Comparison of CE-MS and LC-MS Analyses of Avian Eggshell Matrix Proteins

CE-MS and HPLC-MS methods were developed and compared for the analysis of insoluble proteins in an avian eggshell matrix. The eggshell was gradually decalcified to obtain four distinct layers (cuticle, two palisade and a mammillary layer). The insoluble proteinaceous films from these layers were chemically and/or enzymatically splitted with CNBr/trypsin and proteinase K. The generated peptides were separated by CE and HPLC on-line coupled to MS detection. Capillary electrophoresis (CE) was coupled to an ion-trap electrospray ionization mass spectrometer (Agilent LC-MSD Trap XCT-Ultra) using a grounded needle carrying a flow of sheath liquid (5 mM ammonium acetate/2-propanol, 1:1, at flow-rate 3 μL min⁻¹). Five main proteins were identified: ovocleidin-116, ovocalyxin-32, ovocalyxin-36, ovocleidin-17 and ovalbumin. The distribution of these proteins in the eggshell was found to be dependent on the location/layer. In the outermost layer (the cuticle layer) the dominant protein is ovocalyxin-32; ovocleidin-116 is distributed throughout all layers while ovalbumin is present only in the internal mammillary layer. The CE-MS peptide maps of eggshell proteins were compared to the HPLC-MS ones, and a different mechanism of separation (migration/elution order) was demonstrated for both methods.

     

Determination of insoluble avian eggshell matrix proteins

The organic components of bones and other mineralized tissues have a high impact on the organization and deposition of calcium, and consequently influence the mechanical properties of those tissues. The extractable proteins of avian eggshells have been studied extensively and many of them have been identified; insoluble (non-extractable) proteins have been sparsely studied, however. In the work discussed in this paper we studied EDTA-insoluble proteins by gradual decalcification of eggshell with EDTA. The insoluble proteinaceous films were chemically treated with cyanogen bromide and the mixtures of large fragments obtained were gradually precipitated with salt. The separated fractions were digested with trypsin and analyzed by HPLC–MS–MS (ion trap mass spectrometer). Analysis of the entire eggshell matrix (without precipitation steps) only enabled 6 proteins to be determined (ovocalyxins 32 and 36, ovocleidin 17 and 116, clusterin, and ovalbumin). Pretreatment of the individual eggshell layers and gradual precipitation with salt markedly increased the number of proteins identified – 28 proteins were determined. We identified for the first time collagens I (two chains) and III in the eggshell matrix, and Kunitz-like protease inhibitor as a major shell matrix protein. Besides the above mentioned proteins we can also mention EDIL3, fibronectin, sulfhydryl oxidase, tubulin alpha 1, lysozyme, Dickkopf-related protein 3, keratins, and ovotransferrin. The relative abundances of proteins in all eggshell layers were determined using the exponentially modified protein abundance index (emPAI). In the cuticle layer seven proteins were identified, whereas 16 proteins were described in the palisade layer and 23 in the mammillary layer.     

Insoluble eggshell matrix proteins--their peptide mapping and partial characterization by capillary electrophoresis and high-performance liquid chromatography

Avian eggshell matrix proteins were studied by two analytical approaches. Peptide mapping was done by trypsin and pepsin followed by collagenase cleavage; analyses were carried out by capillary electrophoresis and reversed-phase high-performance liquid chromatography (HPLC). Comparison of peptide maps obtained by both methods revealed a complex mixture of peptides in the insoluble layers of the eggshell; it was concluded that there are at least three different insoluble protein/peptide layers in the avian eggshell (cuticle, palisade, and mammillary layer). Partial characterization of peptides in each layer was made by HPLC-mass spectrometry analysis. There is an evidence that the eggshell insoluble proteins contain species susceptible to collagenase cleavage, however, the sequences split by this enzyme probably are not those typical for the main triple-helical core of collagenous proteins. It is proposed that the action of collagenase upon eggshell proteins is caused by the side effect of collagenase described previously with synthetic peptides. Some of the proteins present are probably glycosylated. Fatty acid content in the insoluble eggshell layers (after decalcification) was in the range of 2-4% (which reflected both lipid and lipoproteins bound fatty acids). Porphyrin pigments are dominant in the cuticle layer.     

