Nonspecific lipid-transfer proteins in plant foods and pollens: an important allergen class

Genome-wide characterization, chromosome localization, and expression profile analysis of poplar non-specific lipid transfer proteins

Plant non-specific lipid transfer proteins (nsLTPs) are small and have a broad biological function involved in reproductive development and abiotic stress resistance. Although a small part of plant nsLTPs have been identified, these proteins have not been characterized in poplar at the genomic level. A genome-wide characterization and expression identification of poplar nsLTP members were performed in this study. A total of 42 poplar nsLTP genes were identified from the poplar genome. A comprehensive analysis of poplar nsLTPs was conducted by a phylogenetic tree, duplication events, gene structures, and conserved motifs. The cis-elements of poplar nsLTPs were predicted to respond to light, hormone, and abiotic stress. Many transcription factors (TFs) were identified to interact with poplar nsLTP cis-elements. The tested poplar nsLTPs were expressed in leaves, stems, and roots, but their expression levels differed among tested tissues. Most poplar nsLTP expression levels were changed by abiotic stress, implying that poplar nsLTP may be involved in abiotic stress resistance. Network analysis showed that poplar nsLTPs are putative genes involved in fatty acid (FA) metabolism. This research provides sight into the further study to explain the regulatory mechanism of the poplar nsLTPs.

Identification of Major B-Cell Linear Epitopes of Peach Allergen Pru p 3 Using Immune Slot-Blot Microarray Assay

Pru p 3, one of the most representative proteins of the lipid transfer proteins (LTPs), is responsible for clinical allergic reactions to food of peach origin. The identification of Pru p 3 epitopes is not comprehensive due to different methods and principles of epitope screening. In addition, evaluation of the stability of the epitopes and the validation of the immunological key amino acids still need further research. Therefore, in the present study, an immune slot-blot microarray assay was performed to screen the epitopes from Pru p 3 overlapping peptide library, and a new epitope (P-1, AA1-16, ITCGQVSSALAPCIPY) was identified and two identified epitopes were deeply investigated (P-2, AA12-27, PCIPYVRGGGAVPPAC; P-3, AA23-38, VPPACCNGIRNVNNLA). The stability of these epitopes was then verified by thermal processing treatment and digestion experiments. Moreover, the key amino acids of the three identified epitopes were obtained by epitope amino acid mutation combined with slot-blot experiments. These findings may contribute to the further understanding of Pru p 3 and the prevention of peach allergy.

Food Allergy and Intolerance: A Narrative Review on Nutritional Concerns

Adverse food reactions include immune-mediated food allergies and non-immune-mediated intolerances. However, this distinction and the involvement of different pathogenetic mechanisms are often confused. Furthermore, there is a discrepancy between the perceived vs. actual prevalence of immune-mediated food allergies and non-immune reactions to food that are extremely common. The risk of an inappropriate approach to their correct identification can lead to inappropriate diets with severe nutritional deficiencies. This narrative review provides an outline of the pathophysiologic and clinical features of immune and non-immune adverse reactions to food-along with general diagnostic and therapeutic strategies. Special emphasis is placed on specific nutritional concerns for each of these conditions from the combined point of view of gastroenterology and immunology, in an attempt to offer a useful tool to practicing physicians in discriminating these diverging disease entities and planning their correct management. We conclude that a correct diagnostic approach and dietary control of both immune- and non-immune-mediated food-induced diseases might minimize the nutritional gaps in these patients, thus helping to improve their quality of life and reduce the economic costs of their management.

Almond allergens: update and perspective on identification and characterization

Almond (Prunus dulcis) is not only widely used as a human food as a result of its flavor, nutrients, and health benefits, but it is also one of the most likely tree nuts to trigger allergies. Almond allergens, however, have not been studied as extensively as those of peanuts and other selected tree nuts. This review provides an update of the molecular properties of almond allergens to clarify some confusion about the identities of almond allergens and our perspective on characterizing putative almond allergens. At present, the following almond allergens have been designated by the World Health Organization/International Union of Immunological Societies Allergen Nomenclature Sub-Committee: Pru du 3 (a non-specific lipid transfer protein 1, nsLTP1), Pru du 4 (a profilin), Pru du 5 (60S acidic ribosomal protein 2), Pru du 6 (an 11S legumin known as prunin) and Pru du 8 (an antimicrobial protein with cC3C repeats). Besides, almond vicilin and almond γ-conglutin have been identified as food allergens, although further characterization of these allergens is still of interest. In addition, almond 2S albumin was reported as a food allergen as a result of the misidentification of Pru du 8. Two more almond proteins have been called allergens based on their sequence homology with known food allergens and their 'membership' in relevant protein families that contain allergens in many species. These include the pathogenesis related-10 protein (referred to as Pru du 1) and the thaumatin-like protein (referred to as Pru du 2). Almonds thus have five known food allergens and five more likely ones that need to be investigated further. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

