absent because of fluorescence quenching phenomenon through the formation of CCA-Al(3+) -phosphoprotein appended complex. Approximately 4-8 ng of phosphoproteins can be selectively detected within 1 h (1D SDS-PAGE), which is similar to that of the most commonly used Pro-Q Diamond stain. The specificity of this novel technique for phosphoproteins was confirmed by dephosphorylation, Western blot, and LC-MS/MS analysis, respectively. Furthermore, to better understand the newly developed method, the detection mechanism of CCA stain was explored by fluorescent spectrometry. According to the results, it is believed that CCA stain may provide a new choice for selective, economical, MS compatible, and convenient visualization of gel-separated phosphoproteins.

Fluorescent staining of glycoproteins in sodium dodecyl sulfate polyacrylamide gels by 4H-[1]-benzopyrano[4,3-b]thiophene-2-carboxylic acid hydrazide

A sensitive, specific, economic and MS compatible staining method for gel-separated glycoproteins by using BH was described and demonstrated by 1-D and 2-D SDS-PAGE, deglycosylation, glycoprotein affinity enrichment and LC-MS/MS, respectively.

Glycosylation: impact, control and improvement during therapeutic protein production

The emergence of the biopharmaceutical industry represented a major revolution for modern medicine, through the development of recombinant therapeutic proteins that brought new hope for many patients with previously untreatable diseases. There is a ever-growing demand for these therapeutics that forces a constant technological evolution to increase product yields while simultaneously reducing costs. However, the process changes made for this purpose may also affect the quality of the product, a factor that was initially overlooked but which is now a major focus of concern. Of the many properties determining product quality, glycosylation is regarded as one of the most important, influencing, for example, the biological activity, serum half-life and immunogenicity of the protein. Consequently, monitoring and control of glycosylation is now critical in biopharmaceutical manufacturing and a requirement of regulatory agencies. A rapid evolution is being observed in this context, concerning the influence of glycosylation in the efficacy of different therapeutic proteins, the impact on glycosylation of a diversity of parameters/processes involved in therapeutic protein production, the analytical methodologies employed for glycosylation monitoring and control, as well as strategies that are being explored to use this property to improve therapeutic protein efficacy (glycoengineering). This work reviews the main findings on these subjects, providing an up-to-date source of information to support further studies.

Simple and specific dual-wavelength excitable dye staining for glycoprotein detection in polyacrylamide gels and its application in glycoproteomics

In this study, a commercially available fluorescent dye, Lissamine rhodamine B sulfonyl hydrazine (LRSH), was designed to specifically stain the glycoproteins in polyacrylamide gels. Through the periodate/Schiff base mechanism, the fluorescent dye readily attaches to glycoproteins and the fluorescence can be simultaneously observed under either 305 nm or 532 nm excitation therefore, the dye-stained glycoproteins can be detected under a regular UV transilluminator or a more elegant laser-based gel scanner. The specificity and detection limit were examined using a standard protein mixture in polyacrylamide gels in this study. The application of this glycoprotein stain dye was further demonstrated using pregnancy urine samples. The fluorescent spots were further digested in gel and their identities confirmed through LC-MS/MS analysis and database searching. In addition, the N-glycosylation sites of LRSH-labeled uromodulin were readily mapped via in-gel PNGaseF deglycosylation and LC-MS/MS analysis, which indicated that this fluorescent dye labeling does not interfere with enzymatic deglycosylation. Hence, the application of this simple and specific dual-wavelength excitable dye staining in current glycoproteome research is promising.

Fluorescence detection of glycoproteins in gels and on electroblots

Glycosylation of proteins is a dynamic post-translational modification commonly found in eukaryotes, changing with development, differentiation, and disease state. Identification of glycoproteins is important for completely characterizing the population of proteins found at a given point in time. This unit contains protocols for identifying glycoproteins in general using a fluorescence based periodate/Schiff base method and those containing specific carbohydrates using a lectin-based fluorescent method.

Analysis of plasma protein adsorption onto PEGylated nanoparticles by complementary methods: 2-DE, CE and Protein Lab-on-chip system