Proteomic analysis of chicken eggshell cuticle membrane layer

The eggshell is a barrier that plays an important role in the defense of the egg against microbial and other infections; it protects the developing bird against unfavorable impacts of the environment and is essential for the reproduction of birds. The avian eggshell is a complex structure that is formed during movement along the oviduct by producing a multilayered mineral-organic composite. The extractable proteins of avian eggshells have been studied extensively and many of them identified, however, the insoluble (non-extractable) proteins have been sparsely studied. We studied the EDTA-insoluble proteinaceous film from the cuticle layer of eggshell. This film consists of three main areas: spots (cca 300 μm diameter), blotches (small spots with diameter only tens of μm), and the surroundings (i.e., the area without spots and blotches) where spots contain a visible accumulation of pigment. These areas were cut out of the membrane by laser microdissection, proteins were cleavaged by trypsin, and the peptides were analyzed by nLC/MS (Q-TOF). This study has identified 29 proteins and a further eight were determined by less specific “cleavage” with semitrypsin. The relative abundances of these proteins were determined using the exponentially modified protein abundance index (emPAI) where the most dominant proteins were eggshell-specific ones, such as ovocleidin-17 and ovocleidin-116. Individual areas of the cuticle membrane differ in their relative proportions of 14 proteins, where significant differences between the three quantification criteria (direct, after normalization to ovocledin-17, or to ovocledin-116) were observed in four proteins.     

Study of posttranslational non-enzymatic modifications of collagen using capillary electrophoresis/mass spectrometry and high performance liquid chromatography/mass spectrometry

The depository effects that occur in slowly metabolized proteins (typically glycation) are very difficult to assess, owing to their extremely low concentration in the protein matrix. Collagen accumulates reactive metabolites through reactions that are not regulated by enzymes. A typical example of these non-enzymatic changes is glycation (the Maillard reaction, the formation of advanced glycation end products), resulting from the reaction of the oxo-group of sugars with the epsilon-amino group of lysine and arginine. Collagen samples (type I) as a test protein were incubated separately with glucose, ribose and malondialdehyde. Collagen was fragmented with cyanogen bromide and then digested with trypsin. This peptide digest was separated by CE, CE-MS/MS, and HPLC-MS/MS. An ion trap MS was used and MS conditions were optimized for both methods. These on-line CE-MS/MS and HPLC-MS/MS couplings made it possible to discover specific modifications such as (N(epsilon)-(carboxymethyl)-lysine) in the precise location in the structure of collagen corresponding to posttranslational non-enzymatic modifications. A new CE-MS/MS technique for peptide analysis was developed, and applied in the identification of posttranslational modifications in slowly metabolized test proteins.     

Capillary electrophoresis-mass spectrometry for the analysis of intact proteins 2007-2010

CE coupled to MS has proven to be a powerful analytical tool for the characterization of intact proteins, as it combines the high separation efficiency of CE with the selectivity of MS. This review provides an overview of the development and application of CE-MS methods within the field of intact protein analysis as published between January 2007 and June 2010. Ongoing technological developments with respect to CE-MS interfacing, capillary coatings for CE-MS, coupling of CIEF with MS and chip-based CE-MS are treated. Furthermore, CE-MS of intact proteins involving ESI, MALDI and ICP ionization is outlined and overviews of the use of the various CE-MS methods are provided by tables. Representative examples illustrate the applicability of CE-MS for the characterization of proteins, including glycoproteins, biopharmaceuticals, protein-ligand complexes, biomarkers and dietary proteins. It is concluded that CE-MS is a valuable technique with high potential for intact protein analysis, providing useful information on protein identity and purity, including modifications and degradation products.     

