Improved identification of wheat gluten proteins through alkylation of cysteine residues and peptide-based mass spectrometry

Characterization among and within Sicilian Tetraploid Wheat Landraces by Gluten Protein Analysis for Traceability Purposes

The criteria of "Distinctness, Uniformity and Stability" as well as a high "overall quality index" are used to register the Italian modern varieties to the national register. Differently, local conservation varieties can be certified under different EU Directives that facilitate, as an overall objective, the preservation of biodiversity and the containment of genetic erosion. In recent years, products derived from ancient grains are perceived to be healthier and more sustainable by consumers, especially in Italy, with consequent higher market prices. The ancient tetraploid wheat varieties registered in the national register of conservation varieties amount to 28, 24 of which are Sicilian. They are supposed to have wide genetic variability compared to modern ones, making them vulnerable to fraud because they are difficult to trace. It is therefore important to have tools able to discriminate between autochthonous Sicilian varieties. This can be completed by gluten proteins composition, which also provides information on the technological properties of derived products. Fifty-one accessions belonging to twenty-two ancient varieties of Sicilian tetraploid (mostly durum) wheat were analyzed. Although wide intra-accession and intra-varietal variability measurements were assessed, the gliadin pattern of bulks of seeds belonging to each variety was discriminatory. Moreover, differences in technological attitudes were found between landraces. This paves the way to use gluten protein patterns for traceability, allowing local farmers and producers to valorize their products and assure consumers regarding the transparency of the entire supply chain.

A systematic review on the recent advances of wheat allergen detection by mass spectrometry: future prospects

Wheat is one of the three major staple foods in the world. Although wheat is highly nutritional, it has a variety of allergenic components that are potentially fatal to humans and pose a significant hazard to the growth and consumption of wheat. Wheat allergy is a serious health problem, which is becoming more and more prevalent all over the world. To address and prevent related health risks, it is crucial to establish precise and sensitive detection and analytical methods as well as an understanding of the structure and sensitization mechanism of wheat allergens. Among various analytical tools, mass spectrometry (MS) is known to have high specificity and sensitivity. It is a promising non immune method to evaluate and quantify wheat allergens. In this article, the current research on the detection of wheat allergens based on mass spectrometry is reviewed. This review provides guidance for the further research on wheat allergen detection using mass spectrometry, and speeds up the development of wheat allergen research in China.

Proteomic Characterization of Wheat Protein Fractions Taken at Different Baking Conditions

Food processing conditions affect the structure, solubility, and therefore accurate detection of gluten proteins. We investigated the influence of dough, bread, and pretzel making on the composition of different wheat protein fractions obtained by Osborne fractionation. The albumin/globulin, gliadin, and glutenin fractions from flour, dough, crispbread, bread, and pretzel were analyzed using RP-HPLC, SDS-PAGE, and untargeted nanoLC-MS/MS. This approach enabled an in-depth profiling of the fractionated proteomes and related compositional changes to processing conditions (mixing, heat, and alkali treatment). Overall, heat treatment demonstrated the most pronounced effect. Label-free quantitation revealed significant changes in the relative abundances of 82 proteins within the fractions of bread crumb and crust in comparison to flour. Certain gluten proteins showed shifts or reductions in particular fractions, indicating their incorporation into the gluten network through SS and non-SS cross-links. Other gluten proteins were enriched, suggesting their limited involvement in the gluten network formation.

Challenges and opportunities for proteomics and the improvement of bread wheat quality

Wheat remains a critical global food source, pressured by climate change and the need to maximize yield, improve processing and nutritional quality and ensure safety. An enormous amount of research has been conducted to understand gluten protein composition and structure in relation to end-use quality, yet progress has become stagnant. This is mainly due to the need and inability to biochemically characterize the intact functional glutenin polymer in order to correlate to quality, necessitating reduction to monomeric subunits and a loss of contextual information. While some individual gluten proteins might have a positive or negative influence on gluten quality, it is the sum total of these proteins, their relative and absolute expression, their sub-cellular trafficking, the amount and size of glutenin polymers, and ratios between gluten protein classes that define viscoelasticity of gluten. The sub-cellular trafficking of gluten proteins during seed maturation is still not completely clear and there is evidence of dual pathways and therefore different destinations for proteins, either constitutively or temporally. The trafficking of proteins is also unclear in endosperm cells as they undergo programmed cell death; Golgi disappear around 12 DPA but protein filling continues at least to 25 DPA. Modulation of the timing of cellular events will invariably affect protein deposition and therefore gluten strength and function. Existing and emerging proteomics technologies such as proteoform profiling and top-down proteomics offer new tools to study gluten protein composition as a whole system and identify compositional patterns that can modify gluten structure with improved functionality.

