Collection of alpha1-acid glycoprotein molecular species by capillary electrophoresis and the analysis of their molecular masses and carbohydrate chains. Basic studies on the analysis of glycoprotein glycoforms

Glycoprotein analysis using lectin microcolumns and capillary electrophoresis: Characterization of alpha1-acid glycoprotein by combined separation methods

Separations based on combinations of 2.1 mm I.D. high-performance affinity microcolumns and capillary electrophoresis were developed and used to characterize the glycoforms of an intact glycoprotein. Human alpha₁-acid glycoprotein (AGP) was used as a model analyte due to its heterogeneous glycosylation resulting from variations in its degree of branching, fucosylation, and number of sialic acids. Three separation formats were examined based on microcolumns that contained the lectins concanavalin A (Con A) or Aleuria aurantia lectin (AAL). These microcolumns were used with one another or in combination with capillary electrophoresis. N-Glycan analysis of the non-retained and retained AGP fractions was carried out by using PNGase F digestion and nanoflow electrospray ionization mass spectrometry. Con A microcolumns were found to selectively enrich AGP that contained bi-antennary N-glycans, while AAL microcolumns retained AGP with fucose-containing N-glycans. Results from these separation methods indicated that fucosylation of the N-linked glycans was more abundant when a high degree of branching was present in AGP. Sialic acid residues were more abundant when higher degrees of branching and more fucose residues were present in AGP. The separation and analysis methods that were developed could be used with relatively small amounts of AGP and can be adapted for use with other intact glycoproteins.

Glycan analysis for protein therapeutics

Glycosylation can be a critical quality attribute for protein therapeutics due to its extensive impact on product safety and efficacy. Glycan characterization is important in the process of protein drug development, from early stage candidate selection to late stage regulatory submission. It is also an indispensable part in the evaluation of biosimilarity. This review discusses the effects of glycosylation on the stability and activity of protein therapeutics, regulatory considerations corresponding to manufacturing and structural characterization of glycosylated protein therapeutics, and focuses on mass spectrometry compatible separation methods for glycan characterization of protein therapeutics. These approaches include hydrophilic interaction liquid chromatography, reversed-phase liquid chromatography, capillary electrophoresis, porous graphitic carbon liquid chromatography and two-dimensional liquid chromatography. Advances and novelties in each separation method, as well as associated challenges and limitations, are discussed at the released glycan, glycopeptide, glycoprotein subunit and intact glycoprotein levels.

Glycoform analysis of alpha1-acid glycoprotein based on capillary electrophoresis and electrophoretic injection

A method based on capillary electrophoresis (CE) with electrophoretic injection and absorbance detection was developed for the direct analysis of AGP glycoforms in human serum. Electrophoretic injection of AGP was performed in the reversed-polarity mode of CE with a capillary coated with poly(ethylene oxide) and that had minimal electroosmotic flow. This situation created an essentially stationary interface between the sample and running buffer during injection and sample stacking. This approach allowed an 11,000-fold increase in sample loading for a 5min injection versus hydrodynamic injection and without introducing any significant levels of extra band-broadening. This method was used with sample pretreatment methods based on acid precipitation and desalting to examine AGP glycoforms in only 65μL of serum. A limit of detection of 2.1-11.3nM was obtained for the major AGP glycoform bands in serum, and the sample pretreatment method gave a recovery of 72.3-80.9% for these glycoforms. The precision for the migration times was ±0.08-0.13% and the precision for the peak areas was ±0.34-1.18% when using serum samples and an internal standard. This method was used for both normal pooled serum and serum from individuals with systemic lupus erythematosus. Results were obtained in a separation time of 25min and allowed the comparison of up to eleven glycoform bands in these samples. A similar approach may be useful in examining additional glycoproteins in serum or other types of biological samples.

