Search

The protein and peptide fraction of human milk samples collected from mothers of pre- and full-term infants in the first week after parturition was analysed by use of liquid chromatography-mass spectrometry and tandem mass spectrometry. By characterising the peptide sequence, we defined the pathway of casein hydrolysis which leads to the formation of small peptides through intermediate oligopeptides. It was found that the action of a plasmin-like enzyme acting on specific lysine residues is the primary step in casein degradation. This is followed by endopeptidases and/or exopeptidases mediated cleavage of the oligopeptides which, in turn, produces a multiplicity of short peptides differing by one or more amino acid residues. In this process, a series of potentially bioactive peptides (opioid, phosphopeptides) and their precursors are produced.

Donkey's milk (DM) has been extensively investigated as a valuable substitute of breast milk, often suitable to manage cow's milk protein allergy in infants. DM exhibits potent inhibitory properties against numerous microbial species. Although oligosaccharides and lipids might contribute to the antimicrobial potential, the current inventory of proteins is not able to justify the low count of microorganisms generally observed in DM. The shotgun proteomic analysis of fractionated DM disclosed a set of 94 gene products, 41% of which have documented antimicrobial activity or are involved in transferring the passive immunity to the donkey offspring. The concerted action of lysozyme, lactoferrin, immunoglobulins provides the molecular basis for part of the DM antibacterial potential. The pH -4.6 insoluble fraction contained significant levels of L-amino acid oxidase, identified with 11 unique peptides matching the horse homologue gene product. This enzyme catalyses the oxidative deamination of amino acids into ketoacids, producing ammonia and H2O2. κ-casein, likely occurring as a fully O-glycosylated protein, may concur to inhibit the adhesion of pathogenic microorganisms, along with other glycoproteins. Proteomics supports the alimentary use of DM not only as a substitute of human milk in early infancy, but also for growing children, convalescent, elderly people and general population. Significance Donkey's milk (DM) is acquiring increasing popularity because it is a suitable substitute of the human milk, when breastfeeding is not possible and infants suffer from cow's milk allergy. DM is characterized by a much lower microbial load compared to ruminants' milk. This feature has been traditionally attributed to the high content of lysozyme. DM exhibits potent activity against a broad range of bacteria, viruses and fungi, suggesting that other protein components can be responsible of the antimicrobial potential. The gel-free proteomic analysis of pH 4.6-insoluble and soluble (whey) fractions demonstrated that DM contains a large number of gene products involved in antimicrobial mechanisms and in transferring passive immunity to the donkey offspring. DM contains relatively high levels of L-amino acid oxidase that catalyses the oxidative deamination of amino acid substrates into ketoacids, with production of ammonia and H2O2. In combination with lysozyme, lactoferrin and immunoglobulins, the presence of L-amino acid oxidase provides the molecular basis of the antibacterial potential observed for DM. Considered the low microbial load, DM can be sanitated at mild conditions, thereby preserving many of the native nutritional traits. Thus, DM can be considered a safe and nutritionally valid alimentary resource for growing children, convalescent, elderly people and general population. Data of this study represent the largest inventory of proteins identified in Equidae milk, so far.

The intestine presides over a series of vital functions in the human body, among which the digestion/absorption of nutrients. Despite their major digestion role, the impact of the enzymes of the luminal intestinal surface on food components has been considered in relatively few experiments of simulated gastrointestinal digestion. In contrast, the identification of proteolitically stable peptides which survived digestion in multiphasal models that also included a step with small intestinal brush border membrane (BBM) peptidases has provided physiologically consistent results. Herein, we critically review the use of BBM enzymes to simulate the intestinal digestion of dietary polypeptides. Addressing the controversial issue of the in vitro-in vivo correspondence of the digestion models, the review emphasizes the need to establish consensus protocols to simulate the intestinal step, for instance using the BBM hydrolases at least in a selected number of cases. The factors that have limited the development of relevant models of intestinal degradationare discussed together with hints to possible alternatives, forthcoming approaches and future perspectives to reproduce the physiopathology of the human small intestine. (C) 2015 Elsevier Ltd. All rights reserved.

The lipid fraction of durum wheat (Triticum turgidum ssp. durum (Desf.) Husn.), cultivar Svevo, was characterized during grain maturation. Growing grain kernels were harvested at five key stages of development between 5 and 30 days post anthesis (dpa). Lipid evolution was assessed during kernel filling by gas chromatography-mass spectrometry (GC-MS) analysis of triacylglycerols and methylated free fatty acids (FFA) as well as by ultra-high performance liquid chromatography coupled to high resolution electrospray ionization tandem mass spectrometry (UHPLC-HRESI-MS/MS) lipid analysis. Major triacylglycerols (TAG) were detected already at early developmental stages, albeit at low abundance. The decrease of FFA during kernel filling corresponded to accumulation of predominantly linoleate (C18:2n6)-containing C52 and C54 TAG. Fatty acid composition of polar lipids including phospholipids and galactolipids also showed the progressive dominance of linoleate, typically since two weeks after anthesis. Conversely, minor sphingolipids (ceramides and glycosylceramides) were constituted mainly by saturated long chain FA, also oxygenated, combined with a restricted set of sphingoid bases, and might play a signaling role during grain development.