Post-translational modifications and glycoprofiling of palivizumab by UHPLC–RPLC/HILIC and mass spectrometry

Viral infections are progressively becoming a global health burden, as witnessed in the ongoing COVID-19 pandemic. Respiratory Syncytial Virus (RSV) is another highly contagious negative-sense RNA virus that causes lower respiratory tract infections and high mortality in infants. Palivizumab (Synagis^®) is the only humanized monoclonal antibody (mAb) approved by the FDA against RSV. The virus neutralization efficacy often depends on the nature and abundance of the glycoforms in therapeutic mAbs. Therefore, a thorough estimation of their PTM profile, especially glycosylation, is relevant. Here, we describe the intact and released glycan analysis of palivizumab (Synagis^®) using HILIC chromatography and mass spectrometry. We detected five glycoforms (Man5/G0FB, G0F/G1F, G1F/G1F, G0FB/G0FB, and G2F/G2F) in deconvoluted MS spectra of intact glycosylated palivizumab. The mapping of the peptide and glycopeptides using LC–ESI–MS led to the detection of associated PTMs and the direct identification of a glycopeptide, GlcNAc₃Man₂. EEQYNSTYR, derived from the heavy chain of palivizumab.Release glycan analysis using UHPLC–HILIC revealed a typical glycan profile consisting of major glycans, G0F (33.94%), G1F (35.50%), G2F (17.24%) also reported previously and minor G1F’ (5.81%), Man5 (3.96%) and G0FB (2.26%) forms with the superior resolution of isomeric G1F/G1F’. Next, we provide the first experimental evidence of Neu5Gc in the commercial palivizumab formulation using DMB labelling. The estimated monosaccharide composition was consistent with previous studies. The findings of the study highlight the efficiency of the release glycan method in providing a correct measure of the total palivizumab glycan pool compared to the intact glycoprotein/glycopeptide approach. The UHPLC–RPLC/HILIC and MS combinations provide a more comprehensive glycoprofile assessment due to the parallel use of fluorescent labels for the analysis of the release of N-glycan, sialic acid, and monosaccharide composition. This approach is suitable for quick quality testing and market surveillance of therapeutic mAbs. Alongside a well-perceived need for cost-effective immunoprophylaxis and the ongoing fast-paced development of next-generation variants of palivizumab, such as MEDI8897, the study reiterates glycosylation as a critical parameter that needs monitoring for drug characterization and quality control.

Post translational modifications of milk proteins in geographically diverse goat breeds

Goat milk is a source of nutrition in difficult areas and has lesser allerginicity than cow milk. It is leading in the area for nutraceutical formulation and drug development using goat mammary gland as a bioreactor. Post translational modifications of a protein regulate protein function, biological activity, stabilization and interactions. The protein variants of goat milk from 10 breeds were studied for the post translational modifications by combining highly sensitive 2DE and Q-Exactive LC-MS/MS. Here we observed high levels of post translational modifications in 201 peptides of 120 goat milk proteins. The phosphosites observed for CSN2, CSN1S1, CSN1S2, CSN3 were 11P, 13P, 17P and 6P, respectively in 105 casein phosphopeptides. Whey proteins BLG and LALBA showed 19 and 4 phosphosites respectively. Post translational modification was observed in 45 low abundant non-casein milk proteins mainly associated with signal transduction, immune system, developmental biology and metabolism pathways. P_asp is reported for the first time in 47 sites. The rare conserved peptide sequence of (SSSEE) was observed in αS1 and αS2 casein. The functional roles of identified phosphopeptides included anti-microbial, DPP-IV inhibitory, anti-inflammatory and ACE inhibitory. This is first report from tropics, investigating post translational modifications in casein and non-casein goat milk proteins and studies their interactions.

