Synthetic oligopeptides as isoelectric point markers for capillary isoelectric focusing with ultraviolet absorption detection

Strategies for capillary electrophoresis: Method development and validation for pharmaceutical and biological applications-Updated and completely revised edition

This review is in support of the development of selective, precise, fast, and validated capillary electrophoresis (CE) methods. It follows up a similar article from 1998, Wätzig H, Degenhardt M, Kunkel A. "Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications," pointing out which fundamentals are still valid and at the same time showing the enormous achievements in the last 25 years. The structures of both reviews are widely similar, in order to facilitate their simultaneous use. Focusing on pharmaceutical and biological applications, the successful use of CE is now demonstrated by more than 600 carefully selected references. Many of those are recent reviews; therefore, a significant overview about the field is provided. There are extra sections about sample pretreatment related to CE and microchip CE, and a completely revised section about method development for protein analytes and biomolecules in general. The general strategies for method development are summed up with regard to selectivity, efficiency, precision, analysis time, limit of detection, sample pretreatment requirements, and validation.

Optimization of an IgG1 CIEF separation by using narrow-range ampholytes and DMSO as protein solubilizer

CIEF is a powerful separation tool utilized in the characterization and relative quantitation of therapeutic mAb charged isoforms. However, one CIEF method is not capable of separating all mAbs with high resolution and reproducibility. Optimization of sample composition and separation parameters is expected when developing a CIEF method for a specific mAb. This paper summarizes a root cause investigation into why a validated CIEF separation method for MAK33 (a type of IgG1) was no longer reproducible. In addition, this paper introduces the concept of sample focusing volume, which is defined as the actual capillary volume occupied by the sample after focusing and explains why there is less protein precipitation and aggregation when using narrow-range ampholytes than broad-range ampholytes. The use of DMSO as protein solubilizer and possible replacement of urea is also explored in this work. Finally, this paper demonstrates that a new optimized CIEF method can achieve over 100 reproducible high-resolution separations of MAK33 per neutral-coated capillary.

Purification and partial characterization of a novel fibrinogenase from the venom of Deinagkistrodon acutus: inhibition of platelet aggregation

A novel fibrinogenase, DAnase, was purified from the venom of Deinagkistrodon acutus by a combination of anion and cation exchange chromatography. Unlike other fibrinogenases which are usually single polypeptide chain proteins, the enzyme was a disulfide-linked dimer with an isoelectric point of 6.03 and an apparent molecular weight of 25kDa on SDS-polyacrylamide gel electrophoresis. DAnase showed α-fibrinogenase activity devoid of fibrinolytic activity. It hydrolyzed rapidly the Aα-chain of fibrinogen and followed by the Bβ-chain and did not cleave the γ-chain. It also exhibited arginine esterase activity. The fibrinogenolytic and arginine esterase activities were completely inhibited by phenylmethanesulfonyl fluoride or tris-(2-carboxyethyl)phosphine hydrochloride, but not by EDTA, indicating that DAnase is a serine protease requiring disulfide bridge(s) for its activity. The protease strongly inhibited ADP-induced platelet aggregation in human platelet-rich plasma but was lack of ADPase activity, indicating that its fibrinogenolytic activity is involved in its inhibition of ADP-induced platelet aggregation. DAnase was devoid of hemorrhagic activity and Factor XIII activation activity. DAnase may have a potential clinical application for the therapy of thrombosis disease.

Charge heterogeneity of a therapeutic monoclonal antibody conjugated with a cytotoxic antitumor antibiotic, calicheamicin

A robust and highly reproducible capillary isoelectric focusing (cIEF) method for the evaluation of charge heterogeneity of monoclonal antibody (mAb) pharmaceutical which contains covalently bound antitumor compounds was developed using a combination of commercially available dimethylpolysiloxane-coated capillary and carrier ampholyte. In order to optimize major analytical parameters for robust mobilization, experimental responses from three pI markers were selected. The optimized method gave excellent repeatability and intermediate precision in estimated pI values of charge variants with relative standard deviations (RSDs) of not more than 0.06% and 0.95%, respectively, when using IgG(4) as a model. Furthermore, RSDs of charge variant compositions were less than 5.0%. These results suggest that the proposed method can be a powerful tool for reproducible evaluation of charge variants of both naked mAbs and their conjugates with high resolution, and it is applicable to quality testing and detailed characterization in the pharmaceutical industry. In addition, it should be noticed that the method provided non-linear pH gradient within the tested ranges, from pI 9.50 to 3.78, and the pH gradient caused the inconsistency of estimated pI ranges between cIEF and gel IEF. This result indicates that selecting appropriate pI markers based on the target pI ranges of charge variants for each mAb related pharmaceutical is highly recommended for the precise determination of pI values.