An Arabidopsis DISEASE RELATED NONSPECIFIC LIPID TRANSFER PROTEIN 1 is required for resistance against various phytopathogens and tolerance to salt stress

Synchronous and timely regulation of multiple genes results in an effective defense response that decides the fate of the host when challenged with pathogens or unexpected changes in environmental conditions. One such gene, which is downregulated in response to multiple bacterial pathogens, is a putative nonspecific lipid transfer protein (nsLTP) of unknown function that we have named DISEASE RELATED NONSPECIFIC LIPID TRANSFER PROTEIN 1 (DRN1). We show that upon pathogen challenge, DRN1 is strongly downregulated, while a putative DRN1-targeting novel microRNA (miRNA) named DRN1 Regulating miRNA (DmiR) is reciprocally upregulated. Furthermore, we provide evidence that DRN1 is required for defense against bacterial and fungal pathogens as well as for normal seedling growth under salinity stress. Although nsLTP family members from different plant species are known to be a significant source of food allergens and are often associated with antimicrobial properties, our knowledge on the biological functions and regulation of this gene family is limited. Our current work not only sheds light on the mechanism of regulation but also helps in the functional characterization of DRN1, a putative nsLTP family member of hitherto unknown function.

Nickel allergy in lipid transfer protein sensitized patients: Prevalence and clinical features

Nickel (Ni), the main responsible for allergic contact dermatitis worldwide, is also involved in systemic condition called "Systemic Nickel Sulfate Allergy Syndrome (SNAS)." Likewise, IgE-mediated reactivity to Lipid Transfer Protein (LTP) represents the main cause of primary food allergy in adults of Mediterranean countries. We evaluated the prevalence of SNAS in LTP allergic patients and investigated patients' clinical features with double sensitization (LTP and Ni). A retrospective, single-center, observational study was conducted performing a complete allergological work-up including: (1) skin prick tests; (2) serum specific IgE for plant food allergens and rPru p3 (LTP); (3) patch test with 5% Ni sulfate in petrolatum. We enrolled 140 LTP allergic patients of which 36 patients (25.7% of sample) showed additional positivity to Ni patch test. Patients with double sensitization were more frequently females and reported fewer cutaneous symptoms. Higher values of sIgE for peach, apple, peanut, walnut, grain, corn, and garlic were found in LTP allergic patients, while higher values for hazelnut in the other subgroup. The prevalence of SNAS in the LTP allergic population is clinically relevant. Moreover, the clinical and immunological profiles of patients with double sensitization were different from patients monosensitized to LTP.

Non-specific lipid transfer proteins in plants: presenting new advances and an integrated functional analysis

Plant non-specific lipid-transfer proteins (nsLTPs) are small, basic proteins present in abundance in higher plants. They are involved in key processes of plant cytology, such as the stablization of membranes, cell wall organization, and signal transduction. nsLTPs are also known to play important roles in resistance to biotic and abiotic stress, and in plant growth and development, such as sexual reproduction, seed development and germination. The structures of plant nsLTPs contain an eight-cysteine residue conserved motif, linked by four disulfide bonds, and an internal hydrophobic cavity, which comprises the lipid-binding site. This structure endows stability and increases the ability to bind and/or carry hydrophobic molecules. There is growing interest in nsLTPs, due to their critical roles, resulting in the need for a comprehensive review of their form and function. Relevant topics include: nsLTP structure and biochemical features, their classification, identification, and characterization across species, sub-cellular localization, lipid binding and transfer ability, expression profiling, functionality, and evolution. We present advances, as well as limitations and trends, relating to the different topics of the nsLTP gene family. This review collates a large body of research pertaining to the role of nsLTPs across the plant kingdom, which has been integrated as an in depth functional analysis of this group of proteins as a whole, and their activities across multiple biochemical pathways, based on a large number of reports. This review will enhance our understanding of nsLTP activity in planta, prompting further work and insights into the roles of this multifaceted protein family in plants.