Diatoms are eukaryotic microalgae that play a pivotal role in biological and geochemical marine cycles. These microorganisms are at the basis of the trophic chain and their lipids are essential components (e.g. eicosapentaenoic acid, EPA) of aquatic food webs. Galactolipids are the primary lipid components of plastid membranes and form the largest lipid family of diatoms. As source of polyunsaturated fatty acids (PUFAs), these compounds are also involved in the synthesis of lipoxygenase (LOX) products such as non-volatile oxylipins and polyunsaturated aldehydes. Here, we report the first identification of two genes, namely PmLAH1 and PaLAH1, coding for lipolytic enzymes in two diatoms of the genus Pseudo-nitzschia. Functional and modeling studies evidence a patatin-like domain endowed with galactolipase and phospholipase activity at the C-terminus of both proteins. Homologues of Pseudo-nitzschia LAH1 genes were retrieved in other diatom species so far sequenced in agreement with conservation of the functional role of these proteins within the lineage.

Proteomics was exploited to assess the nature of possible traces of vomit found on the scene of an alleged sexual assault. In the case in point, a woman reported to the police to be raped five days before by a cousin of hers in his car. The woman declared she had vomited in the car before fainting definitely, due to alcohol or possible drugs covertly slipped in her drinks. The suspect confirmed the sexual intercourse, but he claimed consensual sex while the woman was fully conscious. To establish consent and hence subsistence of the crime, the Magistrate requested toxicological analyses on items sampled from the car and from woman's boots. Negative results obtained from toxicological analyses could not exclude the actual assumption of psychoactive substances by the alleged victim, due to sample aging. On the contrary, proteomic analysis disclosed a pattern of 249 gene products including signature endogenous and food-derived proteins along with a multitude of peptide digests, clearly indicative of vomit, thereby supporting the victim's report in the case under examination. Proteomics also provided detailed information about the nature of meal, which might contribute to frame the crime scene in similar cases. SIGNIFICANCE: The identification of traces of vomit supported the report of the victim's report according to which she vomited before definitely losing consciousness, so providing key contribution to establish consent for the sexual intercourse. This is the first time that proteomics is used to identify traces of vomit for forensic purposes. In spite of the scantiness of the biological specimen available, proteomics was successful to define a panel of characteristic endogenous proteins as well as to identify partly digested food-proteins arising from a complex meal. Proteomics is increasingly used as a forensic technique, well complementing the existing tools. In general, assessing traces of vomit in biological specimens and characterizing the nature of food ingested at the molecular level could afford probative elements to frame a crime scene.

The aim of the present study was to identify and characterize the celiacogenic/immunogenic proteins and peptides released during digestion of pasta (Triticum durum semolina). Cooked pasta was digested using a harmonized in vitro static model of oral-gastro-duodenal digestion. The course of pasta protein digestion was monitored by SDS-PAGE, and gluten proteins were specifically analyzed by Western blot using sera of celiac patients. Among the allergens, nonspecific lipid-transfer protein was highly resistant to gastroduodenal hydrolysis, while other digestion-stable allergens such as alpha-amylase/trypsin inhibitors were not detected being totally released in the pasta cooking water. To simulate the final stage of intestinal degradation, the gastroduodenal digesta were incubated with porcine jejunal brush-border membrane hydrolases. Sixty-one peptides surviving the brush-border membrane peptidases were identified by liquid chromatography-mass spectrometry, including several gluten-derived sequences encrypting different motifs responsible for the induction of celiac disease. These results provide new insights into the persistence of wheat-derived peptides during digestion of cooked pasta samples.

Enzymatic dough improvers (DIs) are increasingly used as baking co-adjuvants. Herein, an array of techniques, including Western blotting, PCR, electrophoresis-based and shotgun proteomics, was addressed to identify the enzymes in six commercial DI preparations. In particular, this work sought to exclude the possible undeclared use of amylolytic enzymes from porcine (or other animal origin) pancreas in DIs. PCR-amplified mitochondrial cytochrome b (mt cyt b) gene region and porcine pancreatic α-amylase were the targets of DNA-based and protein methods, respectively, both assuring a limit of detection lower than 0.5-0.1% (w/w). Aspergillum oryzae α-amylase and Hordeum vulgare (barley) β-amylase were the most represented enzymes in all DI samples. Although one sample was PCR-positive, none among the DIs contained porcine pancreatic enzymes. Comparative gas chromatographic analysis of fatty acids suggested that the porcine contamination might arise from hard fats of porcine origin (lard), emphasizing the need of performing analyses at the protein level when the targets are enzymes or proteins.

