Allergenic compounds on the inner and outer surfaces of natural latex gloves: MALDI mass spectrometry and imaging of proteinous allergens

Natural latex gloves are the cause of a severe health problem to an increasing number of healthcare workers or patients due to the presence of protein allergens as Hevein or Rubber Elongation Factor (REF). One of the most challenging problems is the in situ localization of theses allergens in, e.g. gloves, to estimate the allergenic potential of the latex material. A sample preparation protocol applying a binary matrix-assisted laser desorption/ionization(MALDI) matrix containing alpha-cyano-4-hydroxy cinnamic acid (CHCA) and 2,5-dihydroxy benzoic acid (DHB) on trifluoro acetic acid (TFA) etched latex glove surfaces allowed the direct determination (exact molecular weight) of Hevein, REF and a truncated form of REF (tREF) within nine different brands of natural latex gloves by means of MALDI-TOF-MS in the linear mode. MALDI mass spectrometry demonstrated that Hevein, tREF and REF were present on the inner surfaces (in direct contact with the skin) of many, but not all, investigated gloves without any prior extraction procedure. Additionally, different isoforms of the allergen Hevein were detected (exhibiting ragged C-termini). tREF and REF could always be detected beside each other, but were not observed on every latex glove sample, which contained Hevein. It was also demonstrated that there is a significant difference in terms of proteins and polymers between inner and outer surfaces of gloves, which helps to explain the different allergenic potential of these.MALDI imaging allowed for the first time the unambiguous localization of all three allergens in parallel and showed that Hevein was present on 36% of the investigated area of a latex glove with a certain localization, whereupon, tREF and REF were only found on 25% of the investigated material.     

Calcium-dependent secretion in human neutrophils: a proteomic approach

Bactericidal, proteolytic and signal proteins released by activated neutrophils play a major role in infection fighting and inflammatory processes. These proteins are mainly stored in organelles called granules until induction of their controlled exocytosis. The present work deals with the characterization of the proteins which are secreted upon activation of human neutrophils by ionomycin and calcium. Proteins were separated by two-dimensional gel electrophoresis and identified by peptide mass fingerprinting. Almost all the previously described soluble components of neutrophil granules could be identified. Moreover, several additional proteins were shown to be secreted by activated neutrophils, namely calgranulins, human cartilage glycoprotein of 39 kDa (HC gp-39), chitotriosidase, and annexin XI. Their subcellular localization and possible functions are discussed.     

Identification of proteins separated by one-dimensional sodium dodecyl sulfate/polyacrylamide gel electrophoresis with matrix-assisted laser desorption/ionization ion trap mass spectrometry; comparison with matrix-assisted laser desorption/ionization time-of-flight mass fingerprinting

Digests from ten gel bands containing low abundance proteins were analyzed by both matrix-assisted laser desorption/ionization ion trap (MALDI-IT) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) methods. MALDI-TOF techniques were able to identify only one protein from all 10 gel bands, while MALDI-IT identified eight proteins from the same 10 bands. The ability to perform MS/MS experiments with a MALDI-IT instrument leads to protein identifications based on both peptide molecular mass and sequence information, and is much less prone to errors and uncertainties introduced by peptide fingerprinting methodologies in which protein identification is based on peptide molecular masses alone.     

Double electrophoretic separation and lectin analyses of the component chains of secretory immunoglobulin A from human saliva

A new method is presented for the separation of secretory immunoglobulin A (SIgA) from salivary samples. Salivary proteins (from parotid or stimulated whole mouth saliva) were precipitated with methanol to concentrate SIgA from salivary samples whilst removing other salivary proteins. SIgA purified from breast milk and salivary proteins was separated by 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under nonreducing conditions. Following completion of electrophoresis the top strip of gel was removed and the proteins present reduced with dithiothreitol. The gel strip was then applied to the top of a second 10% SDS gel, and the proteins were electrophoresed and then stained by Coomassie Brilliant Blue R-250. Three major protein bands were stained in all samples corresponding in molecular mass to secretory component, alpha-heavy chain and light chains of SIgA. Separated proteins were also electroblotted onto nitrocellulose and stained by fluorescein isothiocyanate (FITC). Lectin analysis was then used to detect the O-glycans present on IgA1. Lectins from Helix aspersa and Arachis hypogaea were used to determine the amount of terminal N-acetyl galactosamine and nonsialylated O-glycans, respectively. Maclura pomifera lectin was used to determine the total amount of IgA1 present on the blots. The results indicate that SlgA in stimulated whole mouth saliva, stimulated parotid saliva and purified from breast milk contain similar O-glycans.     