Lipid transfer protein sensitization: reactivity profiles and clinical risk assessment in an Italian cohort

BACKGROUND

Nonspecific lipid transfer proteins (nsLTPs) represent a major cause of systemic food allergic reactions in the Mediterranean area. This study investigate hierarchical patterns and cluster relationships of IgE sensitization to different nsLTPs, and the relationship to clinical allergy in a large Italian cohort.

METHODS

A total of 568 nsLTP-positive subjects after IgE ImmunoCAP-ISAC microarray analysis with Ara h 9, Art v 3, Cor a 8, Jug r 3, Pla a 3, Pru p 3 and Tri a 14 allergens were studied. IgE inhibition experiments were carried out with mugwort and plane tree pollen extracts.

RESULTS

Eighty-two per cent of nsLTP-positive participants (94% if <6 years old) were Pru p 3(pos) , and 71% were Jug r 3(pos) . Participants who reacted to >5 nsLTPs reported a higher incidence of food-induced systemic reactions. Only Art v 3 and Pla a 3 (mugwort and plane tree nsLTPs, respectively) were associated with respiratory symptoms, and a correlation was observed between sensitization to pollen and plant food nsLTPs, particularly between Pla a 3 and tree nut/peanut nsLTPs. Co-sensitization to Par j 2 and PR-10 or profilin pan-allergens was associated with a lower prior prevalence of severe food-induced reactions. In inhibition assays, plane and mugwort pollen extracts inhibited 50-100% of IgE binding to food nsLTPs in microarrays.

CONCLUSIONS

Testing IgE reactivity to a panel of nsLTP allergens unveils important associations between nsLTP sensitization profiles and clinical presentation and allows the identification of novel cluster patterns indicating likely cross-reactivities and highlighting potential allergens for nsLTP immunotherapy.

Unraveling the effect of arsenic on the model Medicago-Ensifer interaction: a transcriptomic meta-analysis

The genetic regulation underlying the effect of arsenic (As(III)) on the model symbiosis Medicago-Ensifer was investigated using a combination of physiological (split-roots), microscopy and genetic (microarrays, qRT-PCR and composite plants) tools. Nodulation was very sensitive to As(III) (median inhibitory dose (ID50) = 20 μM). The effect on root elongation and on nodulation was local (nonsystemic). A battery of stress (salt, drought, heat shock, metals, etc.)-related genes were induced. Glutathione played a pivotal role in tolerance/detoxification, together with secondary metabolites ((iso)flavonoids and phenylpropanoids). However, antioxidant enzymes were not activated. Concerning the symbiotic interaction, molecular evidence suggesting that rhizobia alleviate As stress is for the first time provided. Chalcone synthase (which is involved in the first step of the legume-rhizobia cross-talk) was strongly enhanced, suggesting that the plants are biased to establish symbiotic interactions under As(III) stress. In contrast, 13 subsequent nodulation genes (involved in nodulation factors (Nod factors) perception, infection, thread initiation and progression, and nodule morphogenesis) were repressed. Overexpression of the ethylene responsive factor ERN in composite plants reduced root stress and partially restored nodulation, whereas overexpression of the early nodulin ENOD12 enhanced nodulation both in the presence and, particularly, in the absence of As, without affecting root elongation. Several transcription factors were identified, which could be additional targets for genetic engineering aiming to improve nodulation and/or alleviate root stress induced by this toxic.

Lipid transfer protein syndrome: clinical pattern, cofactor effect and profile of molecular sensitization to plant-foods and pollens

BACKGROUND

Multiple plant-food sensitizations with a complex pattern of clinical manifestations are a common feature of lipid transfer protein (LTP)-allergic patients. Component-resolved diagnosis permits the diagnosis of the allergen sensitization profile.

OBJECTIVE

We sought to clinically characterize and describe the plant-food and pollen molecular sensitization profile in patients with LTP syndrome.

METHODS

Forty-five subjects were recruited, after being diagnosed with multiple plant-food allergies sensitized to LTP, but not to any other plant-food allergen, according to the molecular allergen panel tested (Pru p 3 (LTP), Pru p 1 (Bet v 1-like), Pru p 4 (profilin) and those included in a commercial microarray of 103 allergenic components). IgE-mediated food-allergy symptoms and pollinosis were collected. Patients were skin prick tested with a plant-food and pollens panel, and specific IgE to Tri a 14 was evaluated.