A "virtual two-dimensional (2D)-like" approach based on pH 2.5-6.0 gel isoelectrofocusing coupled to MALDI-TOF mass spectrometry (MS) was addressed for challenging the ovine casein heterogeneity due to polymorphism and post-translational modifications. The procedure enabled the identification of the main casein components including i) the four casein families at different degrees of phosphorylation, ii) nonallelic variants of either alpha(s1)- or alpha(s2)-CN, iii) differently glycosylated kappa-CN, and iv) high molecular mass proteolytic peptides. Protein assignment was confirmed by MALDI-TOF (MS) mass mapping of the tryptic digests, while phosphorylation sites were localized by tandem mass spectrometry. A straightforward identification was hindered by unexpected molecular mass shifts due to the oxidization of alpha(s1)- and the beta-CN. Indeed, using nano-ESI-MS, the casein sub-types were proved to contain a variable number of oxidized methionine residues. Data were additionally substantiated using polyclonal antibodies raised against the single casein families for immunolabelling purposes. The outcomes herein demonstrate the potentiality of the "virtual 2D-like" approach and provide indications useful for the inter-laboratory discrepancies in casein identification. They also greatly facilitate the comparison of data and the establishment of multi-user image-based isoelectrofocusing gels. (C) 2012 Elsevier Ltd. All rights reserved.

Owing to its extensive use in the human diet, wheat is among the most common causes of food-related allergies and intolerances. Allergies to wheat are provoked by ingestion, inhalation or contact with either the soluble or the insoluble gluten proteins in wheat. Gluten proteins, and particularly the gliadin fraction, are also the main factor triggering celiac disease, a common enteropathy induced by ingestion of wheat gluten proteins and related prolamins from oat, rye and barley in genetically susceptible individuals. The role of gliadin and of its derived peptides in eliciting the adverse reactions in celiac disease are still far from being completely explained. Owing to its unique pathogenesis, celiac disease is widely investigated as a model immunogenetic disorder. The structural characterization of the injuring agents, the gluten proteins, assumes a particular significance in order to deepen the understanding of the events that trigger this and similar diseases at the molecular level. Recent developments in proteomics have provided an important contribution to the understanding of several basic aspects of wheat protein-related diseases. These include: the identification of gluten fractions and derived peptides involved in wheat allergy and intolerance, including celiac disease, and the elucidation of their mechanism of toxicity; the development and validation of sensitive and specific methods for detecting trace amounts of gluten proteins in gluten-free foods for intolerant patients; and the formulation of completely new substitute foods and ingredients to replace the gluten-based ones. In this article, the main aspects of current and prospective applications of mass spectrometry and proteomic technologies to the structural characterization of gluten proteins and derived peptides are critically presented, with a focus on issues related to their detection, identification and quantification, which are relevant to the biochemical, immunological and toxicological aspects of wheat intolerance.

A growing interest in developing new strategies for preventing coeliac disease has motivated efforts to identify cereals with null or reduced toxicity. In the current study, we investigate the biological effects of ID331 Triticum monococcum gliadin-derived peptides in human Caco-2 intestinal epithelial cells. Triticum aestivum gliadin derived peptides were employed as a positive control. The effects on epithelial permeability, zonulin release, viability, and cytoskeleton reorganization were investigated. Our findings confirmed that ID331 gliadin did not enhance permeability and did not induce zonulin release, cytotoxicity or cytoskeleton reorganization of Caco-2 cell monolayers. We also demonstrated that ID331 omega-gliadin and its derived peptide omega(105-123) exerted a protective action, mitigating the injury of Triticum aestivum gliadin on cell viability and cytoskeleton reorganization. These results may represent a new opportunity for the future development of innovative strategies to reduce gluten toxicity in the diet of patients with gluten intolerance. (C) 2016 Elsevier Ltd. All rights reserved.

Four Lactobacillus helveticus strains were studied for proteolytic capacity and general aminopeptidase (AP) and X-Pro dipeptidyl aminopeptidase (DAP) activity. The rate of hydrolysis and the activity against synthetic substrates with N-terminal residues of Arg, Lys, Leu, Glu or Pro, varied markedly among the strains. The X-Pro DAP activity was consistently high. The crude cell-wall and cytoplasm extracts from strain Lb. helveticus ISLC59 were analysed thoroughly for their proteolysis ability by using four synthetic peptide substrates, including αs1-CN(f1-23). Peptides formed during in vitro hydrolysis of the synthetic substrates by cell wall and cytoplasm preparations were identified by LC-ESI/MS. In doing so, it was possible to infer a prevalent endopeptidase activity splitting Lys7-His8 and Gln13-Glu14 bonds in the cytoplasm, and to deduce a secondary activity, which hydrolysed Glu14-Val15, Leu16-Asn17, Glu18-Asn19 and Lys3-His4 bonds lacking in the cell-wall. The presence of exopeptidases, as mainly AP, DAP, and carboxypeptidase (CPase) was deduced from the formation of several N- and C-terminally truncated peptides sets. The AP activity was higher in the cell-wall layer, where CPase activity was absent. The in vitro assays with cell extracts of the Lb. helveticus ISLC59 strain revealed extensive exopeptidase and endopeptidase activities. In several cases, the hydrolytic system of Lb. helveticus that splits in vitro αs1-CN(f1-23) peptide bonds was similar to that of Lactococcus lactis. The effects were also compared with those occurring in vivo in hard cheese such as Grana Padano.