Glycoform analysis of alpha1-acid glycoprotein by capillary electrophoresis

A relatively fast and reproducible CE separation was developed for the glycoform analysis of α1-acid glycoprotein (AGP). Factors that were considered included the pH for this separation and various techniques for coating the capillary and/or to minimize electroosmotic flow and protein adsorption. Optimum resolution of the AGP glycoforms was obtained at pH 4.2 with a running buffer containing 0.1% Brij 35 and by using static and dynamic coatings of PEO on the capillary. These conditions made it possible to separate nine AGP glycoform bands in about 20min. The limit of detection (based on absorbance measurements) ranged from 0.09 to 0.38μM for these AGP glycoform bands, and the linear range extended up to a total AGP concentration of at least 240μM. The migration times for the glycoform bands had typical within-day and day-to-day precisions of ±0.16-0.23% or less, respectively, on a single treated capillary and the variation between capillaries was ±0.56% or less. A charge ladder approach was employed to examine the mass or charge differences in the glycoforms that made up these bands, giving a good fit to a model in which the neighboring bands differed by one charge (e.g., from a sialic acid residue) and had an average mass difference of approximately 0.7-0.9kDa. The approaches used to develop this separation method are not limited to AGP but could be extended to the analysis of other glycoproteins by CE.

Structural glycobiology of human α1-acid glycoprotein and its implications for pharmacokinetics and inflammation

Human α1-acid glycoprotein (AGP) is an abundant human plasma glycoprotein that may be N-glycosylated at five positions. AGP plays important roles on pharmacokinetics and can rise up to 5-fold in inflammatory events. In such events, the glycan chains attached to Asn54, Asn75 and Asn85 may become fucosylated, originating a sialyl-Lewis X epitope. This epitope, in turn, can bind selectin proteins. Such interplay is important for immunomodulation. While the X-ray structure of unglycosylated AGP has been reported, the absence of the glycan chains hampered the further insights into its structural biology and, ultimately, into its biological function. Thus, the current work intends to contribute in the characterization of the structural glycobiology and function of AGP by building a structural model of its fully glycosylated form, taking into account the different glycoforms that are found in vivo. The obtained data points to the absence of a major influence of glycosylation on AGP's secondary structure, in agreement with crystallography observations. However, the glycan chains seem able to interfere with the protein dynamics, mainly at the AGP-ligand-binding site, indicating a possible role in its complexation to drugs and other bioactive compounds. By examining the influence of fucosylation on AGP structure and binding to selectins, it is proposed that the latter may bind to glycan chains linked to Asn54 and Asn75, and that this binding may involve other glycans, such as the one attached to Asn15. These results point to an increased participation of carbohydrates on the observed AGP roles in pharmacokinetics and inflammation.

A rapid and simple approach for glycoform analysis

Fast glycoform analysis is important for quality control of glycoproteins that account for over 40% of the approved biopharmaceuticals. Herein, we realized an Au nanoparticle-based lectin affinity chromatography (LAC) using simple standard laboratory equipment for fast glycoform analysis. Pisum sativum agglutinin (PA), a lectin derived from P. sativum, was covalently conjugated to Au nanoparticles via naturally formed carboxylic groups onto the surface of Au nanoparticles and amino groups of PA. Each model glycoprotein was separated into several fractions including the unbound, weakly bound, modestly bound, and strongly bound glycoforms based on affinity strength of the glycoform toward PA. A single run of Au nanoparticle-based LAC was finished within 18 min, which could be further decreased by centrifuging the mixture of the PA functionalized Au nanoparticles and the glycoproteins at a higher speed. To our knowledge, we are the first to use Au nanoparticles as LAC matrix.

Statistical evaluation of CZE-UV and CZE-ESI-MS data of intact α-1-acid glycoprotein isoforms for their use as potential biomarkers in bladder cancer

α-1-acid glycoprotein (AGP) is a highly heterogeneous protein that presents a vast number of isoforms (molecules of the protein differing in its peptidic and/or glycosidic moieties). In the last years, several authors have studied the potential use of AGP as a cancer biomarker. These studies focus on the correlation of different features of AGP structure (i.e. fucosylation, antennarity) with cancer or on the total protein blood concentration. In this study, the potential of CZE-UV and CZE-ESI-MS analysis of intact AGP isoforms to study the correlation of this protein with bladder cancer is shown. Samples from 16 individuals (eight healthy, eight bladder cancer) were analyzed and characterized in great detail including data on intact protein isoforms and on released glycans. The analytical data were evaluated employing different statistical techniques (ANOVA; principal component analysis, PCA; linear discriminant analysis; and partial least squares-discriminant analysis). Statistical differences between the two groups of study were observed. The best results were obtained by linear discriminant analysis of the CZE-ESI-MS data for intact AGP isoforms (93.75% of correct classification). Due to MS characterization, it can be observed that differences between the samples are mainly due to higher abundance of AGP isoforms containing tri- and tetra-antennary fucosylated oligosaccharides in cancer patients. The results show the great potential of CE-MS in combination with advanced data processing for the use of intact protein isoforms as disease biomarkers.