RESULTS

A heterogeneous group of plant-foods was involved in local and systemic symptoms: oral allergy syndrome (75.6%), urticaria (66.7%), gastrointestinal disorders (55.6%) and anaphylaxis (75.6%), 32.4% of which were cofactor dependent (Non-Steroidal Anti-inflammatory Drugs, exercise). All tested subjects were positive to peach and Pru p 3, Tri a 14 and to some of the LTPs included in the microarray. Pollinosis was diagnosed in 75.6% of subjects, with a broad spectrum of pollen and pollen-allergen sensitization. Plane tree and mugwort were the statistically significant pollens associated with Pru p 3.

CONCLUSIONS AND CLINICAL RELEVANCE

Several plant-foods, taxonomically unrelated, independent of peach involvement, are implicated in LTP syndrome. Local symptoms should be evaluated as a risk marker for anaphylaxis because they are frequently associated with cofactor-dependent anaphylaxis. The association of these symptoms with pollinosis, especially plane tree pollinosis, could be part of this syndrome in our area.

Evaluation of the impact of sequential microwave/ultrasound processing on the IgE binding properties of Pru p 3 in treated peach juice

Peach lipid transfer protein (LTP) can cause severe allergic reactions to peach-allergic patients. It belongs to the nonspecific LTPs family, a class of proteins extremely resistant both to proteolytic digestion and to high temperatures. Food processing can either drop or increase the allergenicity, depending on the process and on the food. As far as peach-derived products (pulp, juice) are concerned, it has been previously shown how thermal treatment performed in an autoclave does not decrease LTP allergenicity. In this work, it was attempted to investigate whether sequential microwave and ultrasound processing could affect the allergenicity of peach juice. Incubation with specific anti-Pru p 3 serum showed how treating peach peel with microwave at 140 °C and with ultrasound does not eliminate Pru p 3 IgE binding properties. The application of MW/US protocol on peach pulp appeared to be insufficient for the reduction of IgE binding to Pru p 3.

Construction and analysis of a plant non-specific lipid transfer protein database (nsLTPDB)

BACKGROUND

Plant non-specific lipid transfer proteins (nsLTPs) are small and basic proteins. Recently, nsLTPs have been reported involved in many physiological functions such as mediating phospholipid transfer, participating in plant defence activity against bacterial and fungal pathogens, and enhancing cell wall extension in tobacco. However, the lipid transfer mechanism of nsLTPs is still unclear, and comprehensive information of nsLTPs is difficult to obtain.

METHODS

In this study, we identified 595 nsLTPs from 121 different species and constructed an nsLTPs database--nsLTPDB--which comprises the sequence information, structures, relevant literatures, and biological data of all plant nsLTPs http://nsltpdb.life.nthu.edu.tw/.

RESULTS

Meanwhile, bioinformatics and statistics methods were implemented to develop a classification method for nsLTPs based on the patterns of the eight highly-conserved cysteine residues, and to suggest strict Prosite-styled patterns for Type I and Type II nsLTPs. The pattern of Type I is C X2 V X5-7 C [V, L, I] × Y [L, A, V] X8-13 CC × G X12 D × [Q, K, R] X2 CXC X16-21 P X2 C X13-15C, and that of Type II is C X4 L X2 C X9-11 P [S, T] X2 CC X5 Q X2-4 C[L, F]C X2 [A, L, I] × [D, N] P X10-12 [K, R] X4-5 C X3-4 P X0-2 C. Moreover, we referred the Prosite-styled patterns to the experimental mutagenesis data that previously established by our group, and found that the residues with higher conservation played an important role in the structural stability or lipid binding ability of nsLTPs.

CONCLUSIONS

Taken together, this research has suggested potential residues that might be essential to modulate the structural and functional properties of plant nsLTPs. Finally, we proposed some biologically important sites of the nsLTPs, which are described by using a new Prosite-styled pattern that we defined.