Novel staining-free proteomic method for simultaneous identification of proteins and determination of their pI values by using low-molecular-mass pI markers

A new proteomic staining-free method for simultaneous identification of proteins and determination of their pI values by using low-molecular-mass pI markers is described. It is based on separation of proteins in gels by IEF in combination with mass spectrometric analysis of both peptides derived by in-gel digestion and low-molecular-mass pI markers extracted form the same piece excised from the gel. In this method, the pI markers are mixed with a protein mixture (a commercial malted barley protein extract) deposited on a gel and separated in a pH gradient. Color pI markers enable supervision of progress of focusing process. Several separated bands of the pI markers (including separated proteins) were excised and the pI markers were eluted from each gel piece by water/ethanol and identified by MALDI-TOF/TOF MS. The remaining carrier ampholytes were then washed out from gel pieces and proteins were in-gel digested with trypsin or chymotrypsin. Obtained peptides were measured by MALDI-TOF/TOF MS and proteins were identified via protein database search. This procedure allows omitting time-consuming protein staining and destaining procedures, which shortens the analysis time. For comparison, other IEF gels were stained with CBB R 250 and proteins in the gel bands were identified. Similarity of the results confirmed that our approach can give information about the correct pI values of particular proteins in complex samples at significantly shorter analysis times. This method can be very useful for identification of proteins and their post-translational modifications in prefractioned samples, where post-translational modifications (e.g., glycation) are frequent.

Profiling recombinant major birch pollen allergen Bet v 1a and carbamylated variants with CZE and CIEF

A preparation of recombinant birch pollen allergen of Betula verrucosa isoform 1a (Bet v 1a) containing chemically modified (carbamylated) variants has been analyzed by CZE and CIEF. In CZE, employing a 100 mmol/L MES buffer at pH 6.50, with 0.4 mmol/L tetraethylenepentamine (TEPA) added, allowed for the resolution of 17 protein fractions. The CIEF profiling of the allergen preparation required a combination of a wide-pH-range carrier ampholyte (CA) of pH 3-10 with two narrow-range CAs of pH 5-6 and 5-7. For CIEF, 91 mmol/L of glycine at pH 2.12 and 20 mmol/L of CHES at pH 10.00 were applied as anolyte and catholyte, respectively. The generated pH gradient was nonlinear with a flat slope for pH 4-6, thus providing an improved resolution. In CIEF, up to 18 protein fractions were distinguished as well. The pI of the target allergen Bet v 1a was 4.9 as determined by means of two pI marker compounds flanking the allergen. Relative purity of the target allergen within the preparation containing carbamylated variants was in accordance for both separation systems and varied between 40.7 and 42.8%.

Peak identification in capillary isoelectric focusing using the concept of relative peak position as determined by two isoelectric point markers

In CIEF analysis, sample peaks can be identified by their relative peak positions (RPP) that are determined using only two internal pI markers. The two internal pI marker peaks should bracket, as close as possible, the sample peaks. The RPP values of the sample peaks are then calculated using the pI values, peak positions of the two pI markers, and peak position of the sample. Use of this method can effectively compensate for pH gradient distortions that often occur as a result of salts. Also, as shown by the results of this paper, regardless of the linearity of the pH gradient established by the given carrier ampholytes, sample peaks can be identified within an SD of 0.1 pH unit in RPP (<2% RSD) as long as the sample is run using the same carrier ampholytes and maintaining salt concentrations in the range of 0-15 mM.