Determination of drug residues in water by the combination of liquid chromatography or capillary electrophoresis with electrospray mass spectrometry

Methods for the determination of drug residues in water have been developed based on the combination of liquid chromatography (LC) or capillary electrophoresis (CE) with mass spectrometry (MS). For HPLC-MS two types of interfaces (pneumatically assisted electrospray ionization interface or an atmospheric pressure chemical ionization interface, respectively) were employed and compared in terms of detection limits. 2 mM Ammonium acetate at pH 5.5 and a methanol gradient was used for the HPLC-MS allowing the separation of a number of drugs such as paracetamol, clofibric acid, penicillin V, naproxen, bezafibrate, carbamazepine, diclofenac, ibuprofen and mefenamic acid. A 20 mM ammonium acetate solution, pH 5.1 was employed for the separation of clofibric acid, naproxen, bezafibrate, diclofenac, ibuprofen and mefenamic acid by CE-MS. Sample pretreatment was performed by solid-phase extraction (SPE) for HPLC-MS or by a combination of liquid-liquid extraction and SPE for CE-MS. The applicability of both the HPLC-MS and CE-MS method was demonstrated for several river water samples.     

毛细管电泳-质谱联用技术及其在蛋白质组学中的应用

蛋白质组学研究在生物学、精准医学等方面发挥着重要的作用。然而研究面临的巨大挑战来自生物样品的复杂性,因此在质谱（MS）鉴定技术不断革新的同时,发展分离技术以降低样品复杂度尤为重要。毛细管电泳（CE）技术具有上样体积小、分离效率高、分离速度快等优势,其与质谱的联用在蛋白质组学研究中越来越受到关注。低流速鞘流液和无鞘流液接口的发展及商品化推动了CE-MS技术的发展。目前毛细管区带电泳（CZE）、毛细管等电聚焦（CIEF）、毛细管电色谱（CEC）等分离模式已与质谱联用,其中CZE-MS应用最广泛。目前被广泛采用的蛋白质组学研究策略主要是基于酶解肽段分离鉴定的"自下而上（bottom-up）"策略。首先,CE-MS技术对酶解肽段的检测灵敏度高达1 zmol,已成功应用于单细胞蛋白质组学;其次,毛细管电泳技术与反相液相色谱互补,为疏水性质相近的肽段（尤其是翻译后修饰肽段）的分离鉴定提供了新的途径。基于整体蛋白质分离鉴定的自上而下"top-down"策略可以直接获得更精准、更完整的蛋白质信息。CE技术在蛋白质大分子的分离方面具有分离效率高、回收率高的优势,其与质谱的联用提高了整体蛋白质的鉴定灵敏度和覆盖度。非变性质谱（native MS）是一种在近生理条件下从完整蛋白质复合物水平上进行分析的质谱技术。CE与非变性质谱联用已被尝试用于蛋白质复合体的分离鉴定。该文引用了与CE-MS和蛋白质组学应用相关的93篇文献,综述了以上介绍的CE-MS的研究进展以及在蛋白质组学分析中的应用优势,并总结和展望了其应用前景。     

Comparison of high-performance liquid chromatography — Mass spectroscopy and capillary electrophoresis— mass spectroscopy for the analysis of phenolic compounds in diethyl ether extracts of red wines

Summary Reversed-phase high-performance liquid chromatography-mass spectroscopy (HPLC-MS) and capillary electrophoresis-mass spectroscopy (CE-MS) have been compared for the analysis of phenolic compounds in diethyl ether extracts of red wines. MS was performed in the electrospray negative-ionization mode. Despite the much higher separation efficiency of CE compared with LC, LC-MS furnishes far superior information for elucidation of the structure of the constituents. LC-MS enabled the identification of twenty-four compounds whereas only thirteen were characterized by CE-MS.     