Discovery, identification and comparative analysis of non-specific lipid transfer protein (nsLtp) family in Solanaceae

Plant non-specific lipid transfer proteins (nsLtps) have been reported to be involved in plant defense activity against bacterial and fungal pathogens. In this study, we identified 135 (122 putative and 13 previously identified) Solanaceae nsLtps, which are clustered into 8 different groups. By comparing with Boutrot’s nsLtp classification, we classified these eight groups into five types (I, II, IV, IX and X). We compared Solanaceae nsLtps with Arabidopsis and Gramineae nsLtps and found that (1) Types I, II and IV are shared by Solanaceae, Gramineae and Arabidopsis; (2) Types III, V, VI and VIII are shared by Gramineae and Arabidopsis but not detected in Solanaceae so far; (3) Type VII is only found in Gramineae whereas type IX is present only in Arabidopsis and Solanaceae; (4) Type X is a new type that accounts for 52.59% Solanaceae nsLtps in our data, and has not been reported in any other plant so far. We further built and compared the three-dimensional structures of the eight groups, and found that the major functional diversification within the nsLtp family could be predated to the monocot/dicot divergence, and many gene duplications and sequence variations had happened in the nsLtp family after the monocot/dicot divergence, especially in Solanaceae.

Skin reactions triggered by the use of cosmetic products in nonspecific lipid transfer protein-sensitive patients

Nonspecific lipid transfer proteins (nsLTPs) are members of the prolamine superfamily and they are found in pollen and food, as well as in latex. Due to the strong stability both against pepsin digestion and thermal denaturation, sensitisation towards these proteins is often associated with severe systemic reactions (angioedema, urticaria, asthma, anaphylaxis, etc.) following the ingestion of both raw or fresh food and cooked or preserved food. Many studies have shown reactivity towards nsLTPs both via inhalation and orally and in this study we present two cases of nsLTPs-sensitive patients who manifested the immediate onset of skin reactions following the use of cosmetic products containing these proteins. Thus, in order to prevent immediate reactions linked to their use, it is necessary to recommend nsLTPssensitive patients to avoid the topical use of products containing these proteins (and obviously the ingestion of foods containing these proteins).

Chronic spontaneous urticaria in children: itching for insight

While there is increasing information about the pathogenesis and treatment of chronic spontaneous urticaria (csU) in adults, there is little published information about csU in children. Consequently, most of the recommendations contained in current guidelines for the prevention and treatment of csU in infants and children is based on extrapolation of data obtained in adults. To rectify this, this review points out critical gaps in our knowledge and suggests strategies which may help us to improve our understanding of this condition. How common is csU in children? What do we know about its clinical presentation and the presence of useful biomarkers? What are its common underlying causes? What is the course of csU in children? How does csU affect the everyday life of children? What treatment options are available for children? To answer these questions, two separate types of information are required. The first is information about the prevalence of the condition in the community at large and how csU affects the everyday life of both the child-patient and the parent or carer. Because most csU cases in infants and children do not come to specialists but are treated by general practitioners or by parents using over-the-counter medications, these questions may be answered only by general population surveys or schools programmes. The second is clinical information including family history and disease presentation, the presence of biomarkers and comorbidities, objective measures of severity, frequency and duration of exacerbations, the response to therapy and the time to remission. Targeted questionnaires need to be developed and validated for these investigations. This has already begun in Germany with the establishment of the CU-KID Netzwerk (Email address: cu-kid@charite.de), the aim of which is to identify clinical centres and colleagues who treat children with urticaria and to initiate the information gathering described above.

Thaumatin-like protein and baker's respiratory allergy

BACKGROUND

Baker's asthma and rhinitis are among the most common occupational diseases. Inhaled cereal flours, such as wheat, especially cause this disease.

OBJECTIVE

To identify and test in vivo clinically important wheat allergens in baker's respiratory allergy in a Finnish population.

METHODS

Potential wheat allergens were purified using chromatographic methods from salt-soluble protein extracts of wheat flour and were used in skin prick tests with serial 10-fold dilutions (0.5-0.005 mg/mL). Twenty patients with baker's rhinitis, asthma, or both participated in this study. All the patients had positive skin prick test reactions and specific IgE antibodies to wheat flour. The control group consisted of 10 healthy individuals. Molecular identities of purified wheat allergens were characterized using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and tandem mass spectrometry.