Characterization of proteins in latex of the opium poppy (Papaver somniferum) using two-dimensional gel electrophoresis and microsequencing

The opium poppy (Papaver somniferum) belongs to the group of latex-containing plants. Latex is the milky-like fluid within laticifer cells. In this study, poppy latex was analyzed with respect to ultrastructure, alkaloid, and protein content. The main goal of this project was the examination of the proteins by two-dimensional gel electrophoresis. In a proteomics approach, we investigated two main fractions of the latex, namely the cytosolic serum and the sedimented fraction containing the alkaloid-accumulating vesicles. Of the serum, representing the protein-rich part of the latex, 75 spots were analyzed by internal peptide microsequencing, followed by a database searching. For 69 proteins a function could be assigned due to homology to known proteins, whereas six spots could not be identified. Furthermore, codeinone reductase, a representative of the specific enzyme system in morphine biosynthesis, could be detected within the cytosolic serum fraction. In the vesicle-containing pellet, 23 protein spots were analyzed. An attempt was also made to separate the vesicle pellet by density centrifugation, followed by investigation of the alkaloid content, ultrastructure, and protein pattern. This study describes the first database of soluble proteins present in the latex of P. somniferum     

Papain Purification Insights: Monitoring by Electrophoretic Approaches and MALDI-TOF Peptide Mass Fingerprint Analyses

Papain was purified from dried Carica papaya latex by fractioned salt precipitation in presence of sodium tetrathionate to preserve enzymatic activity. Purification was followed by different electrophoretic methods. Identification of the purified product was afforded by submitting the peptides obtained by tryptic digestion of papain to matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF/TOF MS) analysis. Comparison of the peptide masses analyzed by peptide mass fingerprinting (PMF) MALDI-TOF and those obtained by theoretical tryptic digestion, revealed the presence of some peptides belonging the other three endopeptidases contained in papaya latex (very similar to papain in molecular weight and pI) in the purified fraction of papain. The PMF by MALDI-TOF could be applied as a method to follow papain purification.     

Improvement of gel‐separated protein identification by DMF‐assisted digestion and peptide recovery after electroblotting

In‐gel digestion of gel‐separated proteins is a major route to assist in proteomics‐based biological discovery, which, however, is often embarrassed by its inherent limitations such as the low digestion efficiency and the low recovery of proteolytic peptides. For overcoming these limitations, many efforts have been directed at developing alternative methods to avoid the in‐digestion. Here, we present a new method for efficient protein digestion and tryptic peptide recovery, which involved electroblotting gel‐separated proteins onto a PVDF membrane, excising the PVDF bands containing protein of interest, and dissolving the bands with pure DMF (≥99.8%). Before tryptic digestion, NH₄HCO₃ buffer was added to moderately adjust the DMF concentration (to 40%) in order for trypsin to exert its activity. Experimental results using protein standards showed that, due to actions of DMF in dissolving PVDF membrane and the membrane‐bound substances, the proteins were virtually in‐solution digested in DMF‐containing buffer. This protocol allowed more efficient digestion and peptide recovery, thereby increasing the sequence coverage and the confidence of protein identification. The comparative study using rat hippocampal membrane‐enriched sample showed that the method was superior to the reported on‐membrane tryptic digestion for further protein identification, including low abundant and/or highly hydrophobic membrane proteins.     

Estimation of isoelectric points of human plasma proteins employing capillary isoelectric focusing and peptide isoelectric point markers

Synthetic UV-detectable peptide pI markers were used to estimate isoelectric point (pI) values of proteins separated by capillary isoelectric focusing (CIEF) followed by cathodic mobilization in the absence of denaturing agents. The pI calculation and quantitative analysis of purified proteins showed the feasibility of these peptides as pI markers and internal standards in CIEF separation of proteins. Estimation of pI values of major proteins in human plasma was performed using the peptide pI markers, and the values were compared with those previously obtained by gel isoelectric focusing (IEF). Sera of immunoglobulin G (IgG) myeloma patients, which showed characteristic peaks of myeloma IgG in their CIEF patterns, were also subjected to the analysis and the pI values of the myeloma proteins have been estimated.     