CE-LIF-MS n profiling of oligosaccharides in human milk and feces of breast-fed babies

Mixtures of the complex human milk oligosaccharides (HMOs) are difficult to analyze and gastrointestinal bioconversion products of HMOs may complicate analysis even more. Their analysis, therefore, requires the combination of a sensitive and high-resolution separation technique with a mass identification tool. This study introduces for the first time the hyphenation of CE with an electrospray mass spectrometer, capable to perform multiple MS analysis (ESI-MS(n)) for the separation and characterization of HMOs in breast milk and feces of breast-fed babies. LIF was used for on- and off-line detections. From the overall 47 peaks detected in off-line CE-LIF electropherograms, 21 peaks could be unambiguously and 11 peaks could be tentatively assigned. The detailed structural characterization of a novel lacto-N-neo-tetraose isomer and a novel lacto-N-fucopentaose isomer was established in baby feces and pointed to gastrointestinal hydrolysis of higher-Mw HMOs. CE-LIF-ESI-MS(n) presents, therefore, a useful tool which contributes to an advanced understanding on the fate of individual HMOs during their gastrointestinal passage.

From micro to macro: conversion of capillary electrophoretic separations of biomolecules and bioparticles to preparative free-flow electrophoresis scale

This invited contribution in the special issue of Electrophoresis published in celebration of the 30th Anniversary of this journal reflects the impact of our milestone paper [Prusík, Z., Kasicka, V., Mudra, P., Stepánek, J., Smékal, O., Hlavácek, J., Electrophoresis 1990, 11, 932-936] in the area of conversion of microscale analytical and micropreparative CE separations of biomolecules and bioparticles into (macro)preparative free-flow electrophoresis (FFE) scale on the basis of a correlation between CE and FFE methods. In addition to the survey of advances in the relatively narrow field of CE-FFE correlation and CE-FFE conversion, a comprehensive review of the recent developments of micropreparative CE and (macro)preparative FFE techniques is also presented and applications of these techniques to micro- and (macro)preparative separations and purifications of biomolecules and bioparticles are demonstrated. The review covers the period since the year of publication of the above paper, i.e. ca. the last 20 years.

Capillary lectin-affinity electrophoresis for glycan analysis

Glycosylation is one of the most important post-translational events for proteins, affecting their functions in health and disease, and plays significant roles in various information trafficking for intercellular and intracellular biological events. The glycans which show such important effects are generally present as quite complex mixtures in minute amounts. The approach described here makes it possible to profile glycans for the analysis of post-translational modification of proteins with carbohydrates. The method is based on high-resolution separation of fluorescent-labeled carbohydrates by capillary electrophoresis with laser-induced fluorescent detection in the presence of carbohydrate-binding proteins at different concentrations. The technique affords simultaneous determination of glycans having similar structures even in complex mixtures.

Enrichment strategies for glycopeptides

In order to understand glycoprotein functionality, information on the structure of both the core proteins and the glycan moieties is necessary. From a practical viewpoint, glycopeptides rather than whole glycoproteins are the general targets for structural analysis, which is primarily carried out by employing mass spectrometry (MS). Using the "glycoproteomics" concept, several techniques have recently been developed to allow the preparation of a series of reference glycopeptides. In this chapter, we describe two selective capturing methods for glycopeptides, i.e., lectin-affinity chromatography and polysaccharide hydrophilic affinity physicochemical chromatography. The combined use of these methods effectively removes non-glycosylated peptides, the inclusion of which substantially interferes with glycopeptide ionization in MS analysis.