[Scope]: This study aimed to assess the impact of the 'often neglected' intestinal brush border membranes (BBMs) hydrolases on dietary peptides, exploring the possibility that the disintegration of proteins progressed in the small intestine up to a >core> of intrinsically stable oligopeptides, persisting independently on the up-stream breakdown. [Methods and results]: Samples of sodium caseinate, skim milk powder, and whey protein isolate were submitted to in vitro simulated gastropancreatic digestion using two different procedures: (i) a simplified model involving the main compartmental specific proteases; (ii) a static digestion method based on a frameset of parameters inferred from in vivo. The gastroduodenal digesta were further hydrolyzed with peptidases from porcine jejunal BBM. The peptidomes arising from the two digestion models, characterized by combined HPLC and MS techniques, differed to some extent. However, only specific protein domains survived digestion, among which are potential bioactive or immunogenic (food allergy) peptides. The degree of hydrolysis (DH) after BBM digestion (70-77%) practically did not differ between the digestion models and significantly increased the DH after duodenal steps. [Conclusion]: Any in vitro digestion model should be supplemented with a jejunal phase to realistically determine the bioaccessibility and bioavailability of dietary peptides., The research was in part supported by the EU Infogest COST (European Cooperation in Science and Technology) Action FA 1005 “Improving health properties of food by sharing our knowledge on the digestive process” by funding a short scientific mission of G. P. in the laboratories at CIAL-CSIC (Madrid, Spain).

Bresaola is traditionally produced by curing and air-drying entire anatomic cuts of lean bovine hindquarters. Because of its low-fat and high-protein content, Bresaola is increasingly appreciated for the nutritional properties and has become one of the best known and exported Italian meat products. Both sarcoplasmic and myofibrillar protein fractions of Bresaola are extensively hydrolyzed by endogenous proteases, since the early post mortem, releasing a large variety of peptides many of which can exert several biological activities in human body. When ingested, Bresaola proteins and (poly)peptides are further degraded by gastrointestinal (GI) proteases. With the aim to identify bovine muscle-derived proteins and peptides surviving digestion, two Bresaola samples (one with and one without the Protected Geographical Indication label) were subjected to a static in vitro model of digestion that included the sequential oral, gastric and duodenal phases. The "digestomes" were characterized by mass spectrometry-based proteomic and peptidomic strategies. Aside from slight differences, probably related to the different nature of the raw material and to different technological processes, the great part of the peptides released at the end of digestion was common to the two samples. Sarcoplasmic proteins were promptly degraded, whereas myofibrillar chains require a previous proteolytic release and are not completely hydrolyzed by gastro-duodenal proteases even after prolonged hydrolysis. More than 170 peptides liberated from the major structural (actin, myosin) and sarcoplasmic muscle proteins were identified. Several among these peptides are or are precursor of potentially antihypertensive or antioxidant sequences. (C) 2014 Published by Elsevier Ltd.

The comprehensive analysis of natural lipid mixtures is often challenging due to the simultaneous occurrence of functionally and structurally heterogeneous compounds. Modern analytical approaches in system-wide lipidomics essentially rely on mass spectrometry (MS). The overabundant amount of triacylglycerols (TAGs) in most samples hinders the direct detection of phospholipids (PLs) or other low-abundance lipids; therefore, a fractionation step is most often required to reduce sample complexity prior to MS analysis. In this work, we explore the use of hydroxyapatite (HAP) as a chromatographic stationary phase (gel HAP) or chemo-affinity sorbent material (ceramic HAP) to selectively enrich PLs and polar lipids from chicken egg yolk and buttermilk. Due to the affinity of phosphate-containing compounds for HAP, both in-column and in-batch HAP-based chromatography were effective to deplete TAGs before releasing PLs with an eluting ternary system containing sodium phosphate as the displacing agent. Buttermilk gangliosides and PLs co-eluted, indicating that HAP also exhibits a high affinity for sialylated glycolipids and that polar lipids are retained through a combined mechanism of chemo-affinity and hydrogen bonding. To the best of our knowledge, this is the first report in which HAP is proposed as an alternative stationary phase for separating both the PLs and sialylated glycolipids from TAGs in complex lipidomes. The HAP-based chromatography has potential to be improved for the separation of the polar lipid classes. (C) 2014 Elsevier B.V. All rights reserved.

Transport across monolayers of human colon adenocarcinoma (Caco-2) cells represents one of the most widely accepted in vitro models of the intestinal uptake of nutrients and drugs. Herein, the entire panel of peptides produced from caseins (CN) and whey proteins (WP) that survive in vitro sequential gastro-pancreatic digestion and translocate across the Caco-2 monolayers have been characterized by high-performance liquid chromatography (HPLC) and mass spectrometry (MS). Except for traces of casein phosphopeptides, we did not detect any milk-derived peptides with proposed bioactivity. The absorption behavior of two resistant ?-Lactoglobulin (?-Lg) domains, ?- Lg 125-135 and ?-Lg 40-60, was studied in detail using synthetic peptides. The IgE-binding properties of the peptide digests and synthetic peptides recovered from both the apical and basolateral compartments of the monolayers were evaluated by a dot-immunobinding assay using the sera of children (N=5) diagnosed with cow's milk allergy. Outcomes indicated that ?-Lg 127- 135, which is a Caco-2 processed form of ?-Lg 125-135, is a possible "immune sensitizing factors" in vivo. The almost complete loss of the IgE-binding affinity of both CN and WP after enzymatic digestion and transepithelial transport also points out the need of designing in vivo experiments to track the metabolic fate of dietary proteins.