RESULTS

Allergen concentrations of 0.3-0.5 mg/mL revealed that 12 patients reacted to a-amylase inhibitor (alpha-AI), 9 to peroxidase I (PI), 9 to thaumatin-like protein (TLP), and 6 to lipid transfer protein 2G (LTP2G). Conversely, with allergen concentrations of 0.05 mg/mL, 5 patients responded to alpha-AI, 3 to PI, 4 to LTP2G, and 6 to TLP. Of these, TLP and LTP2G are now observed to be new allergens associated with baker's asthma.

CONCLUSIONS

In addition to the earlier-described alpha-AI and PI, TLP and LTP2G are important in vivo wheat allergens in baker's allergies in Finland. Further studies are needed to elucidate the role of these novel wheat allergens in respiratory disorders.

Biochemical, immunological and clinical characterization of a cross-reactive nonspecific lipid transfer protein 1 from mulberry

BACKGROUND

Mulberry (Morus spp.) is a genus comprising several species of deciduous trees whose fruits are commonly eaten in southern Europe. Subjects with severe systemic reaction have been described. The aim of this study was to isolate the allergens of this species.

METHODS

A nonspecific lipid transfer protein 1 (ns-LTP1) was purified from black mulberry by ion exchange and reverse phase high-performance liquid chromatography, and the primary structure was elucidated by direct protein sequencing. Its allergenic activity was evaluated in vivo by skin prick test and in vitro by Western Blot, CD203c basophil activation assay and high throughput multiplex inhibition method on immunosolid-phase allergen chip (ISAC).

RESULTS

Mulberry ns-LTP (Mor n 3) comprises 91 amino acids producing a molecular mass of 9246 Da. This protein shows high sequence identity with several allergenic ns-LTP1. Immunoblot analysis and CD203c activation assay demonstrated its allergenic activity in symptomatic subjects and in ns-LTP allergic patients who are not mulberry consumers. Immunological co-recognition was studied in vivo on a selected group of well-characterized ns-LTP allergic patients showing a high percentage of nMor n 3(+) subjects (88.46%) even in patients who have never eaten mulberry before. IgE inhibition on ISAC micro-array demonstrated an almost complete cross-reactivity to nArt v 3, rCor a 8 and a very high percentage of inhibition to nPru p 3.

CONCLUSIONS

Mor n 3 is the first allergen isolated in black mulberry and immunologically characterized. It displayed allergenic activity among symptomatic and nonconsumer patients and a pattern of cross-reactivity to other plant-derived LTPs.

Nonhost resistance of barley to different fungal pathogens is associated with largely distinct, quantitative transcriptional responses

Nonhost resistance protects plants against attack by the vast majority of potential pathogens, including phytopathogenic fungi. Despite its high biological importance, the molecular architecture of nonhost resistance has remained largely unexplored. Here, we describe the transcriptional responses of one particular genotype of barley (Hordeum vulgare subsp. vulgare 'Ingrid') to three different pairs of adapted (host) and nonadapted (nonhost) isolates of fungal pathogens, which belong to the genera Blumeria (powdery mildew), Puccinia (rust), and Magnaporthe (blast). Nonhost resistance against each of these pathogens was associated with changes in transcript abundance of distinct sets of nonhost-specific genes, although general (not nonhost-associated) transcriptional responses to the different pathogens overlapped considerably. The powdery mildew- and blast-induced differences in transcript abundance between host and nonhost interactions were significantly correlated with differences between a near-isogenic pair of barley lines that carry either the Mlo wild-type allele or the mutated mlo5 allele, which mediates basal resistance to powdery mildew. Moreover, during the interactions of barley with the different host or nonhost pathogens, similar patterns of overrepresented and underrepresented functional categories of genes were found. The results suggest that nonhost resistance and basal host defense of barley are functionally related and that nonhost resistance to different fungal pathogens is associated with more robust regulation of complex but largely nonoverlapping sets of pathogen-responsive genes involved in similar metabolic or signaling pathways.