Capillary electrophoresis-mass spectrometry for the analysis of intact proteins

Developments in the fields of protein chemistry, proteomics and biotechnology have increased the demand for suitable analytical techniques for the analysis of intact proteins. In 1989, capillary electrophoresis (CE) was combined with mass spectrometry (MS) for the first time and its potential usefulness for the analysis of intact (i.e. non-digested) proteins was shown. This article provides an overview of the applications of CE-MS within the field of intact protein analysis. The principles of the applied CE modes and ionization techniques used for CE-MS of intact proteins are shortly described. It is shown that separations are predominantly carried out by capillary zone electrophoresis and capillary isoelectric focusing, whereas electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) are the most popular ionization techniques used for interfacing. The combination of CE with inductively coupled plasma (ICP) MS for the analysis of metalloproteins is also discussed. The various CE-MS combinations are systematically outlined and tables provide extensive overviews of the applications of each technique for intact protein analysis. Selected examples are given to illustrate the usefulness of the CE-MS techniques. Examples include protein isoform assignment, single cell analysis, metalloprotein characterization, proteomics and biomarker screening. Finally, chip-based electrophoresis combined with MS is shortly treated and some of its applications are described. It is concluded that CE-MS represents a powerful tool for the analysis of intact proteins yielding unique separations and information.     

Mass Spectrometric and Contactless Conductivity Detection Approaches in the Determination of Muscle Relaxants by Capillary Electrophoresis

Novel and rapid capillary electrophoresis-coupled tandem mass spectrometry (CE-MS/MS) and capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C⁴D) methods have been developed for the separation and determination of three neuromuscular blocking agents: pancuronium, vecuronium, and rocuronium. In both cases, the separation was conducted in background electrolytes based on acidic acetate-ammonium buffers to avoid possible decomposition of the analytes that are known to be unstable in alkaline media. Baseline resolution of the analytes was achieved in the presence of modified γ-cyclodextrin by CE with C⁴D detection. The two detection techniques were compared with regard to analytical figures of merit including linear dynamic range, limit of detection, limit of quantification, precision, and accuracy. The calibration curves showed good linearity for both detection methods examined (characterized by r² ≥ 0.9908). The LODs of the CE-MS/MS and the CE-C⁴D methods differed at least by two orders of magnitude considering all analytes. The differences in precision and accuracy of these methods were evaluated and discussed. The assays of pancuronium, vecuronium, and rocuronium in commercial injection solutions by CE-MS/MS and CE-C⁴D were performed and the results compared.     

Application of capillary electrophoresis/ electrospray ionization-mass spectrometry to subcellular proteomics of Escherichia coli ribosomal proteins

We introduce capillary electrophoresis-mass spectrometry (CE-MS) as an efficient means for the on-line separation and identification of protein mixtures. It was found that while CE/electrospray ionization (ESI)-MS analysis of whole-cell lysate was too complicated for the one-dimensional CE-MS analysis, the technique was useful for the analysis of protein mixtures of moderate complexity (approximately 50 intact proteins). CE/ESI-MS was applied to the subcellular proteomics of ribosomal Escherichia coli. 55 out of the 56 ribosomal proteins were detected with ease by using only approximately 3.4 ng of ribosomal proteins. In addition, it was found that the mass accuracy of the conventional MS (such as quadrupole ion traps) was good enough to identify many post-translational modifications of the intact proteins by simply comparing their measured average molecular weight with the average molecular weight predicted from gene banks.     

Separation and characterization of human high-density apolipoproteins using a nonaqueous modifier in capillary electrophoresis-mass spectrometry