Comprehensive Comparison of Clinically Relevant Grain Proteins in Modern and Traditional Bread Wheat Cultivars

Bread wheat (Triticum aestivum L.) is one of the most valuable cereal crops for human consumption. Its grain storage proteins define bread quality, though they may cause food intolerances or allergies in susceptible individuals. Herein, we discovered a diversity of grain proteins in three Ukrainian wheat cultivars: Sotnytsia, Panna (both modern selection), and Ukrainka (landrace). Firstly, proteins were isolated with a detergent-containing buffer that allowed extraction of various groups of storage proteins (glutenins, gliadins, globulins, and albumins); secondly, the proteome was profiled by the two-dimensional gel electrophoresis. Using multi-enzymatic digestion, we identified 49 differentially accumulated proteins. Parallel ultrahigh-performance liquid chromatography separation followed by direct mass spectrometry quantification complemented the results. Principal component analysis confirmed that differences among genotypes were a major source of variation. Non-gluten fraction better discriminated bread wheat cultivars. Various accumulation of clinically relevant plant proteins highlighted one of the modern genotypes as a promising donor for the breeding of hypoallergenic cereals.

Wheat Gluten Amino Acid Analysis by High-Performance Anion-Exchange Chromatography with Integrated Pulsed Amperometric Detection

The present chapter describes an accurate and user-friendly method for determining amino acid composition of wheat gluten proteins and their gliadin and glutenin fractions. The method consists of hydrolysis of the peptide bonds in 6.0 M hydrochloric acid (HCl) solution at 110 °C for 24 h, followed by evaporation of the acid and separation of the free amino acids by high-performance anion-exchange chromatography with integrated pulsed amperometric detection (HPAEC-IPAD). In contrast to conventional methods, the analysis requires neither pre- or post-column derivatization nor a time-consuming oxidation or derivatization step prior to hydrolysis. Correction factors account for incomplete release of Val and Ile even after hydrolysis for 24 h and for losses of Ser during evaporation. Gradient conditions including an extra eluent allow multiple sequential sample analyses without risk of Glu accumulation on the anion-exchange column which otherwise would result from high Gln levels in gluten proteins.

Targeted LC-MS/MS Reveals Similar Contents of α-Amylase/Trypsin-Inhibitors as Putative Triggers of Nonceliac Gluten Sensitivity in All Wheat Species except Einkorn

Amylase/trypsin-inhibitors (ATIs) are putative triggers of nonceliac gluten sensitivity, but contents of ATIs in different wheat species were not available. Therefore, the predominant ATIs 0.19 + 0.53, 0.28, CM2, CM3, and CM16 in eight cultivars each of common wheat, durum wheat, spelt, emmer, and einkorn grown under the same environmental conditions were quantitated by targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) and stable isotope dilution assays using specific marker peptides as internal standards. The results were compared to a label-free untargeted LC-MS/MS analysis, in which protein concentrations were determined by intensity based absolute quantitation. Both approaches yielded similar results. Spelt and emmer had higher ATI contents than common wheat, with durum wheat in between. Only three of eight einkorn cultivars contained ATIs in very low concentrations. The distribution of ATI types was characteristic for hexaploid, tetraploid, and diploid wheat species and suitable as species-specific fingerprint. The results point to a better tolerability of einkorn for NCGS patients, because of very low total ATI contents.

Membrane Proteomics in Gram-Positive Bacteria: Two Complementary Approaches to Target the Hydrophobic Species of Proteins

This protocol represents a detailed instruction how to prepare protein samples in order to raise mass spectrometry-based identification and quantification rates with respect to the challenging class of membrane proteins. This will increase comprehensiveness of global proteome studies on the one hand but could also be of interest for researchers targeting specific membrane proteins or membrane protein sequences on the other hand. The protocol is a composite of two parts, one focusing on the identification of protein sequences exterior to a cellular membrane (loops of integral membrane proteins, peripheral membrane proteins), and the other part targeting primarily protein domains spanning the lipid bilayer. The feasibility of the protocol, as it is described here, was originally shown for the gram-positive pathogenic bacterium Staphylococcus aureus but should be applicable to any kind of membrane protein.

Food for thought: Selecting the right enzyme for the digestion of gluten

Gluten describes a complex mixture of proteins found in wheat, rye, barley and oats that pose a health risk to people affected by conditions such as coeliac disease and non-coeliac gluten sensitivity. Complete digestion of gluten proteins is of critical importance during quantitative analysis. To this end, chymotrypsin was investigated for its ability to efficiently and reproducibly digest specific classes of gluten in barley. Using proteomics a chymotryptic peptide marker panel was elucidated and subjected to relative quantification using LC-MRM-MS. Thorough investigation of peptide markers revealed robust and reproducible quantification with CVs <15% was possible, however a greater proportion of non-specific cleavage variants were observed relative to trypsin. The selected peptide markers were assessed to ensure their efficient liberation from their parent proteins. While trypsin remains the preferred enzyme for quantification of the avenin-like A proteins, the B-, D- and γ-hordeins, chymotrypsin was the enzyme of choice for the C-hordeins.