Panallergens and their impact on the allergic patient

The panallergen concept encompasses families of related proteins, which are involved in general vital processes and thus, widely distributed throughout nature. Plant panallergens share highly conserved sequence regions, structure, and function. They are responsible for many IgE cross-reactions even between unrelated pollen and plant food allergen sources. Although usually considered as minor allergens, sensitization to panallergens might be problematic as it bears the risk of developing multiple sensitizations. Clinical manifestations seem to be tightly connected with geographical and exposure factors. Future population- and disease-based screenings should provide new insights on panallergens and their contribution to disease manifestations. Such information requires molecule-based diagnostics and will be valuable for developing patient-tailored prophylactic and therapeutic approaches. In this article, we focus on profilins, non-specific lipid transfer proteins, polcalcins, and Bet v 1-related proteins and discuss possible consequences of panallergen sensitization for the allergic patient. Based on their pattern of IgE cross-reactivity, which is reflected by their distribution in the plant kingdom, we propose a novel classification of panallergens into ubiquitously spread "real panallergens" (e.g. profilins) and widespread "eurallergens" (e.g. polcalcins). "Stenallergens" display more limited distribution and cross-reactivity patterns, and "monallergens" are restricted to a single allergen source.

Analysis of protein composition of red wine in comparison with rosé and white wines by electrophoresis and high-pressure liquid chromatography-mass spectrometry (HPLC-MS)

Wine proteins not only influence wine stability but are also being discussed as potential allergens. Proteins from red, rosé, and white wines were enriched by dialysis and lyophilization followed by separation by SDS-PAGE. Significant differences were detected in the protein compositions of the analyzed wine varieties, and the major protein bands were identified by mass spectrometry after in-gel digestion with trypsin. In German Portugieser red wine, a total of 121 tryptic peptides were identified, which were attributed to 12 grape proteins and 6 proteins derived from yeast. Among the identified constituents are several proteins considered to influence wine stability and previously described potential grape allergens. The pathogenesis-related proteins represent the main proteins in all of the wines, but only some red wines show a band with a molecular mass of 12 kDa, identified as a lipid transfer protein (LTP). The occurrence and distribution of LTP depend on the wine variety.

Characteristic motifs for families of allergenic proteins

The identification of potential allergenic proteins is usually done by scanning a database of allergenic proteins and locating known allergens with a high sequence similarity. However, there is no universally accepted cut-off value for sequence similarity to indicate potential IgE cross-reactivity. Further, overall sequence similarity may be less important than discrete areas of similarity in proteins with homologous structure. To identify such areas, we first classified all allergens and their subdomains in the Structural Database of Allergenic Proteins (SDAP, http://fermi.utmb.edu/SDAP/) to their closest protein families as defined in Pfam, and identified conserved physicochemical property motifs characteristic of each group of sequences. Allergens populate only a small subset of all known Pfam families, as all allergenic proteins in SDAP could be grouped to only 130 (of 9318 total) Pfams, and 31 families contain more than four allergens. Conserved physicochemical property motifs for the aligned sequences of the most populated Pfam families were identified with the PCPMer program suite and catalogued in the webserver MotifMate (http://born.utmb.edu/motifmate/summary.php). We also determined specific motifs for allergenic members of a family that could distinguish them from non-allergenic ones. These allergen specific motifs should be most useful in database searches for potential allergens. We found that sequence motifs unique to the allergens in three families (seed storage proteins, Bet v 1, and tropomyosin) overlap with known IgE epitopes, thus providing evidence that our motif based approach can be used to assess the potential allergenicity of novel proteins.

Isolation and identification of two lipid transfer proteins in pomegranate (Punica granatum)

Lipid transfer proteins (LTPs) are a family of low molecular mass (7-9 kDa) polypeptides, the members of which share 35-95% sequence homology. These proteins are widely distributed throughout the plant kingdom and are receiving attention for their biochemical characteristics and biological activity. LTPs are indeed studied in different research fields varying from allergy to food technology, and numerous molecules belonging to this class are progressively being identified and investigated. Proteins from pomegranate juice were fractioned by cation exchange chromatography and analyzed by SDS-PAGE. Two proteins were identified as putative LTPs on the basis of their molecular weights and their electrophoretic behaviors under reducing and nonreducing conditions. Finally, proteins were purified and characterized by mass spectrometry. This analysis confirmed that the two polypeptides are LTPs on the basis of an amino acid sequence common to LTPs from other plant sources and cysteine content. The two proteins, named LTP1a and LTP1b, showed similar molecular masses but different immunological profiles when immunodetected with rabbit antibodies specific for Pru p 3 and human IgE from a patient suffering from pomegranate allergy. The demonstration of the existence of two immunologically unrelated LTPs in pomegranate confirms the variability and the complexity of the plant LTP family. This should be taken into account when the role of these proteins as elicitors of allergies to fruits is investigated and could help to explain the contradictory literature data on pomegranate allergy.