The biodistribution of colloidal carriers after their administration in vivo depends on the adsorption of some plasma proteins and apolipoproteins on their surface. Poly(methoxypolyethyleneglycol cyanoacrylate-co-hexadecylcyanoacrylate) (PEG-PHDCA) nanoparticles have demonstrated their capacity to cross the blood-brain barrier (BBB) by a mechanism of endocytosis. In order to clarify this mechanism at the molecular level, proteins and especially apolipoproteins adsorbed at the surface of PEG-PHDCA nanoparticles were analyzed by complementary methods such as CE and Protein Lab-on-chip in comparison with 2-D PAGE as a method of reference. Thus, the ability of those methodologies to identify and quantify human and rat plasma protein adsorption onto PEG-PHDCA nanoparticles and conventional PHDCA nanoparticles was evaluated. The lower adsorption of proteins onto PEG-PHDCA nanoparticles comparatively to PHDCA nanoparticles was evidenced by 2-D PAGE and Protein Lab-on-chip methods. CE allowed the quantification of adsorbed proteins without the requirement of a desorption procedure but failed, in this context, to analyze complex mixtures of proteins. The Protein Lab-on-chip method appeared to be very useful to follow the kinetic of protein adsorption from serum onto nanoparticles; it was complementary to 2-D PAGE which allowed the identification (with a relative quantification) of the adsorbed proteins. The overall results suggest the implication of the apolipoprotein E in the mechanism of passage of PEG-PHDCA nanoparticles through the BBB.

Profiling preparations of recombinant birch pollen allergen Bet v 1a with capillary zone electrophoresis in pentamine modified fused-silica capillaries

Three preparation batches of the recombinant birch pollen allergen Bet v 1a have been analyzed by capillary zone electrophoresis (CZE) using a separation electrolyte consisting of 100 mmol L(-1) phosphate at pH 6.50 with 2.0 mmol L(-1) tetraethylenepentamine (TEPA) added. TEPA improved the resolution by wall shielding and selective attachment to allergens, but reduced migration repeatability at concentrations >2.0 mmol L(-1). Heterogeneity of preparations determined by CZE and electrospray ionization-quadrupole-time-of flight-MS were in accordance and revealed chemically modified (carbamylated) allergens in one of the preparations. The method was validated according to the ICH-guidelines. Repeatability of effective electrophoretic mobility (mu(eff)) was <0.55% R.S.D. (n = 5). Migration time corrected peak areas were used for quantification. Limit of quantification (LOQ) was 25 microg mL(-1) for the major isoform Bet v 1a, based on a signal-to-noise ratio of 10, and detector response was linear between LOQ and 0.90 mg mL(-1). Purity of the different rBet v 1a preparations was determined to be between 40 and 92% depending on the manufacturing protocol.

Glycoprotein Characterization Combining Intact Protein and Glycan Analysis by Capillary Electrophoresis-Electrospray Ionization-Mass Spectrometry

Glycosylated proteins play important roles in a large number of biological processes. Therefore, a complete characterization in terms of glycan structures and glycoform heterogeneity is needed. In this paper, a combined approach based on glycan and intact glycoprotein analysis by capillary zone electrophoresis-electrospray-mass spectrometry (CZE-ESI-MS) is presented. Based on a new capillary coating, a CZE-ESI-MS method for the separation and characterization of intact glycoproteins has been developed and compared to a method recently introduced for the characterization of erythropoietin. The excellent glycoform separation results in high-quality mass spectra, high dynamic range, and good sensitivity, allowing the correct characterization of minor glycan modifications. Additionally, a CZE-ESI-MS separation method for underivatized N-glycans has been developed. The separation of glycans differing in the degree of sialic acids and repeats of noncharged carbohydrates is achieved. The separation power of the method is demonstrated by obtaining mobility differences in glycans differing only by 16 Da. A time-of-flight mass spectrometer allowed the correct identification of the glycan composition based on high mass accuracy and resolution, identifying even minor modifications such as the exchange of "O" by "NH". An ion trap mass spectrometer provided structural information of the underivatized glycans from fragmentation spectra. The general applicability of both methods to glycoprotein analysis is illustrated for erythropoietin, fetuin, and alpha1-acid glycoprotein. The results obtained by the glycan analysis allowed an unequivocal glyco-assignment to the masses obtained for the intact proteins as long as the protein backbone is well characterized. Furthermore, modifications found for intact proteins can be attributed to differences in the glycostructure.

Rapid quantitative capillary zone electrophoresis method for monitoring the micro-heterogeneity of an intact recombinant glycoprotein

A simple high-resolution capillary zone electrophoresis (CZE) method capable of rapidly assessing the micro-heterogeneity of a 24 kDa molecular weight glycoprotein, has been developed. Separation is carried out using a bare silica capillary at a pH of 2.5 in a commercially available electrophoresis buffer system composed of triethanolamine and phosphoric acid. Over 30 peaks were detected within a run time of 15 min using a 27 cm capillary and approximately 60 peaks were detected using a 77 cm capillary. Although most of the peaks arise from differences in the oligosaccharide structures present on the one glycosylation site on this molecule, other forms of micro-heterogeneity due to the presence of the nonglycosylated form of this glycoprotein and various types of chemical degradation, e.g., deamidation, are also responsible for the multitude of peaks observed. Although the exact chemical identity of each peak in the resulting electropherogram of this glycoprotein is not known, useful information can be obtained for assessing comparability, stability, and batch consistency. Factors impacting the resolution, precision, accuracy, and robustness of the assay are also discussed along with inherent advantages and limitations associated with measuring the micro-heterogeneity of intact glycoproteins.