Quantitation of the immunodominant 33-mer peptide from α-gliadin in wheat flours by liquid chromatography tandem mass spectrometry

Coeliac disease (CD) is triggered by the ingestion of gluten proteins from wheat, rye, and barley. The 33-mer peptide from α2-gliadin has frequently been described as the most important CD-immunogenic sequence within gluten. However, from more than 890 published amino acid sequences of α-gliadins, only 19 sequences contain the 33-mer. In order to make a precise assessment of the importance of the 33-mer, it is necessary to elucidate which wheat species and cultivars contain the peptide and at which concentrations. This paper presents the development of a stable isotope dilution assay followed by liquid chromatography tandem mass spectrometry to quantitate the 33-mer in flours of 23 hexaploid modern and 15 old common (bread) wheat as well as two spelt cultivars. All flours contained the 33-mer peptide at levels ranging from 91–603 μg/g flour. In contrast, the 33-mer was absent (<limit of detection) from tetra- and diploid species (durum wheat, emmer, einkorn), most likely because of the absence of the D-genome, which encodes α2-gliadins. Due to the presence of the 33-mer in all common wheat and spelt flours analysed here, the special focus in the literature on this most immunodominant peptide seems to be justified.

Isolation and characterization of gluten protein types from wheat, rye, barley and oats for use as reference materials

Gluten proteins from wheat, rye, barley and, in rare cases, oats, are responsible for triggering hypersensitivity reactions such as celiac disease, non-celiac gluten sensitivity and wheat allergy. Well-defined reference materials (RM) are essential for clinical studies, diagnostics, elucidation of disease mechanisms and food analyses to ensure the safety of gluten-free foods. Various RM are currently used, but a thorough characterization of the gluten source, content and composition is often missing. However, this characterization is essential due to the complexity and heterogeneity of gluten to avoid ambiguous results caused by differences in the RM used. A comprehensive strategy to isolate gluten protein fractions and gluten protein types (GPT) from wheat, rye, barley and oat flours was developed to obtain well-defined RM for clinical assays and gluten-free compliance testing. All isolated GPT (ω5-gliadins, ω1,2-gliadins, α-gliadins, γ-gliadins and high- and low-molecular-weight glutenin subunits from wheat, ω-secalins, γ-75k-secalins, γ-40k-secalins and high-molecular-weight secalins from rye, C-hordeins, γ-hordeins, B-hordeins and D-hordeins from barley and avenins from oats) were fully characterized using analytical reversed-phase high-performance liquid chromatography (RP-HPLC), sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), N-terminal sequencing, electrospray-ionization quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF-MS) and untargeted LC-MS/MS of chymotryptic hydrolyzates of the single GPT. Taken together, the analytical methods confirmed that all GPT were reproducibly isolated in high purity from the flours and were suitable to be used as RM, e.g., for calibration of LC-MS/MS methods or enzyme-linked immunosorbent assays (ELISAs).

Improved Quantitation of Gluten in Wheat Starch for Celiac Disease Patients by Gel-Permeation High-Performance Liquid Chromatography with Fluorescence Detection (GP-HPLC-FLD)

Purified wheat starch (WSt) is commonly used in gluten-free products for celiac disease (CD) patients. It is mostly well-tolerated, but doubts about its safety for CD patients persist. One reason may be that most ELISA kits primarily recognize the alcohol-soluble gliadin fraction of gluten, but insufficiently target the alcohol-insoluble glutenin fraction. To address this problem, a new sensitive method based on the sequential extraction of gliadins, glutenins, and gluten from WSt followed by gel-permeation high-performance liquid chromatography with fluorescence detection (GP-HPLC-FLD) was developed. It revealed that considerable amounts of glutenins were present in most WSt. The gluten contents quantitated by GP-HPLC-FLD as sum of gliadins and glutenins were higher than those by R5 ELISA (gluten as gliadin content multiplied by a factor of 2) in 19 out of 26 WSt. Despite its limited selectivity, GP-HPLC-FLD may be applied as confirmatory method to ELISA to quantitate gluten in WSt.