Two-Dimensional Microcolumn Separation Platform for Proteomics Consisting of On-Line Coupled Capillary Isoelectric Focusing and Capillary Electrochromatography. 1. Evaluation of the Capillary-Based Two-Dimensional Platform with Proteins, Peptides, and Human Serum

In this report, an on-line coupling of capillary isoelectric focusing (CIEF) to capillary electrochromatography (CEC) is developed via a nanoinjector valve for performing two-dimensional (2D) proteomics separation. CIEF constitutes the first separation dimension, while CEC operates as the second separation dimension. Besides the orthogonal migration mechanisms of the two capillary-based separation modes, which lead to a 2D system whose overall peak capacity is the product of the peak capacity of the individual modes, the solvent of the CIEF mode is a weak eluent for the reversed-phase CEC (RP-CEC) mode, thus, allowing the transferring of focused fractions from CIEF to CEC without inducing band broadening, and instead zone sharpening would result. In fact, the transferred focused protein fraction from the CIEF column to the CEC column will stay tightly adsorbed to the inlet top of the CEC column until it will be eluted and separated into its protein components with a hydro-organic mobile phase. The theoretical peak capacity of the CIEF-CEC 2D platform is estimated at n(CIEF) (= 560) x n(CEC) (= 97) = 54 320. This peak capacity is more than needed for proteomics profiling. Also, only a fraction of this peak capacity is needed when looking at heart cuts for performing subproteomics. The 2D platform described here offers the convenience to generate the needed peak capacity to solve a given proteomic separation problem. This is facilitated by the RP-CEC dimension, which ensures rapid isocratic separation of proteins and peptides and rapid solvent change and column equilibration and avoids lengthy gradient elution. The RP-CEC column is based on neutral C17 monolith, which offers high separation efficiency and relatively high column permeability. To the best of our knowledge, the proposed 2D platform combining CIEF and CEC is reported for the first time for proteins and proteomics.

Proliferating brain cells are a target of neurotoxic CSF in systemic autoimmune disease

Brain atrophy, neurologic and psychiatric (NP) manifestations are common complications in the systemic autoimmune disease, lupus erythematosus (SLE). Here we show that the cerebrospinal fluid (CSF) from autoimmune MRL-lpr mice and a deceased NP-SLE patient reduce the viability of brain cells which proliferate in vitro. This detrimental effect was accompanied by periventricular neurodegeneration in the brains of autoimmune mice and profound in vivo neurotoxicity when their CSF was administered to the CNS of a rat. Multiple ionic responses with microfluorometry and protein peaks on electropherograms suggest more than one mechanism of cellular demise. Similar to the CSF from diseased MRL-lpr mice, the CSF from a deceased SLE patient with a history of psychosis, memory impairment, and seizures, reduced viability of the C17.2 neural stem cell line. Proposed mechanisms of cytotoxicity involve binding of intrathecally synthesized IgG autoantibodies to target(s) common to different mammalian species and neuronal populations. More importantly, these results indicate that the viability of proliferative neural cells can be compromised in systemic autoimmune disease. Antibody-mediated lesions of germinal layers may impair the regenerative capacity of the brain in NP-SLE and possibly, brain development and function in some forms of CNS disorders in which autoimmune phenomena have been documented.

Analysis of human blood serum using the off-line coupling of capillary isoelectric focusing to matrix-assisted laser desorption/ionization time of flight mass spectrometry

Off-line coupling of capillary IEF (CIEF) with matrix-assisted laser desorption/ionization mass spectrometry was utilized for the analysis of human blood serum. Serum proteins were initially separated by CIEF, and fractions of the isoelectric separation were eluted sequentially to a MALDI-TOF MS sample target. During pressure elution of the CIEF sample, voltage was maintained across the capillary system utilizing a sheath flow arrangement to minimize band broadening induced by the laminar flow field. Both pI and mass information were obtained from the complex biological sample, similar to traditional 2-DE techniques, and the platform was faster (hours versus days), more automatable, and simpler than 2-DE. The volume of raw sample present in the actual analysis was approximately 100 nL, making this technique well suited for very rare specimens. Additionally, the speed and simplicity of the technology make it an attractive technique for performing initial comparative analyses of complex samples.

Colored pI standards and gel isoelectric focusing in strongly acidic pH

Colored, low molecular weight pI markers have been developed for isoelectric focusing (IEF) in acidic pH range. Their isoelectric points (pIs) were determined by direct measurement of the pH of the focused bands after completion of IEF on polyacrylamide gels. The practicable suitability of the proposed pI markers as pI standards for IEF was tested by applying gel IEF. The acidic pH gradient was created either by commercial synthetic carrier ampholytes or by mixture of simple buffers consisting of acids (non-ampholytes) and ampholytic buffers. By applying simple acids, it was possible to extend the acidic pH range beyond those achievable with commercial synthetic carrier ampholytes. By using an experimental arrangement without electrode electrolyte reservoirs with electrodes creating the fixed end of the gel, the strongly acidic pH gradient was stable even for prolonged focusing time.