Determination of the isoelectric point of proteins by capillary isoelectric focusing

Different ways of determining isoelectric points (pI) of proteins in capillary isoelectric focusing are reviewed here. Due to the impossibility of direct pH measurements in the liquid phase, such assessments have to rely on the use of pI markers. Different types of pI markers have been described: dyes, fluorescently labelled peptides, sets of proteins of known pI values. It appears that, perhaps, the best system is a set of 16 synthetic peptides, trimers to hexamers, made to contain each a Trp residue for easy detection at 280 nm. By a careful blend of acidic (Asp, Glu), mildly basic, with pK around neutrality (His), and basic (Lys, Arg) amino acids, it is possible to obtain a series of pI markers with pI values quite evenly distributed along the pH scale, possessing good buffering capacity and conductivity around their pI values and thus focusing as sharp peaks. Another approach to pI determination is the monitoring of the current during mobilization: this allows, with the aid of known pI markers, to calibrate the system with a pI/current graph. Pitfalls and common errors in pI determinations are reviewed here and guidelines given for minimizing such errors in pI estimation.

Separation of Recombinant Human Erythropoietin Glycoforms by Capillary Electrophoresis Using Volatile Electrolytes. Assessment of Mass Spectrometry for the Characterization of Erythropoietin Glycoforms

The separation of the glycoforms of erythropoietin (EPO) by capillary electrophoresis (CE) was recently published as a monograph by the European Pharmacopoeia (European Pharmacopoeia 4 2002, 1316, 1123-1128). Although the experimental CE conditions employed a background electrolyte containing additives suitable for on-line UV-absorption detection, they were not appropriate for on-line mass spectrometry (MS) detection. In this work, an attempt was made to investigate experimental conditions employing volatile electrolyte systems to achieve the separation and characterization of EPO glycoforms using CE and ESI-MS methodologies. The influence of several operating conditions, such as the coating of the internal walls of the capillary as well as the composition, concentration, and the pH of the separation buffer were investigated. The results demonstrated that when the internal walls of the capillaries were permanently coated with Polybrene and a buffer electrolyte containing 400 mM of HAc-NH4Ac (acetic acid-ammonium acetate), pH 4.75, was used, a significantly reproducible separation was achieved for EPO glycoforms. Intact EPO was characterized by two mass spectrometry techniques: electrospray ionization (ESI-MS) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF-MS). The data demonstrated that MALDI-TOF-MS provided a good approximation to an average molecular mass of the EPO molecule. However, it was still necessary to carry out further separation of the intact EPO glycoforms in order to obtain molecular mass information when ESI-MS was used.

Review applications of capillary electrophoresis to the analysis of biotechnology-derived therapeutic proteins

The number of proteins produced by recombinant DNA technology continues to grow at a rapid pace. In this review, the emphasis is on proteins that are of therapeutic interest. Aspects of protein analysis, such as glycoform separation of proteins produced in mammalian cells and the separation of oligosaccharides for structure elucidation, are covered. The use of antibodies as therapeutic proteins is growing and currently antibodies are the largest class of proteins produced by biotechnology. This has merited a separate section on analysis of antibodies by capillary electrophoresis (CE). Applications of mass spectrometry as an ancillary technique, used in conjunction with CE, are also covered briefly. This review covers the literature since 1999.

Routine o-glycan characterization in nutritional supplements--a comparison of analytical methods for the monitoring of the bovine kappa-casein macropeptide glycosylation

Analytical procedures, including capillary isoelectric focusing (CIEF), high-performance anion-exchange chromatography coupled to amperometric detection (HPAEC-PAD) and normal-phase chromatography with fluorescence detection are presented for the characterization of a highly O-glycosylated caseinomacropeptide (CGMP) and the detection of subtle glycosylation differences between CGMP Batches obtained with two different preparation procedures. Modified two-step CIEF allowed monitoring of glycopeptide heterogeneity and determination of the isoelectric points of acidic glycoforms. The mixture of wide and narrow pH range ampholytes was optimized to improve glycoform resolution. The pI of the different CGMP glycoforms was evaluated with pI internal standards and found to range between 3.08 and 3.58, which indicates a very acidic glycopeptide. Moreover, the monosaccharide composition was determined with HPAEC-PAD after neutral and amino sugars release by using adequate acidic hydrolysis of CGMP. Results indicated a similar composition for Batches I and II, but the monosaccharide percentages were 3-4 fold higher in Batch I, particularly for galactose and glucose. This likely reflects a higher content in lactose in the case of Batch I. Finally, O-linked oligosaccharides were released with an automated hydrazinolysis and derivatized with a sensitive labelling reagent, 2-aminobenzamide. The derivatives were then analyzed by normal-phase HPLC coupled with fluorescence detection, and separated on the basis of hydrophilic interaction, which allowed oligosaccharide mapping of the two CGMP. It appeared that the two CGMP preparations had an almost identical O-glycan population, but CGMP Batch I was more glycosylated than Batch II. Additionally, the sizes of the separated glycans, expressed as the number of glucose units, were tentatively assigned using calibration with a partial hydrolysate of dextran. In conclusion, a combination of electrophoretic and chromatographic techniques was found powerful in studying glycoprotein heterogeneity and assessing batch-to-batch consistency.