Comparing Multiple Reaction Monitoring and Sequential Window Acquisition of All Theoretical Mass Spectra for the Relative Quantification of Barley Gluten in Selectively Bred Barley Lines

Celiac disease (CD) is a disease of the small intestine that occurs in genetically susceptible subjects triggered by the ingestion of cereal gluten proteins for which the only treatment is strict adherence to a life-long gluten-free diet. Barley contains four gluten protein families, and the existence of barley genotypes that do not accumulate the B-, C-, and D-hordeins paved the way for the development of an ultralow gluten phenotype. Using conventional breeding strategies, three null mutations behaving as recessive alleles were combined to create a hordein triple-null barley variety. Proteomics has become an invaluable tool for characterization and quantification of the protein complement of cereal grains. In this study multiple reaction monitoring (MRM) mass spectrometry, viewed as the gold standard for peptide quantification, was compared to the data-independent acquisition strategy known as SWATH-MS (sequential window acquisition of all theoretical mass spectra). SWATH-MS was comparable (p < 0.001) to MRM-MS for 32/33 peptides assessed across the four families of hordeins (gluten) in eight barley lines. The results of SWATH-MS analysis further confirmed the absence of the B-, C-, and D-hordeins in the triple-null barley line and showed significantly reduced levels ranging from <1% to 16% relative to wild-type (WT) cv Sloop for the minor γ-hordein class. SWATH-MS represents a valuable tool for quantitative proteomics based on its ability to generate reproducible data comparable with MRM-MS, but has the added benefits of allowing reinterrogation of data to improve analytical performance, ask new questions, and in this case perform quantification of trypsin-resistant proteins (C-hordeins) through analysis of their semi- or nontryptic fragments.

Identification of barley-specific peptide markers that persist in processed foods and are capable of detecting barley contamination by LC-MS/MS

Consumers, especially those with allergies and/or intolerances, should have confidence in two critical areas of food safety: foods should be correctly labelled and free from contamination. To this end, global proteomic analysis employing LC-MS/MS of gluten-enriched extracts derived from 12 barley cultivars was undertaken, providing a foundation for the development of MS-based quantitative methodologies that would enable the detection of barley contamination in foods. Subsequently, a number of candidate barley-specific peptide markers were evaluated by multiple-reaction monitoring MS. From an initial panel of 26, 9 peptide markers were unique to barley, yet present in a wide range of barley varieties. The analytical method was then used to examine a range of breakfast cereals and was able to detect barley in a barley-based breakfast cereal and a muesli, but additionally allowed detection of contamination of cereals that were comprised of ancient grains and in commercially-sourced flours, including amaranth, chia, buckwheat, millet, rice, corn, oats, rye, spelt and green wheat (0.01-0.08%). LC-MS/MS provides an alternative to ELISA approaches to monitor food safety and the identification of robust and sensitive cereal-specific peptide markers is the first step toward the adoption of this technology.

SIGNIFICANCE

Coeliac disease is a serious health issue affecting up to 70million people globally for which there is no cure. The only treatment is a life-long gluten-free diet. Contamination of foods can occur at many stages of food production from farm to fork. As such, accurate quantification and identification of the source (i.e. cereal) and type (e.g. gluten) of contamination is critical to the health and well-being of a subset of the population, including those affected by coeliac disease and non-coeliac gluten sensitivity.

Defining the wheat gluten peptide fingerprint via a discovery and targeted proteomics approach

Accurate, reliable and sensitive detection methods for gluten are required to support current EU regulations. The enforcement of legislative levels requires that measurement results are comparable over time and between methods. This is not a trivial task for gluten which comprises a large number of protein targets. This paper describes a strategy for defining a set of specific analytical targets for wheat gluten. A comprehensive proteomic approach was applied by fractionating wheat gluten using RP-HPLC (reversed phase high performance liquid chromatography) followed by a multi-enzymatic digestion (LysC, trypsin and chymotrypsin) with subsequent mass spectrometric analysis. This approach identified 434 peptide sequences from gluten. Peptides were grouped based on two criteria: unique to a single gluten protein sequence; contained known immunogenic and toxic sequences in the context of coeliac disease. An LC-MS/MS method based on selected reaction monitoring (SRM) was developed on a triple quadrupole mass spectrometer for the specific detection of the target peptides. The SRM based screening approach was applied to gluten containing cereals (wheat, rye, barley and oats) and non-gluten containing flours (corn, soy and rice). A unique set of wheat gluten marker peptides were identified and are proposed as wheat specific markers.