Capillary electrophoresis-electrospray ionization mass spectrometry for rapid and sensitive N-glycan analysis of glycoproteins as 9-fluorenylmethyl derivatives

It is well known that most protein therapeutics such as monoclonal antibody pharmaceuticals and other biopharmaceuticals including cancer biomarkers are glycoproteins, and thus the development of high-throughput and sensitive analytical methods for glycans is essential in terms of their determination and quality control. We previously reported a novel alternative labeling method for glycans involving 9-fluorenylmethyl chloroformate (Fmoc-Cl) instead of the conventional reductive amination procedure. The derivatives were analyzed by high-performance liquid chromatography (HPLC) (Kamoda S, Nakano M, Ishikawa R, Suzuki S, Kakehi K. 2005. Rapid and sensitive screening of N-glycans as 9-fluorenylmethyl derivatives by high-performance liquid chromatography: A method which can recover free oligosaccharides after analysis. J Proteome Res. 4:146-152). This method was rapid and simple; however, it was time-consuming in terms of analysis by HPLC and did not provide so much information such as the detailed structures and mass numbers of glycans. Here we have developed a high-throughput and highly sensitive method. It comprises three steps, i.e., release of glycans, derivatization with Fmoc, and capillary electrophoresis-electrospray ionization mass spectrometry (CE-ESI MS) analysis. We analyzed several glycoproteins such as fetuin, alpha1 acid glycoprotein, IgG, and transferrin in order to validate this method. We were able to analyze the above glycoproteins with the three-step procedure within only 5 h, which provided detailed N-glycan patterns. Moreover, the MS/MS analysis allowed identification of the N-glycan structures. As novel applications, the method was employed for the analysis of N-glycans derived from monoclonal antibody pharmaceuticals and also from alpha-fetoprotein; the latter is known as one of the tumor markers of hepatocellular carcinomas. We were able to easily and rapidly determine the detailed structures of the N-glycans. The present method is very useful for the analysis of large numbers of samples such as a routine analysis.

Glycosylation analysis of glycoproteins and proteoglycans using capillary electrophoresis-mass spectrometry strategies

This review highlights recent developments in glycosylation analysis by modern MS in combination with CE based preseparation. Focused on CE-MS strategies aimed for glycotyping, the review addresses the detailed glycoform analysis of glycoproteins, glycopeptides, and proteoglycans. Glycoform analysis in the context of modern glycoproteomics is briefly addressed, as well. CZE, CIEF, and frontal analysis CE approaches hyphenated to high-resolution multistage MS for the detailed analysis of protein-linked glycan structures are overviewed in a comprehensive way. Advantages and limitations of various methodological approaches and techniques as well as mass spectrometric instrumentation are discussed in the particular context of glycoanalysis.

Mass spectrometric and linear discriminant analysis of N-glycans of human serum alpha-1-acid glycoprotein in cancer patients and healthy individuals

N-glycan oligosaccharides of human serum alpha(1)-acid glycoprotein (AGP) samples isolated from 43 individuals (healthy individuals and patients with lymphoma and with ovarian tumor) were analyzed by MALDI-TOF mass spectrometry and a multivariate statistical method (linear discriminant analysis, LDA). 34 different glycan structures have been identified. From the glycosylation pattern determined by mass spectrometry fucosylation and branching indices have been calculated. These parameters show only small differences between the patient groups studied, but these differences are not sufficiently large to use as a potential biomarker. LDA analysis, on the other hand shows a very good separation between the three groups (with a classification of 88%). Cross-validation indicates that the method has predictive power: Identifying cancerous vs. healthy individuals shows 96% selectivity and 93% specificity; identification of lymphoma vs. the mixed group of healthy and ovarian tumor cases is also promising (72% selectivity and 84% specificity). The pilot study presented here demonstrates that mass spectrometry combined with linear discriminant analysis (LDA) may provide valuable data for identifying and studying the pathophysiology of malignant diseases.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update covering the period 2001-2002

This review is the second update of the original review on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates that was published in 1999. It covers fundamental aspects of the technique as applied to carbohydrates, fragmentation of carbohydrates, studies of specific carbohydrate types such as those from plant cell walls and those attached to proteins and lipids, studies of glycosyl-transferases and glycosidases, and studies where MALDI has been used to monitor products of chemical synthesis. Use of the technique shows a steady annual increase at the expense of older techniques such as FAB. There is an increasing emphasis on its use for examination of biological systems rather than on studies of fundamental aspects and method development and this is reflected by much of the work on applications appearing in tabular form.