One-step capillary isoelectric focusing for the separation of the recombinant human immunodeficiency virus envelope glycoprotein glycoforms

One-step capillary isoelectric focusing was investigated as a rapid method to resolve the glycoforms of the heterogeneous recombinant human immunodeficiency virus (HIV) envelope glycoprotein (rgp 160sMN/LAI). The separation was performed in a poly(vinyl alcohol) (PVA) coated capillary using a mixture of ampholyte of narrow and wide pH range. A combination of saccaharose and 3-(cyclohexylamino)-1-propanesulfonic acid was shown to be the most efficient additive to avoid protein precipitation which occurs at a pH close to its pI. Although the calibration curve [isoelectric point (pI) vs. migration times] showed a non-linear relationship, an adequate linearity could be yielded for short pI ranges permitting to exhibit the acidic character of the different glycoforms of the rgp 160s MN/LAI (pI from 4.00 to 4.95). Reproducibility evaluated by comparing the performance of a polyacrylamide and a PVA coated capillary showed that low RSD values were obtained for intra-day (0.5 to 1.9%) and inter-day (1.6 to 7.6%) measurements using the PVA capillary. Moreover, the long term stability of the PVA capillary was demonstrated by measuring the variation of migration times of the protein markers for a long period of use. Finally, this method was able to differentiate the glycoform pattern of two close glycoproteins such as the rgp 160 of two sub-populations of the virus HIV-1.

Applications of capillary electrophoresis in biotechnology

Capillary electrophoresis (CE)-related techniques are increasingly being used as a matter of routine practice in the biotechnology discipline. Since recombinant DNA-derived proteins and the antisense oligonucleotides constitute a large portion of the applications of these techniques, they have been emphasized in this review. Analyses by CE of Escherichia coli-derived proteins and glycosylated proteins derived from mammalian cell cultures are summarized, as well as those of the carbohydrate chains that have been enzymatically removed from the protein. Applications of CE in the analysis of the antisense oligonucleotides for the determination of purity and the analytical studies on the metabolism of these modified oligonucleotides, by CE are reviewed. The literature mainly covers the period from 1996.

Recent developments in capillary electrophoresis and capillary electrochromatography of carbohydrate species

This review article is concerned with the recent developments in capillary electrophoresis (CE) and capillary electrochromatography (CEC) of carbohydrates. The literature shows that CE possesses impressive potential in the analysis of carbohydrates. On the other hand, CEC has just started to show promise in the analysis of carbohydrates. Advances in separation and detection approaches of derivatized and underivatized carbohydrates are discussed based on the available literature. In addition, important applications are illustrated.

Recent developments in capillary zone electrophoresis of proteins

This review article with 125 references describes recent developments in capillary zone electrophoresis of proteins. It encompasses approximately the last two years, from the previous review (V. Dolník, Electrophoresis 1997, 18, 2353-2361) through Spring 1999. Topics covered include modeling of the electrophoretic properties of proteins, sample preconcentration and derivatization, wall coatings, improving selectivity, special detection techniques, and applications.

Capillary electrophoresis of proteins for proteomic studies

Analyses of proteins in complex mixtures such as cell lyzates are presently performed mainly by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. For structural analysis, each protein in a spot is digested with proteases and the fragment peptides are subjected to Edman sequencing and/or mass spectrometry. These works aim at the total analysis of proteins in a complex mixture and reconstruction of their cooperative functions. Genomic studies are now being combined with these proteomic studies. This review article focuses on the application of capillary electrophoresis aiming at the total analysis of complex protein systems or structural analysis of each separated protein. From this viewpoint, articles on capillary zone electrophoresis, capillary isoelectric focusing, and sieving SDS capillary electrophoresis are reviewed. Since these techniques of capillary electrophoresis have been thoroughly reviewed previously, papers published in 1997 and 1998 are mainly covered.