SIGNIFICANCE

The measurement of gluten in processed food products in support of regulatory limits is performed routinely. Mass spectrometry is emerging as a viable alternative to ELISA based methods. Here we outline a set of peptide markers that are representative of gluten and consider the end user's needs in protecting those with coeliac disease. The approach taken has been applied to wheat but can be easily extended to include other species potentially enabling the MS quantification of different gluten containing species from the identified markers.

High-Efficiency Recognition and Identification of Disulfide Bonded Peptides in Rat Neuropeptidome Using Targeted Electron Transfer Dissociation Tandem Mass Spectrometry

The main goal of the present study is to develop a method to recognize and identify endogenous intrachain disulfide bonded peptide, which are rarely sequenced in current peptidomics studies. In order to achieve highly efficient detection of these peptides in a neuropeptidome analysis, we alkylated the peptides, mined the raw mass spectrometry data, and then recognized the candidates of untreated disulfide bonded peptides from unalkylated peptide extracts. After removing more than 90% features, targeted electron transfer dissociation fragmentation was performed for detecting and fragmenting disulfide bonded peptides, and even most of them were present in low abundance in the original sample. Diverse endogenous disulfide bonded peptides were then detected and sequenced, opening up new perspectives for comprehensively understanding the response of a neuropeptidome.

ProPepper: a curated database for identification and analysis of peptide and immune-responsive epitope composition of cereal grain protein families

ProPepper is a database that contains prolamin proteins identified from true grasses (Poaceae), their peptides obtained with single- and multi-enzyme in silico digestions as well as linear T- and B-cell-specific epitopes that are responsible for wheat-related food disorders. The integrated database and analysis platform contains datasets that are collected from multiple public databases (UniprotKB, IEDB, NCBI GenBank), manually curated and annotated, and interpreted in three main data tables: Protein-, Peptide- and Epitope list views that are cross-connected by unique identifications. Altogether 21 genera and 80 different species are represented. Currently, the database contains 2146 unique and complete protein sequences related to 2618 GenBank entries and 35 657 unique peptide sequences that are a result of 575 110 unique digestion events obtained by in silico digestion methods involving six proteolytic enzymes and their combinations. The interface allows advanced global and parametric search functions along with a download option, with direct connections to the relevant public databases.

Database URL:https://propepper.net

Analytical platforms in vitreoretinal proteomics

Current proteomic technologies can effectively be used to study the proteins of the vitreous body and retina in health and disease. The use of appropriate samples, analytical platform and bioinformatic method are essential factors to consider when undertaking such studies. Certain proteins may hinder the detection and evaluation of more relevant proteins associated with pathological processes if not carefully considered, particularly in the sample preparation and data analysis stages. The utilization of more than one quantification technique and database search program to expand the level of proteome coverage and analysis will help to generate more robust and worthwhile results. This review discusses important aspects of sample processing and the use of label and label-free quantitative proteomics strategies applied to the vitreous and retina.

Formation and reshuffling of disulfide bonds in bovine serum albumin demonstrated using tandem mass spectrometry with collision-induced and electron-transfer dissociation

Thermolysin hydrolyzates of freshly isolated, extensively stored (6 years, 6 °C, dry) and heated (60 min, 90 °C, in excess water) bovine serum albumin (BSA) samples were analyzed with liquid chromatography (LC) electrospray ionization (ESI) tandem mass spectrometry (MS/MS) using alternating electron-transfer dissociation (ETD) and collision-induced dissociation (CID). The positions of disulfide bonds and free thiol groups in the different samples were compared to those deduced from the crystal structure of native BSA. Results revealed non-enzymatic posttranslational modifications of cysteine during isolation, extensive dry storage, and heating. Heat-induced extractability loss of BSA was linked to the impact of protein unfolding on the involvement of specific cysteine residues in intermolecular and intramolecular thiol-disulfide interchange and thiol oxidation reactions. The here developed approach holds promise for exploring disulfide bond formation and reshuffling in various proteins under conditions relevant for chemical, biochemical, pharmaceutical and food processing.