Characterization of native and recombinant peptidyl prolyl cis-trans isomerases derived from Methanococcus thermolithotrophicus based on cDNA sequence

It is important to establish whether a recombinant protein is an authentic copy of the predicted cDNA sequence. In this study, recombinant protein for native peptidyl prolyl cis-trans isomerase (N-PPIase) and double-labeled (13C- and 15N-) protein (DL-PPIase) appeared on the sodium dodecyl sulfate (SDS) electropherograms as two bands for N-PPIase and four bands for DL-PPIase. Since the N-terminal amino acid residues of all bands were the same, we characterized these bands using the peptide mapping method and amino acid composition analysis. Peptide mapping of the proteins seemed to be almost identical but they could not reflect the whole amino acid sequences of the protein. The bands on the polyvinylidene difluoride (PVDF) membrane, electroblotted after SDS-polyacrylamide gel electrophoresis (SDS-PAGE), were hydrolyzed and their amino acid composition was analyzed using a highly sensitive 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) amino acid analysis and compared with the cDNA sequences for proteins. The matching score (sigma(T%-E%)2) for similarity of proteins was calculated by summation of the square difference between the theoretical (T%) and the experimental (E%) amino acid composition of the recombinant protein. The amino acid composition of all bands of both proteins showed more than 93% of the theoretical values. The major molecular weights of both proteins were 16812 and 17694 by electrospray ionization (ESI)-mass spectrometry. However, the purified proteins also contained minor compounds with Mr of 3721 for N-PPIase and 5285 for DL-PPIase. These compounds were considered to be nonpeptidyl products that comigrated with the protein. Similarities of the amino acid composition of the four bands were more than 98%. Our results indicate that AQC amino acid analysis is the most suitable method for characterization of a recombinant protein.     

A two dimensional electrophoresis database of a human Jurkat T-cell line

About 2000 protein spots of human Jurkat T-cells were detected by high resolution two-dimensional gel electrophoresis (2-DE) and were characterized in terms of their isoelectric point and molecular mass. A 2-DE database was constructed and is available at http://www.mpiib-berlin.mpg.de/2D-PAGE/. At present the database contains 67 identified protein spots. These proteins were identified after tryptic digestion by peptide mass fingerprinting with delayed extraction-matrix assisted laser desorption/ionization-mass spectrometry (DE-MALDI-MS). Proteins with a sequence coverage of at least 30% were introduced in the database. This sequence coverage could not always be obtained by using only the matrix alpha-cyano-4-hydroxycinnamic acid (CHCA) for the mass analysis. Therefore, an additional mass spectrum was recorded by using 2,5-dihydroxybenzoic acid (DHB). Usually, additional mass peaks were detected and together with the mass spectrum of CHCA this resulted in the desired sequence coverage.     

Mass spectrometry of peptides and proteins using digestion by a grape cysteine protease at pH 3

Cysteine protease from grapevine (Vitis vinifera) belongs to those resistant proteins, which survive the process of vinification and can therefore be detected as wine components. Its amino acid sequence shows a homology to other members of the papain family, but the enzyme has only partially been explored so far. In order to get more biochemical information with the help of mass spectrometry (MS), wine proteins were collected by ultrafiltration and separated by gel permeation chromatography. The purified enzyme surprisingly displayed a high molecular mass value of around 200 kDa, indicating a possible oligomeric status and aggregation, as it entered only negligibly the separating 10% gel during polyacrylamide gel electrophoresis. The isoelectric point (pI) value of 3.6 was determined by chromatofocusing. Matrix‐assisted laser desorption/ionization (MALDI)‐MS was employed to evaluate the cleavage specificity and usefulness of the isolated cysteine protease in protein and peptide research. A potential applicability could be anticipated from the efficient digestion performance in volatile ammonium formate buffers at pH 3. Common peptides were digested and the resulting products analyzed by MS/MS sequencing. Then, mixtures of protein standards and extracted barley nuclear proteins were processed in the same way. Grape cysteine protease is nonspecific but shows a certain preference for Arg, Lys, and also Leu residues. Compared with papain, it seems not to require fully the presence of a large hydrophobic residue adjacent to that at the cleavage site. The enzyme is suitable for protein research as it produces peptides of a reasonable length in acidic pH.     