On-line capillary isoelectric focusing–mass spectrometry for quantitative analysis of peptides and proteins

On-line capillary isoelectric focusing-mass spectrometry (cIEF-MS) was applied to determine concentrations of peptides and proteins using angiotensin II and human tetrasialo-transferrin as the model samples. The concentration of the carrier ampholyte was optimized for both resolution and ion intensity. cIEF-MS employing 1% Pharmalyte 3-10 and a sheath liquid containing water/methanol/acetic acid (50/49/1) resolved angiotensin I and II (5 microM each, DeltapI=0.2) at an Rs value of 2.29. The determined concentration of angiotensin II (0.1-5 microM) well correlated (R=0.999) with that obtained by the conventional RP-HPLC method. The limit of detection was 0.22 microM, which was about 10 times lower than that by UV detection (2 microM). The repeatability and accuracy were <15 and <11%, respectively. cIEF-MS was also applied to determine human tetrasialo-transferrin concentration. The good linearity (R2=0.998) was also observed between the transferrin concentration (0.5-1.2 g/L) and peak area ratio (IS; beta-lactoglobulin B) with acceptable accuracy (<1.9%) and repeatability ( approximately 10% at 1g/L).

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.

Dynamics of gel isoelectric focusing with ampholytic dyes monitored by camera in real-time

The dynamics of gel isoelectric focusing were studied by using amphoteric low-molecular-mass colored substances (isoelectric point markers). The polyacrylamide gel in slab format was in direct contact with the electrodes. In addition to isoelectric focusing with a pH gradient composed of synthetic carrier ampholytes, pH gradients created by simple buffers of acetic acid, 2-(N-morpholino)ethanesulfonic acid, histidine and N,N,N',N'-tetramethylethylenediamine were applied. The progress of the electrofocusing process was monitored by a charge-coupled device camera and video recording. The gradient profile and dynamics were approximated from the positions of isoelectric point markers, which were focused both on boundaries between individual zones of simple buffers and within the zones themselves. The obtained animated records enabled the observation of the entire real focusing run within fractions of a minute, which is useful both for the understanding and optimization of the focusing.

Differential maintenance and de novo methylating activity by three DNA methyltransferases in aging and immortalized fibroblasts

Genomic methylation, which influences many cellular processes such as gene expression and chromatin organization, generally declines with cellular senescence although some genes undergo paradoxical hypermethylation during cellular aging and immortalization. To explore potential mechanisms for this process, we analyzed the methylating activity of three DNA methyltransferases (Dnmts) in aging and immortalized WI-38 fibroblasts. Overall maintenance methylating activity by the Dnmts greatly decreased during cellular senescence. In immortalized WI-38 cells, maintenance methylating activity was similar to that of normal young cells. Combined de novo methylation activity of the Dnmts initially decreased but later increased as WI-38 cells aged and was strikingly elevated in immortalized cells. To further elucidate the mechanisms for changes in DNA methylation in aging and immortalized cells, the individual Dnmts were separated and individually assessed for maintenance and de novo methylating activity. We resolved three Dnmt fractions, one of which was the major maintenance methyltransferase, Dnmt1, which declined steadily in activity with cellular senescence and immortalization. However, a more basic Dnmt, which has significant de novo methylating activity, increased markedly in activity in aging and immortalized cells. We have identified this methyltransferase as Dnmt3b which has an important role in neoplastic transformation but its role in cellular senescence and immortalization has not previously been reported. An acidic Dnmt we isolated also had increased de novo methylating activity in senescent and immortalized WI-38 cells. These studies indicate that reduced genome-wide methylation in aging cells may be attributed to attenuated Dnmt1 activity but that regional or gene-localized hypermethylation in aging and immortalized cells may be linked to increased de novo methylation by Dnmts other than the maintenance methyltransferase.