Intrinsic Size Parameters for Palmitoylated and Carboxyamidomethylated Peptides

Cross sections for 61 palmitoylated peptides and 73 cysteine-unmodified peptides are determined and used together with a previously obtained tryptic peptide library to derive a set of intrinsic size parameters (ISPs) for the palmitoyl (Pal) group (1.26 ± 0.04), carboxyamidomethyl (Am) group (0.92 ± 0.04), and the 20 amino acid residues to assess the influence of Pal- and Am-modification on cysteine and other amino acid residues. These values highlight the influence of the intrinsic hydrophobic and hydrophilic nature of these modifications on the overall cross sections. As a part of this analysis, we find that ISPs derived from a database of a modifier on one amino acid residue (Cys^Pal) can be applied on the same modification group on different amino acid residues (Ser^Pal and Tyr^Pal). Using these ISP values, we are able to calculate peptide cross sections to within ± 2% of experimental values for 83% of Pal-modified peptide ions and 63% of Am-modified peptide ions. We propose that modification groups should be treated as individual contribution factors, instead of treating the combination of the particular group and the amino acid residue they are on as a whole when considering their effects on the peptide ion mobility features.

Analysis of wheat prolamins, the causative agents of celiac sprue, using reversed phase high performance liquid chromatography (RP-HPLC) and matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS)

Wheat prolamins, commonly known as "gluten", are a complex mixture of 71-78 proteins, which constitute ~80% of the proteins in the wheat grains and supply 50% of the global dietary protein demand. Prolamins are also responsible for numerous gluten-induced disorders and determine the unique visco-elastic properties of the wheat dough. These properties necessitate the reliable determination of the prolamin composition in wheat grains and their derived products. Therefore, this study examined the impact of HPLC conditions, including column type, column temperature, flow rate, and the gradient of polar and non-polar solvents in the mobile phase, to improve the analytical resolution of prolamins. The following conditions were found optimal for analyses: column temperature 60 °C, flow rate 1.0 mL/min and an elution gradient of 20%-60% of 0.1% trifluoroacetic acid + acetonitrile in 60 min. For further improvement of resolution, gliadin and glutenin extracts were analyzed using MALDI-TOF-MS in combination with HPLC fractionation. Two semi-quantitative methods, densitometry of stained polyacrylamide gels and HPLC, were used to determine relative prolamin quantities and the correspondence between the methods was established. The combinatorial gluten analyses approach developed during the present study was used to analyze prolamin profiles of wheat transformants expressing DEMETER silencing artificial microRNA, and the results are discussed.

Improved glycation after ultrasonic pretreatment revealed by high-performance liquid chromatography-linear ion trap/Orbitrap high-resolution mass spectrometry

The glycation extent of bovine serum albumin (BSA) before and after ultrasonication was evaluated by MALDI-TOF and Orbitrap mass spectrometry. Ultrasonic pretreatment significantly improved the incorporation of galactose to BSA. Prior to ultrasonic pretreatment, only 12 sites (11 lysines and 1 arginine) were glycated, whereas the number of glycation sites was increased to 42, including 39 lysines and 3 arginines, after treatment. Average degree of substitution per peptide molecule of BSA (DSP) was used to evaluate the glycation level for each glycation site. The ultrasonic pretreatment significantly improved the DSP value of all glycation sites. The prevalently promoted glycation by ultrasonic pretreatment suggests that ultrasonication improves glycation through altering the structure of BSA throughout all three domains. An ultrahigh-resolution linear ion trap Orbitrap mass spectrometer facilitates unambiguous localization of glycation sites, allowing an in-depth analysis of the nature and extent of protein glycation at the molecular level. High-intensity ultrasonication can greatly improve protein glycation and, therefore, opens new routes to modify the functionality of proteins in a positive way.

Gluten Detection and Speciation by Liquid Chromatography Mass Spectrometry (LC-MS/MS)

Liquid chromatography tandem mass spectrometry (LC-MS/MS) has been used historically in proteomics research for over 20 years. However, until recently LC-MS/MS has only been routinely used in food testing for small molecule contaminant detection, for example pesticide and veterinary residue detection, and not as a replacement of microbiological food testing methods, specifically allergen analysis. Over the last couple of years, articles have started to be published which describe the detection of allergens by LC-MS/MS. In this article we will describe how LC-MS/MS can be applied in the area of gluten detection and how it can be used to specifically differentiate the species of gluten used in food, where specific markers for each variety of gluten can be simultaneously acquired and detected at the same time. The article will discuss the effect of variety on the peptide response observed from different wheat grain varieties and will describe the sample preparation protocol which is essential for generating the peptide markers used for speciation.