The separation and characterization of human apolipoproteins and their isoforms was investigated using capillary electrophoresis (CE) in combination with mass spectrometry (MS). The focus of these analyses was the major protein constituents of plasma high-density lipoproteins, apolipoprotein A-I and A-II. Using aqueous buffers in CE, no separation between apolipoprotein A-I and A-II was observed. With the addition of 10-20% acetonitrile, however, the two species could be separated. Furthermore, multiple peaks for each of the apolipoprotein species were observed under these CE conditions. In order to identify and characterize the components, these separations were then coupled with online mass spectrometric detection (CE-MS). Our CE-MS results suggest that the multiple components observed in the acetonitrile-containing CE separation appear to be oxidized forms of the proteins in addition to native forms of the apolipoprotein A-I and A-II. These data are in agreement with previous reports that the methionine residues of the high-density lipoproteins (HDLs) are sensitive to oxidation, which in turn, alters their lipid binding characteristics and secondary structure. In addition to oxidized forms of the proteins, apolipoprotein A-II contained additional components, which varied in mass by 128 Da. The structural differences between these components were determined by proteolytic digestion and tandem MS. Using these techniques, we determined that these components were due to truncation of the C-terminal glutamine amino acid residue on apolipoprotein A-II. These results demonstrate that CE in combination with MS is a promising technique for screening and characterizing isomers of plasma apolipoproteins.     

Characterization of proteins from Spirulina platensis microalga using capillary electrophoresis-ion trap-mass spectrometry and capillary electrophoresis-time of flight-mass spectrometry

In this work, a new capillary electrophoresis-mass spectrometry (CE-MS) procedure is developed to analyze proteins in Spirulina platensis microalgae. It is demonstrated that a fine optimization of several separation parameters is essential in order to achieve suitable CE-MS analysis of these proteins in natural extracts from microalgae. Namely, optimization of the composition of the separation buffer, electrospray conditions, and washing routine between runs are required in order to obtain reliable and reproducible CE-MS analyses of the main proteins found in this microalga (namely, allophycocyanin-alpha chain, allophycocyanin-beta, c-phycocyanin-alpha, and c-phycocyanin-beta). The relative molecular mass of these biopolymers is determined using two different MS instruments coupled to CE, i.e., CE-ion trap-MS and CE-time of flight-MS (CE-TOF-MS). A comparison between the results obtained with both instruments is carried out. The high resolution of the TOF-MS enables the distinction of small modifications in proteins and, thus, a more accurate mass determination. Interestingly, molecular mass values obtained by both CE-MS procedures agree very well while these experimental values are only in partial agreement with those theoretically expected (i.e., genetically derived masses). Some protein modifications due to amino acids exchange induced by nucleotide codon mutations are proposed to explain this difference.     

Determination of bupivacaine and metabolites in rat urine using capillary electrophoresis with mass spectrometric detection

A method using capillary electrophoresis-mass spectrometry (CE-MS) was developed for the structural elucidation of bupivacaine and metabolites in rat urine. Prior to CE-MS analysis, solid-phase extraction (SPE) was used for sample cleanup and preconcentration purposes. Exact mass and tandem mass spectrometric (MS/MS) experiments were performed to obtain structural information about the unknown metabolites. Two instruments with different mass analyzers were used for mass spectrometric detection. A quadrupole time-of-flight (Q-TOF) and a magnetic sector hybrid instrument were coupled to CE and used for the analysis of urine extracts. Hydroxybupivacaine as well as five other isomerically different metabolites were detected including methoxylated bupivacaine.     

Comparison of different chiral selectors for the enantiomeric determination of amphetamine-type substances in human urine by solid-phase extraction followed by capillary electrophoresis-tandem mass spectrometry

The present study develops a method for the enantioseparation of a group of amphetamines and their metabolites in urine by CE coupled to MS/MS (CE-MS/MS). Amphetamines present a chiral center and thus two enantiomers, which is important from a toxicological point of view because they may have different pharmacokinetic and pharmacological properties. It is therefore essential to find suitable methods to distinguish both enantiomers. Today the use of CE is becoming more important in this field since, with the simple addition of a chiral selector to the background electrolyte, the enantioseparation can easily be achieved. However, when CE is coupled to MS, the use of volatile chiral selectors and compatible background electrolytes or other strategies such as the countercurrent migration approach are required to avoid contamination of the ion source from nonvolatile species. In the present study, we use the latter strategy to evaluate six different chiral selectors using CE-MS/MS. As a sample pre-treatment, two cationic-exchange sorbents—Oasis WCX and Oasis MCX—are compared for the urine pre-treatment. Using this method, it was possible to achieve the complete chiral separation of the amphetamines under study with detection limits ranging between 0.8 and 1.5 ng/mL and method quantification limits between 2.0 and 8.0 ng/mL. Matrix-matched calibration curves up to 150 ng/mL were used to cover the usual concentration ranges at which amphetamines have generally been found in toxicological and forensic analyses.     