Rapid and sensitive separation of trace level protein digests using microfabricated devices coupled to a quadrupole--time-of-flight mass spectrometer

The application of microfabricated devices coupled to a quadrupole time-of-flight mass spectrometer (Qq-TOF-MS) is presented for the analysis of trace level digests of gel-isolated proteins. In order to enhance the sample loading for proteomics analyses, two different on-chip sample preconcentration techniques were evaluated. First, a sample stacking procedure that used polarity switching to remove the sample buffer prior to zone electrophoresis was easily integrated on the microfabricated devices. With the present chip design, this preconcentration technique provided up to 70 nL sample injection with sub-nM detection limits for most peptide standards. For applications requiring larger sample loading, a disposable adsorption preconcentrator using a C18 membrane is incorporated outside the chip. This preconcentration method yielded lower peptide recoveries than that obtainable with sample stacking, and provided a convenient means of injecting several microL of sample with detection limits of typically 2.5 nM for hydrophobic peptides. The analytical merits of both sample enrichment approaches are described for the identification of bands isolated from two-dimensional (2-D) gel separation of protein extracts from Haemophilus influenzae. Accurate molecular mass measurements (< 5 ppm) in peptide mapping experiments is obtained by introducing an internal standard via a post-separation channel. Rapid identification of trace level peptides is also demonstrated using on-line tandem mass spectrometry and database searching with peptide sequence tags.     

Quantification, 2DE analysis and identification of enriched glycosylated proteins from mouse muscles: Difficulties and alternatives

One of the problems with 2DE is that proteins present in low amounts in a sample are usually not detected, since their signals are masked by the predominant proteins. The elimination of these abundant proteins is not a guaranteed solution to achieve the desired results. The main objective of this study was the comparison of common and simple methodologies employed for 2DE analysis followed by MS identification, focusing on a pre‐purified sample using a wheat germ agglutinin (WGA) column. Adult male C57Black/Crj6 (C57BL/6) mice were chosen as the model animal in this study; the gastrocnemius muscles were collected and processed for the experiments. The initial fractionation with succinylated WGA was successful for the elimination of the most abundant proteins. Two quantification methods were employed for the purified samples, and bicinchoninic acid (BCA) was proven to be most reliable for the quantification of glycoproteins. The gel staining method, however, was found to be decisive for the detection of specific proteins, since their structures affect the interaction of the dye with the peptide backbone. The Coomassie Blue R‐250 dye very weakly stained the gel with the WGA purified sample. When the same gel was stained with silver nitrate, however, MS could positively assign 12 new spots. The structure of the referred proteins was not found to be prone to interaction with Coomassie blue.     

Changes in electrokinetic properties of natural rubber latex after surface chemical modifications

High-ammonia latex concentrate prepared from doubly-concentrifuged fieldHevea latex was exhaustively dialyzed to remove any residual water-soluble non-rubber constituents. The specially purified latex was then treated with specific chemical reagents to modify the surface ionogenic groupings originally present on the latex particle surface. The electrophoretic mobility of the modified latexes was investigated as a function of pH. The change in electrokinetic properties of the surface-modified latex was explained in terms of chemical modification to the ionogenic groups of the adsorbed layer of proteins and long chain fatty acid soaps on the latex particle surface, the negative charges of which are primarily responsible for the colloidal stability of the latex. For comparison direct extraction of the long-chain fatty acid soaps from the specially purified latex by solvent was also carried out. Present results indicate that the number of carboxyl groups from the adsorbed long-chain fatty acid soaps plays a major role in the stabilization of the latex concentrate. In comparison the contribution of negative charges from the adsorbed proteins towards the stability of the latex is of less importance.     

Properties of mouse vomeronasal receptor and assessment of its role in pheromone signalling

Vomeronasal type 2 receptor (V2Rx) from Swiss mouse (Mus musculus (L.)) was analyzed by high-resolution ion-exchange chromatography, reversed-phase high-performance liquid chromatography (RP-HPLC), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), Ion Spray tandem mass spectrometry (MS/MS), 10% sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and 1-aminoanthracene (1-AMA) fluorometric assay. Vomeronasal sensory neuronal cell bound proteins were resolved into major protein peaks. Several proteins were identified and subsequently purified as the V2Rx receptor on 10% SDS-PAGE with trace amounts of other protein bands. The molecular weight of the identified V2Rx was 109 kDa. MALDI-TOF and micro-sequencing experiments demonstrated that the identified V2Rx receptor shared considerable sequence similarity with vomeronasal receptor type 2 (NCBI Accession Number AB267725), which is a seven transmembrane peptide with 912 amino acid residues. The molecular characterization revealed that the N-terminus of the V2Rx receptor contained the 11GAEAAE16 domain involved in pheromone signalling. The biometric assay (octanamine-V2Rx binding) showed the identified V2Rx receptor and mouse sex pheromone to 2-octanamine (methyl heptyl) in a 1:1 ratio. Uptake of odourants determined in physiological condition showed enhanced V2Rx receptors as volatile hydrophobic pheromone receptors in the vomeronasal neuron of the Swiss mouse.     