7 páginas, 6 figuras., Soybean (Glycine max) 7S β-conglycinin is a seed storage protein consisting of homo- and hetero-trimers of three subunits, namely α (~67kDa), α' (~71kDa), and β (~50kDa), non-covalently associated. The N-glycans released from the whole β-conglycinin have been already characterized by 1H NMR some decades ago. Nevertheless, the actual glycosylation of the potential sites and the glycoforms of the individual subunits have not been specifically investigated so far. In this study, up-to-date chromatographic, electrophoretic and mass spectrometric strategies have been combined to achieve the structural characterization of the glycoforms of the three individual β-conglycinin subunits. Glycosylation sites were assigned by analyzing the tryptic glycopeptides of the isolated subunits. Underivatized N-glycans were purified with a two-step clean-up, consisting in sequential reversed-phase and activated porous graphitized carbon micro-chromatography, and profiled by matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS). © 2013 Elsevier B.V., The present research has been supported by the projects Italy-Spain Integrate Action (IT2009-0087, IT10ESiFCF2) and CONSOLIDER Ingenio 2010 (FUN-C-FOOD): CSD 2007-00063). Dr. M.A.-B. thanks CSIC and European Social Funds for her JAEdoc contract.

Hazelnuts (Corylus avellana) are one of the most common sources of life-long IgE-mediated food allergies. In this study, we investigated the IgE-reactivity pattern of children with hazelnut allergy (N = 15) from Regione Campania, located in Southern Italy, and addressed proteomic strategies for characterizing IgE-binding proteins. For all of the patients (15/15), the predominant IgE-reactive component was a minor ~ 55 kDa protein not previously described. Similar to the hazelnut 11S globulin Cor a 9 allergen, the immunoreactive protein consisted of two subunits linked via a disulfide bridge. In contrast to Cor a 9, only the 20.7 kDa alkaline subunit exhibited IgE-affinity. The immunogenic subunit was purified by a two-step chromatographic procedure, but peptide mass fingerprinting was unsuccessful in identifying it, due to the incompleteness of the annotated hazelnut genome. Several tryptic peptides were de novo sequenced by tandem mass spectrometry and showed a high degree of homology with the 11S globulin storage proteins from other seeds, some of which have already been reported as food allergens. The structural characterization suggests that the new putative allergen is a divergent isoform of the hazelnut 11S globulin. These results provide a new platform for developing innovative diagnostic and therapeutic intervention plans. Biological significance Over the years, at least five proteins have been reported as potential food hazelnut allergens. The predominance of specific allergens appears to be strictly related to the geographical origin of the allergic subjects. The complex patterns of the IgE-reactivity of hazelnut storage proteins result in a poor diagnostic and prognostic accuracy. In the perspective of a component-resolved “molecular approach” to the hazelnut allergy we investigated the immune-reactivity patterns to hazelnuts of 15 patients (14 in the pediatric age range) from Region Campania, located in Southern Italy. For all the patients the predominant IgE-reactive component was a minor ~ 55 kDa protein not previously annotated in either protein or genomic databases. The putative allergen was isolated, partially characterized by MS/MS de novo sequencing and appears to be an isoallergen of the hazelnut 11S globulin Cor a 9. Like this latter, the immunoreactive protein consisted of two subunits linked via a disulfide. In contrast to Cor a 9, only the 20.7 kDa alkaline subunit exhibited IgE-affinity, in analogy to 11S allergens from other seeds (pistachio, cashew, soybean). We believe that the application of combined immunochemical and proteomic strategies to characterize the new food allergen could be of interest for the readers of Journal of Proteomics. In addition, the results of this study have functional worth in providing a new platform to plan innovative diagnostic and therapeutic intervention approaches to treat hazelnut allergy.

Celiac disease is a chronic enteropathy caused by the ingestion of wheat gliadin and other cereal prolamines. The synthetic peptides 31-43 (P31-43) and 31-49 (P31-49) from A-gliadin are considered to be model peptides for studying innate immunity in celiac disease. Our previous study demonstrated that P31-43 and P31-49 are encrypted within peptide 31- 55 (P31-55), which is naturally released from gastropancreatic digestion and is not susceptible to hydrolysis by brush border membrane enzymes. Here, we analyzed the permeability of P31-55 through the epithelial cell layer of confluent Caco-2 cells using high-performance liquid chromatography, mass spectrometry, and fluorescence-activated cell sorting. Twenty-three percent of the P31-55 added to the apical chamber was transported to the basolateral chamber after 4 h of incubation without being degraded by hydrolysis. Treatment of Caco-2 cells with whole gliadin digests extracted from a common wheat cultivar increased the epithelial P31-55 translocation by approximately 35%. Moreover, we observed an atypical chromatographic profile consisting of a double peak. Chromatography using different column temperatures and circular dichroism highlighted the presence of more conformational structures around the amide bond of the two adjacent prolines 38 and 39. These findings confirm that P31-55 is gastrointestinally resistant and is permeable across a Caco-2 monolayer. Moreover, we hypothesize that the various conformations of P31-55 may play a role in the activation of innate immunity.