CZE of human alpha-1-acid glycoprotein for qualitative and quantitative comparison of samples from different pathological conditions

Alpha-1-acid glycoprotein (AGP) presents different forms, which may arise from differences in the amino acid sequence and/or in the glycosidic part of the protein. Changes in forms of AGP have been described in literature as a possible tumor marker. While most previous works have approached the study of glycopeptides and/or glycans obtained after fragmentation of the protein, in this work, a CZE method is developed to separate up to eleven peaks of intact forms of AGP. A computer program developed in our laboratory is used to select the migration parameters that make possible an accurate assignment of AGP peaks. Electropherograms of AGP samples purified from sera of cancer patients and healthy donors are qualitatively and quantitatively compared. Percentages of correct assignment of AGP peaks close to 100% are achieved by using either the migration time of each peak relative to that of the EOF marker or the effective electrophoretic mobility of the peaks. The computer program permits to select, among different hypotheses for peak allotment, that one providing the highest accuracy of assignment. In this way, some peaks with different charge-to-mass ratio and a different distribution of area percentage of AGP forms are observed when comparing samples from sick and healthy individuals. Thus, a method that permits to compare AGP forms existing in sera of individuals with different pathophysiological situations has been developed. A potential for using AGP forms analyzed by CZE as a disease marker and for using this technique for screening purposes is envisaged.

Capillary electrophoresis for the analysis of glycoprotein pharmaceuticals

Carbohydrate chains in glycoprotein pharmaceuticals play important roles for the expression of their biological activities, but the structure and compositions of carbohydrate chains are dependent on the conditions for their production. Therefore, evaluation of the carbohydrate chains is quite important for productive process development, characterization of product for approval application, and routine quality control. The oligosaccharides themselves have complex structure including blanching and various glycosidic linkages, and oligosaccharides in one glycoprotein pharmaceutical generally have high heterogeneity, and characterization of oligosaccharide moiety in glycoprotein has been a challenging target. In these situations, CE has been realized as a powerful tool for oligosaccharide analysis due to its high resolution and automatic operating system. This review focuses on the application of CE to the glycoform analysis of glycoproteins and profiling of the N-linked glycans released from glycoprotein pharmaceuticals. Current applications for structure analysis using CE-MS(n) technique and glycan profiling method for therapeutic antibody are also described.

Comparative studies on the analysis of urinary trypsin inhibitor (ulinastatin) preparations

Urinary trypsin inhibitor (ulinastatin) is a characteristic protein pharmaceutical which contains both glycosaminoglycans and N-linked glycans in its molecule and has been used for treatment of acute pancreatitis. The comparability of ulinastatin preparations of different lots or from different companies was studied by using conventional analytical approaches such as SDS-PAGE, cellulose acetate membrane electrophoresis, and HP size-exclusion chromatography (SEC) and also by using newly developed techniques such as CE and MALDI-TOF MS. The methods using SEC and SDS-PAGE according to The Japanese Pharmacopoeia showed similar molecular masses for two different preparations, and the estimated molecular masses were significantly different from those observed with MALDI-TOF MS. We also showed that the electrophoretic methods using cellulose acetate membrane electrophoresis and CE can be used for comparability assessments of ulinastatin preparations. In addition, we analyzed the unsaturated disaccharides derived from glycosaminoglycan (chondroitin 4-sulfate chain) and N-linked oligosaccharides attached to ulinastatin by CE after releasing them by enzymatic digestion followed by fluorescent labeling with 2-aminoacridone and 2-aminobenzoic acid, respectively. The results indicated that carbohydrate chains are important as markers for comparability assessments of ulinastatin pharmaceutical preparations.

Capillary electrophoresis-based separation techniques for the analysis of proteins

CE offers the advantages of high speed, great efficiency, as well as the requirement of minimum amounts of sample and buffer for the analysis of proteins. In this review, we summarize the CE-based techniques coupled with absorption, LIF, and MS detection systems for the analysis of proteins mostly within the past 5 years. The basic principle of each technique and its advantages and disadvantages for protein analysis are discussed in brief. Advanced CE techniques, including on-column concentration techniques and high-efficiency multidimensional separation techniques, for high-throughput protein profiling of complex biological samples and/or of single cells are emphasized. Although the developed techniques provide improved peak capacity, they have not become practical tools for proteomics, mainly because of poor reproducibility, low-sample lading capacity, and low throughput due to ineffective interfaces between two separation dimensions and that between separation and MS systems. In order to identify the complexities and dynamics of the proteomes expressed by cells, tissues, or organisms, techniques providing improved analytical sensitivity, throughput, and dynamic ranges are still demanded.