Rapid analysis of a peptide by fast-atom bombardment mass spectrometry after polyacrylamide gel electrophoresis

Gel electrophoresis has been a powerful technique for the separation of peptides and proteins for many years. After electrophoresis separation on a polyacrylamide gel, the peptide bradykinin was localized using Coomassie Blue as a staining dye. Excess dye was removed by washing the gel with water. For mass spectrometric analysis, bands containing the peptide were crushed, extracted with acetic acid and the eluent applied to the fast-atom bombardment probe. Under these conditions the protonated molecule of bradykinin was clearly observed. Also apparent were sequence ions at about the same intensity observed from authentic bradykinin.     

Analysis of post-translational modification and characterization of the domain structure of dynamin A from Dictyostelium discoideum

The post-translational modifications of the 96 kDa protein dynamin A from Dictyostelium discoideum were analyzed using Q-TOF mass spectrometry. The accurate molecular mass of the intact protein revealed a covalent modification causing an additional mass of 42 Da. The modification could be identified as N-terminal acetylation by tandem mass spectrometry. Extracted ion chromatograms for the a(1) and b(1) ion of the tryptic T1 peptide were used to detect the acetylated peptide within 54 nanoelectrospray ionization tandem mass spectra. Owing to the accurate molecular mass of the intact protein, additional covalent modifications could be excluded. In addition to the covalent modification, the domain structure of dynamin A was determined by applying a combination of limited proteolysis, sodium dodecylsulfate polyacrylamide gel electrophoresis, automated tandem mass spectrometry and protein database searching.     

Identification of proteins from one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis using electrospray quadrupole-time-of-flight tandem mass spectrometry

The potential of electrospray tandem mass spectrometry using a quadrupole-time-of-flight tandem mass spectrometer was evaluated for the identification of two unknown proteins from one-dimensional polyacrylamide gel electrophoresis (1-D-PAGE). Two proteins from cellular cultures of mammary epithelia were purified by 1D-PAGE. Their identification was achieved using peptide sequence tags generated by LC/Q-TOF-MS/MS, whereas MALDI-TOF mass mapping failed for these proteins obtained from simple 1D-PAGE separation.     

Towards a human repertoire of monocytic lysosomal proteins

The lysosomal compartment of human monocytic cells has never been investigated by a proteomic approach. By a combination of one-dimensional (1-D) and two-dimensional (2-D) gel electrophoresis, protein identification by N-terminal sequencing, matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS) peptide mass fingerprinting and tandem mass spectrometry (MS/MS) peptide sequence analysis, we initiated an exhaustive study of the human lyososomal proteome, which aims at establishing a 2-D reference map of human soluble lyososomal proteins. Human monocytic U937 cells were induced to secrete lysosomal soluble hydrolases by addition of NH4Cl in the culture medium. Since lysosomal soluble proteins are characterized by the presence of mannose-6-phosphate, they were purified on an affinity support bearing mannose-6-phosphate receptor. Analysis of the purified fraction led to the preliminary identification of fifteen proteins, among which twelve are well-known lysosomal hydrolases, one is assumed to be lysosomal on the basis of sequence homology to cysteine proteinases of the papain family, and two (leukocystatin and the human cellular repressor of E1A-stimulated genes) are described here for the first time as mannose-6-phosphate-containing proteins.     

Novel procedure for the identification of proteins by mass fingerprinting combining two-dimensional electrophoresis with fluorescent SYPRO red staining

The fluorescent sensitive SYPRO Red dye was successfully employed to stain proteins in two-dimensional gels for protein identification by peptide mass fingerprinting. Proteins which are not chemically modified during the SYPRO Red staining process are well digested enzymatically in the gel and hence the resulting peptides can be efficiently eluted and analysed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). A SYPRO Red two-dimensional gel of a complex protein extract from Candida albicans was analysed by MALDI-TOF MS. The validity of SYPRO Red staining was demonstrated by identifying, via peptide mass fingerprinting, 10 different C. albicans proteins from a total of 31 selected protein spots. The peptide mass signal intensity, the number of matched peptides and the percentage of coverage of protein sequences from SYPRO Red-stained proteins were similar to or greater than those obtained in parallel with the modified silver protein gel staining. This work demonstrates that fluorescent SYPRO Red staining is compatible with the identification of proteins separated on polyacrylamide gel and that it can be used as an alternative to silver staining. As far as we know, this is the first report in which C. albicans proteins separated using 2-D gels have been identified by peptide mass fingerprinting. The improved technique described here should be very useful for carrying out proteomic studies.