Fluorescence-labeled peptide pI markers for capillary isoelectric focusing

Nineteen fluorescent pH standards or pI markers ranging pH 3.64-10.12 were developed for use in capillary isoelectric focusing using laser-induced fluorescence detection. Tetra- to tridecapeptides containing one cysteine residue were designed to focus sharply at their respective isoelectric points by including amino acids that contain charged side chains, the pKa values of which are close to the corresponding pI values. An iodoacetylated derivative of tetramethylrhodamine was coupled to the thiol group of cysteine to yield fluorescent pI markers. The pI values of the labeled peptides were precisely determined after isoelectric focusing on polyacrylamide gel slabs by direct measurement of the pH of the focused bands. The markers were subjected to capillary isoelectric focusing for 10-15 min in coated capillaries under conditions of low electroosmosis and were detected by means of a scanning laser-induced fluorescence detector down to a level of subpicomolar range. The markers permitted the calibration of a wide-range pH gradient formed in a capillary by fluorescence detection for the first time and should facilitate the development of highly sensitive analytical methods based on a combination of capillary isoelectric focusing and laser-induced fluorescence detection.

Recent advances in capillary electrophoresis of peptides

The article gives a comprehensive review on the recent developments in the applications of high-performance capillary electromigration methods, including zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography and electrochromatography, to analysis, preparation and physicochemical characterization of peptides. The article presents new approaches to the theoretical description and experimental verification of electromigration behavior of peptides, and covers the methodological aspects of capillary electroseparations of peptides, such as strategy and rules for the rational selection of separation mode and experimental conditions, sample treatment, suppression of peptide adsorption to the inner capillary wall, new developments in individual separation modes and new designs of detection systems. Several types of applications of capillary electromigration methods to peptide analysis are presented: conventional qualitative and quantitative analysis for determination of purity, determination in biomatrices, monitoring of physical and chemical changes and enzymatic conversions, amino acid and sequence analysis and peptide mapping of proteins. Some examples of micropreparative peptide separations are given and capabilities of capillary electromigration techniques to provide important physicochemical characteristics of peptides are demonstrated.

Capillary electrophoresis of proteins 1999-2001

This review article with 223 references describes recent developments in capillary electrophoresis (CE) of proteins and covers papers published during last two years, from the previous review (V. Dolnik, Electrophoresis 1999, 20, 3106-3115) through Spring 2001. It describes the topics related to CE of proteins including modeling of the electrophoretic properties of proteins, sample pretreatment, wall coatings, improving selectivity, detection, special electrophoretic techniques, and applications.

Capillary isoelectric focusing with UV-induced fluorescence detection

Low-molecular-mass fluorescent compounds excitable in the near UV region with suitable acidobasic and electrophoretic properties are suggested as isoelectric point (pI) markers for isoelectric focusing (IEF) with UV photometric and UV excited fluorometric detection. The experimental set-up of capillary IEF with UV excited fluorometric detection and properties of new UV-induced fluorescent pI markers are given. The pI values of 18 new pI markers determined independently of IEF methods range from 2.1 to 10.3. The examples of separation of new pI markers together with derivatized proteins by capillary IEF with photometric or fluorometric detection are presented.

Accuracy in the determination of isoelectric points of some proteins and a peptide by capillary isoelectric focusing: utility of synthetic peptides as isoelectric point markers

To evaluate the accuracy ofisoelectric point determination by capillary isoelectric focusing, the pI values of nine proteins and a peptide, the pI values of which had been determined by other methods and ranging pI 3.55-9.60, were determined by capillary isoelectric focusing by cofocusing of recently developed peptide pI markers ranging 3.38-10.17, and the consistency of the pI values was examined. Isoelectric focusing was carried out in neutral polymer-coated capillaries, and the pH gradient was mobilized by pressure toward the cathode, to detect samples with absorption at 280 nm at a fixed detection point. Carrier ampholytes from two different suppliers and in different pH ranges were used. The sharp peaks of the highly pure peptide pI markers greatly facilitated the unambiguous identification of the peaks. When a carrier ampholyte ranging over the acidic side was used, the detection of acidic pI samples was anomalously delayed. This could be partly mitigated by reducing the viscosity of the anode solution in comparison with the pH gradient formed in the capillary. Since the detection times vs the pH relationships were not linear in most cases, the use of a linear calibration line over an entire pH gradient would be erroneous. Instead, the pI values of samples were calculated by assuming a linear relation for pH against detection time between two flanking marker peptides. Close agreement between the pI values, determined by capillary isoelectric focusing, and the reference values of the samples was observed within an average difference range of 0.04-0.08 pH unit with a sample consumption of 10-100 ng within 30-60 min. Some carrier ampholytes were preferentially more effective at either the acidic or the basic side of the pH gradient. For confirmation of the completion of focusing, the use of two different focusing times is recommended.