Rapid analysis of oligosaccharides derived from glycoproteins by microchip electrophoresis

A novel method for fast profiling of complex oligosaccharides released from glycoproteins based on microchip electrophoresis (mu-CE) is presented here. The characterization of separation conditions, i.e., the composition, concentration and pH of running buffer as well as the applied voltage, has been performed using maltose (G2), cellobiose ( G2'), maltriose (G3) and panose (G3') as oligosaccharide isomer models. In mu-CE, much better separation of oligosaccharide isomers and oligosaccharide ladder was obtained in phosphate buffer than in borate buffer over a wide pH range. Under optimal conditions, high-performance separation of the N-linked complex oligosaccharides released from ribonuclease B, fetuin, alpha1-acid glycoprotein (AGP) and IgG was achieved using polymethylmethacrylate (PMMA) microchips with an effective separation channel of 30 mm. These results represent the first reported analysis of the N-linked oligosaccharides derived from glycoproteins by mu-CE, indicating that the present mu-CE-based method is a promising alternative for characterization of the N-linked oligosaccharides in glycoproteins.

Analysis of glycoprotein-derived oligosaccharides in glycoproteins detected on two-dimensional gel by capillary electrophoresis using on-line concentration method

Capillary electrophoresis (CE) is an effective tool to analyze carbohydrate mixture derived from glycoproteins with high resolution. However, CE has a disadvantage that a few nanoliters of a sample solution are injected to a narrow capillary. Therefore, we have to prepare a sample solution of high concentration for CE analysis. In the present study, we applied head column field-amplified sample stacking method to the analysis of N-linked oligosaccharides derived from glycoprotein separated by two-dimensional gel electrophoresis. Model studies demonstrated that we achieved 60-360 times concentration effect on the analysis of carbohydrate chains labeled with 3-aminobenzoic acid (3-AA). The method was applied to the analysis of N-linked oligosaccharides from glycoproteins separated and detected on PAGE gel. Heterogeneity of alpha1-acid glycoprotein (AGP), i.e. glycoforms, was examined by 2D-PAGE and N-linked oligosaccharides were released by in-gel digestion with PNGase F. The released oligosaccharides were derivatized with 3-AA and analyzed by CE. The results showed that glycoforms having lower pI values contained a larger amount of tetra- and tri-antennary oligosaccharides. In contrast, glycoforms having higher pI values contained bi-antennary oligosaccharides abundantly. The result clearly indicated that the spot of a glycoprotein glycoform detected by Coomassie brilliant blue staining on 2D-PAGE gel is sufficient for quantitative profiling of oligosaccharides.

Circular dichroism and absorption spectroscopic data reveal binding of the natural cis-carotenoid bixin to human α1-acid glycoprotein

Using circular dichroism (CD) and electronic absorption spectroscopy techniques, interaction of the natural dietary cis-carotenoid bixin with an important human plasma protein in vitro was demonstrated for the first time. The induced CD spectra of bixin obtained under physiological conditions (pH 7.4, 37 degrees C) revealed its binding to the serum acute-phase reactant alpha(1)-acid glycoprotein (AGP), a member of the lipocalin protein family. Spectral features of the extrinsic Cotton effects of bixin suggested the inclusion of a single, chirally distorted ligand molecule into the asymmetric protein environment. Compared with the absorption spectra obtained in ethanol and benzene, the strong red shift of the main absorption peak of AGP-bound bixin indicated that the proposed binding site was rich in aromatic residues, and also suggested that hydrophobic interactions were involved in the binding. Using the data obtained from the CD titration experiments, the association constant (Ka=4.5x10(5)M-1) and stoichiometry of the binding (0.15) were calculated. The low value of the stoichiometry was attributed to the structural polymorphism of AGP. To the authors' knowledge, the current study represents the first human lipocalin protein for which carotenoid binding affinity has been explored in vitro with these techniques.

Resolution of N-linked oligosaccharides in glycoproteins based upon transglycosylation reaction by CE-TOF-MS

The resolution of asparagine-type oligosaccharides in glycoproteins was carried out by combination of the transglycosylation reaction and CE-TOF-MS. The oligosaccharides enzymatically transferred to a fluorescent acceptor (NDA-Asn-GlcNAc) with Endo-M. The resulting fluorescent-oligosaccharides were separated by CE and detected by TOF-MS. Disialo-Asn was successfully identified by the proposed procedure. Application to oligosaccharides in ovalbumin was also described in this communication.