CE-MS of zein proteins from conventional and transgenic maize

In this work, an original CE-MS method has been developed to analyze the complex zein protein fractions from maize. A thorough optimization of: (i) zein protein extraction, (ii) CE separation, and (iii) electrospray-MS (ESI-MS) detection is carried out in order to obtain highly informative CE-MS profiles of this fraction. The developed CE-MS method provides good separation of multiple zein proteins based on their electrophoretic mobilities as well as adequate characterization of these proteins based on their M(r). Zein proteins with small M(r) differences (below 100 Da) were easily separated and successfully analyzed by CE-MS. Thus, apart of the so-called 15-kDa-beta-zein and 16-kDa-gamma-zein, which are demonstrated to be formed by a heterogeneous group of proteins, numerous alpha-zeins belonging to the 19- and 22-kDa fraction were also identified for the first time in this work. The usefulness of this CE-MS method was corroborated by comparing the zein-protein fingerprints of various maize lines including transgenic and their corresponding nontransgenic isogenic lines cultivated under the same conditions.     

2020年毛细管电泳技术年度回顾

该文为2020年毛细管电泳(capillary electrophoresis,CE)技术年度回顾.归纳总结了以"capillary electro-phoresis-mass spectrometry"或"capillary isoelectric focusing"或"micellar electrokinetic...     

Amino acid analysis of dried blood spots for diagnosis of phenylketonuria using capillary electrophoresis-mass spectrometry equipped with a sheathless electrospray ionization interface

We describe a capillary electrophoresis-mass spectrometry (CE-MS) method for newborn screening of a representative amino acid metabolic disease, namely, phenylketonuria (PKU). Underivatized phenylalanine and tyrosine in a dried blood spot (DBS) were simultaneously determined by CE-MS equipped with an ionophore membrane-packed sheathless electrospray ionization interface, which was developed by our group. The method was optimized for rapid determination of the underivatized amino acids, phenylalanine and tyrosine extracted from a DBS. Under the optimized conditions, the limit of detection of phenylalanine and tyrosine (signal-to-noise ratio, 3) was 0.03 and 0.07 mg/L in DBS, respectively, with a CE run time of less than 3 min. For repeated runs of a sample, coefficients of variation (CVs) for migration time were less than 3.7 %, whereas CVs for the area ratio under the curve were 2.1 and 2.9 % for 20 consecutive runs of 49.5 mg/kg Phe and 36.2 mg/kg Tyr, respectively. However, the relative standard deviations of intra- and interday assays for DBS samples were <6.2 and <5.8 %, respectively, which were substantially due to sample extraction from DBS. The analytical method was applied to real clinical samples of Korean neonates, and results were compared with those of conventional methods for PKU diagnosis, which required reference analytical methods such as isotope dilution CE-MS or high-performance liquid chromatography-mass spectrometry for quality assurance of the conventional kit-based assays. The distinct advantages of high sensitivity and extremely low sample volume, as well as a simple, easy, and economic sample pretreatment, were demonstrated for the proposed method.     

Applicability of predictive models to the peptide mobility analysis by capillary electrophoresis-electrospray mass spectrometry

The prediction of peptide mobility by capillary electrophoresis (CE) coupled to electrospray mass spectrometry (MS) is studied in order to verify the validity of the semi-empirical models developed in classical CE. This work relies on the experimental determination of the electrophoretic mobilities of 68 peptides, different in charge and in size. The results indicate that the prediction is possible in CE-MS experiments, in spite of the restraints inherent in the coupling conditions. The best fit of experimental data was obtained with the Offord's model. The efficiency of the model was confirmed by the analysis of a peptide mixture in CE-MS.