Microbial transglutaminase is used in the food industry to improve texture by catalyzing protein cross-linking. Casein is a well-known transglutaminase substrate, but the complete role of glutamine (Q) and lysine (K) residues in its cross-linking is not fully understood. In this study, we describe the characterization of microbial Transglutaminase -modified casein using a combination of immunological and proteomic techniques. Using 5-(biotinamido)pentylamine as an acyl acceptor probe, three Q residues of β-casein and one of αs1-casein were found to participate as acyl donors. However, no Q-residues were involved in network formation with κ-casein or αs2-casein. Q and K residues in the e-(γ-glutamyl)lysine-isopeptide bonds β-casein were identified by nanoelectrospray tandem mass spectrometry of the proteolytic digests. This work reports our progress toward a better understanding of the function and mechanism of action of microbial transglutaminase-mediated proteins. The results suggest a possible role for transglutaminase in the formation of casein micelles.

In the last years proteomic science has started to provide an important contribution to the disclosure of basic aspects of food-related diseases. Among these, the identification of proteins involved in food allergy and their mechanism of activation of toxicity. Elucidation of these key issues requires the integration of clinical, immunological, genomic and proteomic approaches. These combined research efforts are aimed to obtain structural and functional information to assist the development of novel, more reliable and powerful diagnostic protocols alternative to the currently available procedures, mainly based on food challenge tests. Another crucial aspect related to food allergy is the need for methods to detect trace amounts of allergenic proteins in foods. Mass spectrometry is the only non-immunological method for high-specificity and high-sensitivity detection of allergens in foods. Nowadays, once provided the appropriate sample handling and the correct operative conditions, qualitative and quantitative determination of allergens in foods and ingredients can be efficiently obtained by MALDI-TOF-MS and LC–MS/MS methods, with limits of detection and quantification in the low-ppb range. The availability of accurate and fast alternatives to immunological ELISA tests may also enable the development of novel therapeutic strategies and food processing technologies to aid patients with food allergy or intolerance, and to support allergen labelling and certification processes, all issues where the role of proteomic science is emerging.

Resistance to proteases throughout the gastrointestinal (GI) tract is a prerequisite for milk-derived peptides to exert biological activities. In this work an in vitro multi-step static model to simulate complete digestion of the bovine milk proteins has been developed. The experimental set-up involved the sequential use of: (i) pepsin, (ii) pancreatic proteases, and (iii) extracts of human intestinal brush border membranes, in simulated gastric, duodenal and jejuneal environments, respectively. Enzymatic concentrations and reaction times were selected in order to closely reproduce the in vivo conditions. The aim was to identify the peptide candidates able to exhibit significant bioactive effects. Casein and whey protein peptides which survived the in vitro GI digestion have been identified by the combined application of HPLC and mass spectrometry techniques. While the permanence of the main potentially bioactive peptides from both casein and whey proteins was found of limited physiological relevance, the high resistance to proteolysis of specific regions of beta-lactoglobulin (beta-Lg), and especially that of the peptide beta-Lg f125-135, could have implications for the immunogenic action of beta-Lg in the insurgence of cow's milk allergy.

The most challenging analytical task facing phosphoproteome determination requires the isolation of phosphorylated peptides from the myriad of unphosphorylated species. In the past, several strategies for phosphopeptide isolation have been proposed in combination with subsequent mass spectrometric investigations. Among these techniques, immobilized metal affinity chromatography and titanium dioxide have been recognized as the most effective. Here, we present an alternative method for the enrichment of phosphopeptides based on hydroxyapatite (HAP) chromatography. By taking advantage of the strong interaction of HAP with phosphate and calcium ions, we developed an efficient method for the selective separation and fractionation of phosphorylated peptides. The effectiveness and efficiency of recovery for this procedure was assayed using tryptic digests of standard phosphorylated protein mixtures. Based on the higher affinity of multi-phosphorylated peptides for HAP surfaces, the introduction of a phosphate buffer gradient for stepwise peptide elution resulted in the separation of mono-, di-, tri-, and multi-phosphorylated peptides. Thus, we demonstrated that this technique is highly selective and independent of the degree of peptide phosphorylation.