Separation and detection methods for covalent drug–protein adducts

Covalent binding of reactive metabolites of drugs to proteins has been a predominant hypothesis for the mechanism of toxicity caused by numerous drugs. The development of efficient and sensitive analytical methods for the separation, identification, quantification of drug-protein adducts have important clinical and toxicological implications. In the last few decades, continuous progress in analytical methodology has been achieved with substantial increase in the number of new, more specific and more sensitive methods for drug-protein adducts. The methods used for drug-protein adduct studies include those for separation and for subsequent detection and identification. Various chromatographic (e.g., affinity chromatography, ion-exchange chromatography, and high-performance liquid chromatography) and electrophoretic techniques [e.g., sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), two-dimensional SDS-PAGE, and capillary electrophoresis], used alone or in combination, offer an opportunity to purify proteins adducted by reactive drug metabolites. Conventionally, mass spectrometric (MS), nuclear magnetic resonance, and immunological and radioisotope methods are used to detect and identify protein targets for reactive drug metabolites. However, these methods are labor-intensive, and have provided very limited sequence information on the target proteins adducted, and thus the identities of the protein targets are usually unknown. Moreover, the antibody-based methods are limited by the availability, quality, and specificity of antibodies to protein adducts, which greatly hindered the identification of specific protein targets of drugs and their clinical applications. Recently, the use of powerful MS technologies (e.g., matrix-assisted laser desorption/ionization time-of-flight) together with analytical proteomics have enabled one to separate, identify unknown protein adducts, and establish the sequence context of specific adducts by offering the opportunity to search for adducts in proteomes containing a large number of proteins with protein adducts and unmodified proteins. The present review highlights the separation and detection technologies for drug-protein adducts, with an emphasis on methodology, advantages and limitations to these techniques. Furthermore, a brief discussion of the application of these techniques to individual drugs and their target proteins will be outlined.

Sample clean-up method for analysis of complex-type N-glycans released from glycopeptides

N-Glycans in glycoprotein can be liberated either from glycoproteins or from their glycopeptides with glycoamidases. The latter approach is preferable, because it requires a smaller amount of the enzyme, and yields N-glycans in excellent yields. Moreover it alleviates the necessity of removing from the reaction mixture the detergents needed to denature the glycoproteins. On the other hand, this approach necessitates removal of interfering peptidic materials, because some of the peptide peaks often overlap with the peaks of carbohydrate chains in high-performance anion-exchange chromatography (HPAEC). These peptidic materials also hinder labeling of N-glycans by reductive amination. We have tried to remove the interfering peptidic materials by several different methods--octadecyl (C18) silica cartridge, cation-exchange resin column, and graphitized carbon cartridge. Unfortunately, none of these could completely remove the interfering peptidic materials. Therefore, we resorted to modify the amino groups of the peptidic materials with sodium 2,4,6-trinitro-benzene-1-sulfonate (TNBS) to render them more hydrophobic, so that they can be retained more strongly on the C18 or graphitized carbon cartridges. In the model study presented here, we were able to obtain N-glycans for HPAEC analyses without any interfering materials by a combination of TNBS reaction and graphitized carbon treatment.

Improved capillary electrophoretic separation and mass spectrometric detection of oligosaccharides

We have developed a CE method for the separation of structural isomers of oligosaccharides labeled with N-quaternized benzylamine. Oligosaccharides with reducing ends were derivatized with benzylamine by reductive amination followed by quaternization to yield a fixed cation label. The benzylamine-derivatized oligosaccharides were analyzed by CE-UV in ammonium acetate buffer and off-line matrix-assisted laser desorption ionization (MALDI) MS. The method was applied to a 1 nmol sample of a model oligosaccharide (LNDFH 1). From this sample a 38 fmol diluted standard was detected. The quaternization of benzylamine-labeled products significantly improved CE separation of neutral oligosaccharides along with several structural isomers. Two hexasaccharide isomers (LNDFH I and LNDFH II) were baseline resolved using an ammonium acetate buffer. This method was also applied successfully to the profiling of oligosaccharides released from the glycoprotein RNase B. The release of 6 pmol of glycans followed by workup showed the detection of all components, with one component corresponding to 100 fmol. Micropreparative collection of CE enabled successful off-line CE-MALDI-MS without additional sample clean up. This report provides a simple and rapid method to separate and analyze oligosaccharides.