Mass spectrometry has arguably become the core technology for the characterization of food proteins and peptides. The application of mass spectrometry-based techniques for the qualitative and quantitative analysis of the complex protein mixtures contained in most food preparations is playing a decisive role in the understanding of their nature, structure, functional properties and impact on human health. The application of mass spectrometry to protein analysis has been revolutionized in the recent years by the development of soft ionization techniques such as electrospray ionization and matrix assisted laser desorption/ionization, and by the introduction of multi-stage and ‘hybrid’ analyzers able to generate de novo amino acid sequence information. The interfacing of mass spectrometry with protein databases has resulted in entirely new possibilities of protein characterization, including the high sensitivity mapping (femtomole to attomole levels) of post-translational and other chemical modifications, protein conformations and protein–protein and protein–ligand interactions, and in general for proteomic studies, building up the core platform of modern proteomic science. MS-based strategies to food and nutrition proteomics are now capable to address a wide range of analytical questions which include issues related to food quality and safety, certification and traceability of (typical) products, and to the definition of the structure/function relationship of food proteins and peptides. These different aspects are necessarily interconnected and can be effectively understood and elucidated only by use of integrated, up-to-date analytical approaches. In this review, the main aspects of current and perspective applications of mass spectrometry and proteomic technologies to the structural characterization of food proteins are presented, with focus on issues related to their detection, identification, and quantification, relevant for their biochemical, technological and toxicological aspects.

Udgivelsesdato: 2008-Sep Breastfeeding is now generally recognized as a critical factor in protecting newborns against infections. An important mechanism responsible for the antibacterial and antiviral effects of breast milk is the prevention of pathogen adhesion to host cell membranes mediated by a number of glycoconjugates, also including glycoproteins. A number of approaches to describe the complexity of human milk proteome have provided only a partial characterization of restricted classes of N-linked glycoproteins. To achieve this objective, profiling N-linked glycoproteins of human milk was performed by Hydrophilic Interaction LC (HILIC) and MS analysis. Glycopeptides were selectively enriched from the protein tryptic digest of human milk samples. Oligosaccharide-free peptides obtained by peptide N-glycosidase F (PNGase F) treatment were characterized by a shotgun MS-based approach, allowing the identification of N-glycosylated sites localized on proteins. Using this strategy, 32 different glycoproteins were identified and 63 N-glycosylated sites encrypted in them were located. The glycoproteins include immunocompetent factors, membrane fat globule-associated proteins, enzymes involved in lipid degradation and cell differentiation, specific receptors, and other gene products with still unknown functions.

Prolonged exposure (>90 days) of bovine β-lactoglobulin (BLG) to subdenaturing concentrations of either urea or potassium thiocyanate resulted in the formation of ordered polymers in the form of fibrils. The fibrils obtained with each chaotrope showed major differences in morphology, surface properties, thiol accessibility, and stability to dissociating agents as a consequence of the different chemical bonds involved in their stabilization. Hydrophobic interactions between BLG monomers are predominant in thiocyanate-formed fibrils, whereas urea-formed fibrils are stabilized by intermolecular disulfides generated through a thiol-disulfide exchange reaction. The different features of fibrils obtained with each chaotrope relate to the peculiar structural features and chemical properties of the “active” monomers generated by subdenaturing chaotrope concentrations in the early phases of the polymerization process, as detected by spectroscopic and limited proteolysis/mass spectrometry studies in the earliest stages of the action of individual chaotropes. The chaotrope-specific features of these early intermediates in turn affect the polymerization mechanism, whose intermediates were studied by size-exclusion chromatography on the soluble fraction at different times of fibril formation. The potential of these findings for the production of protein-derived nanostructures having different and controlled geometries and chemical properties is also discussed. © 2007 Wiley Periodicals, Inc. Biopolymers 86: 57–72, 2007. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com

In Azotobacter vinelandii the rhdA gene codes for a protein (RhdA) of the rhodanese-homology superfamily. By combining proteomics, enzymic profiles and ultrastructural observations, the phenotype of an A. vinelandii rhdA mutant was analyzed. We found that the A. vinelandii rhdA mutant, and not the wild-type strain, accumulated polyhydroxybutyrate. RhdA deficiency enhanced the expression of enzymes of the polyhydroxybutyrate biosynthetic operon, and affected the activity of specific tricarboxylic acid cycle enzymes. The effect was dramatic on aconitase, in spite of comparable expression of aconitase polypeptides in both strains. By using a model system, we found that RhdA triggered protection from oxidants.

In the present study, an alternative procedure for two-dimensional (2D) electrophoretic analysis in proteomic investigation of the most represented basic muscle water-soluble proteins is suggested. Our method consists of Acetic acid-Urea-Triton polyacrylamide gel (AUT-PAGE) analysis in the first dimension and standard sodium dodecyl sulphate polyacrylamide gel (SDS-PAGE) in the second dimension. Although standard two-dimensional Immobilized pH Gradient-Sodium Dodecyl-Sulphate (2D IPG-SDS) gel electrophoresis has been successfully used to study these proteins, most of the water-soluble proteins are spread on the alkaline part of the 2D map and are poorly focused. Furthermore, the similarity in their molecular weights impairs resolution of the classical approach. The addition of Triton X-100, a non-ionic detergent, into the gel induces a differential electrophoretic mobility of proteins as a result of the formation of mixed micelles between the detergent and the hydrophobic moieties of polypeptides, separating basic proteins with a criterion similar to reversed phase chromatography based on their hydrophobicity. The acid pH induces positive net charges, increasing with the isoelectric point of proteins, thus allowing enhanced resolution in the separation. By using 2D AUT-PAGE/SDS electrophoresis approach to separate water-soluble proteins from fresh pork and from dry-cured products, we could spread proteins over a greater area, achieving a greater resolution than that obtained by IPG in the pH range 3-10 and 6-11. Sarcoplasmic proteins undergoing proteolysis during the ripening of products were identified by Matrix Assisted Laser Desorption/Ionization-Time of Flight (MALDI-ToF) mass spectrometry peptide mass fingerprinting in a easier and more effective way. Two-dimensional AUT-PAGE/SDS electrophoresis has allowed to simplify separation of sarcoplasmic protein mixtures making this technique suitable in the defining of quality of dry-cured pork products by immediate comparison of 2D maps to define the events occurring during their ripening and individuate candidate molecular markers of the characteristic proteolytic processes. Considering that, essentially, muscle endogenous enzymic activity, calpains and cathepsins, occur in the ripening process of dry-cured ham, whereas a combined action between endogenous and microbial enzymes takes place in the case of sausage ripening, these results provide deeper insight into the respective role of endogenous and microbial enzymes in performing proteolysis. Finally, image analysis and creation of data bank could be achieved to quickly identify and protect typical products.

We have investigated the molecular mechanisms that produce different structural and functional behavior in the monomeric and trimeric forms of seminal vesicle protein no. 4, a protein with immunomodulatory, anti-inflammatory, and procoagulant activity secreted from the rat seminal vesicle epithelium. The monomeric and trimeric forms were characterized in solution by CD. Details of the self-association process and structural changes that accompany aggregation were investigated by different experimental approaches: trypsin proteolysis, sequence analysis, chemical modification, and computer modeling. The self-association process induces conformational change mainly in the 1-70 region, which appears to be without secondary structure in the monomer but contains alpha-helix in the trimer. In vivo, proteolysis of seminal vesicle protein no. 4 generates active peptides and this is affected by the monomer/trimer state, which is regulated by the concentration of the protein. The information obtained shows how conformational changes between the monomeric and trimeric forms represent a crucial aspect of activity modulation.

We report a fast and easy-to-use procedure that combines polyacrylamide gel electrophoresis with matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF) and nanoelectrospray-tandem mass spectrometry (nES-MS/MS) analysis for the identification of casein components and defined phosphorylated sites. This methodology ensured identification of more than 30 phosphorylated proteins, five beta-, fifteen alpha(s1)-, ten alpha(s2)-, and four kappa-casein (CN) components, including nonallelic, differently phosphorylated, and glycosylated forms. The sugar motif covalently bound to kappa-CN was identified as chains, trisaccharide GalNAc, Gal, NeuGc, and tetrasaccharide 1GalNAc, 1Gal, 2NeuGc. Also identified was a biantennary chain made up of both chains of trisaccharide 1GalNAc, 1Gal, 1NeuGc, and tetrasaccharide 1GalNAc, 1Gal, 2NeuGc moiety on a single kappa-CN component. The phosphate group on site Ser12 of tryptic peptide 8-22 of most phosphorylated alpha(s1)-CN (11 phosphate groups) was localized and the oligosaccharide sequence of the main tryptic glycopeptides of two kappa-CN components was determined by means of MS/MS analysis.

The entry of the human immunodeficiency virus into cells requires the interaction of the viral envelope glycoprotein gp120 with CD4 and a chemokine receptor. The gp120 binding site has been previously mapped to the Ig-CDR2-like region of CD4 first domain. A second area of this domain (Ig-CDR3-like region) is involved in gp120-CD4 interactions, but its gp120 counterpart remained so far unknown. Using a photoaffinity labeling experiment, we demonstrate that a peptide, mapping the (307-330)m region of HIV-MN-gp120 V3 loop, binds a sequence including a part of the Ig-CDR3-like region. These results may contribute to explain the complex mechanism of human immunodeficiency virus penetration, helping the development of new therapeutic agents.

The occurrence of rhodanese-like proteins in the major evolutionary phyla, together with the observed abundance of these proteins also within the same genome, suggests that their function cannot be limited to cyanide scavenging. The aim of the present study was to investigate whether Azotobacter vinelandii RhdA, an enzyme possessing unique biochemical and structural features with respect to other members of rhodanese homology superfamily, could recognize a suitable protein as a potential acceptor of the sulfane sulfur held on its catalytic Cys residue. Both the potential sulfur-delivery RhdA-S and the sulfur- deprived RhdA were found to interact with either holo- or apo-adrenodoxin, the 'substrate' protein used in this work. Interaction of RhdA-S with apoadrenodoxin led to mobilization of RhdA-S sulfane sulfur. Under appropriate conditions, the sulfur released from RhdA-S was productively used for 2Fe 2S cluster reconstitution to yield holo-adrenodoxin from apo-adrenodoxin in the absence of any other sulfur source. A comparison of the reactivity of RhdA-S with protein and non-protein thiols allowed also some insights into the accessibility of the sulfane sulfur carried by RhdA.