Lipid transfer proteins from Rosaceae fruits share consensus epitopes responsible for their IgE-binding cross-reactivity

Four IgE-binding epitopes have been characterized that cover a large area (40%) of the molecular surface of lipid transfer protein allergens of Rosaceae (apple, peach, apricot, and plum). They mainly correspond to electropositively charged regions protruding on the molecular surface of the modeled apple (Mal d 3), apricot (Pru ar 3), and plum (Pru d 3) allergens. Two of these epitopes consist of consensus epitopes structurally conserved among the lipid transfer protein allergens from the Rosaceae. Their occurrence in different lipid transfer protein allergens presumably accounts for the IgE-binding cross-reactivity often observed among different Rosaceae fruits. In this respect, LTP consist of phylogenetically- and structurally-related pan allergens. However, the IgE-binding cross-reactivity due to fruit lipid transfer protein has varying degrees of clinical relevance and this cross-reactivity is not necessarily accompanied by a cross-allergenicity to the corresponding fruits.

Evolutionary biology of plant food allergens

The majority of plant food allergens can be grouped into just 4 protein families. This review summarizes the evolutionary relationships of allergenic and nonallergenic members of these families. Proteins from the prolamin superfamily have been described in vascular plants. This superfamily contains several allergenic (2S albumins, nonspecific lipid transfer proteins, and cereal amylase and protease inhibitors) and nonallergenic (hybrid proline-rich proteins, cereal indolines, and alpha-globulins) member families. The cupin superfamily comprises numerous functionally highly diverse protein families from all groups of organisms. However, allergenicity within the cupins is confined to the vicilin and legumin seed storage proteins. Profilins are ubiquitous eukaryotic proteins that are nonallergenic, with the exception of profilins from flowering plants. Finally, the Bet v 1 superfamily contains the pathogenesis-related proteins 10 family, the family of major latex proteins and ripening-related proteins, the norcoclaurine synthases, and the cytokinin-binding proteins, with pathogenesis-related proteins 10 family members from certain taxa being the only allergenic members. The study of the distribution of allergenic and nonallergenic members of protein families will provide new insights into the evolution of allergenicity and the factors that make proteins allergenic.

Lipid transfer protein allergy: primary food allergy or pollen/food syndrome in some cases

PURPOSE OF REVIEW

To summarize recent findings on non-specific lipid transfer proteins in food allergy, with a specific focus on the localization, stability and route of sensitization.

RECENT FINDINGS

Plant non-specific lipid transfer proteins are major food allergens, especially in the Mediterranean area. They have been identified as allergens in a number of foods and the list grows ever longer. As non-specific lipid transfer proteins are considered to be "true" food allergens that sensitize directly via the gastrointestinal tract their stability during food processing and gastric digestion has been studied in more detail. In addition, several groups have tried to determine the sensitization patterns of lipid transfer protein-reactive patients, to determine and possibly clarify the observed geographical differences in sensitization. Different sensitization routes (via the respiratory tract or even transdermally) have been suggested.

SUMMARY

As the structure and molecular properties of non-specific lipid transfer proteins are resolved and more purified non-specific lipid transfer proteins become available for diagnostic purposes, detailed studies on the sensitization pattern and route are becoming feasible. Continuing studies on the pattern of lipid transfer protein sensitization will give more insight into the development and possible treatment of lipid transfer protein-related food allergy.

Evaluation of the IgE cross-reactions among vespid venoms. A possible approach for the choice of immunotherapy

BACKGROUND

Hymenoptera venom allergy can be effectively cured with specific immunotherapy, thus the correct identification of the allergen is essential. In the case of multiple skin and serum positivities it is important to know if a cross-reaction among venoms is present. We studied by CAP-inhibition assays the degree of cross-reactivity between Vespula vulgaris and Polistes dominulus.

METHODS

Serum samples were obtained from consecutive patients with a clinical history of grade III-IV reactions to hymenoptera sting and with nondiscriminative skin/CAP positivity to both Vespula and Polistes. Inhibition assays were carried out with a CAP method, incubating the sera separately with both venoms and subsequently measuring the specific immunoglobulin E (IgE) to venoms themselves.

RESULTS

Forty-five patients (33 male, mean age 40 years, age range 12-74, total serum IgE 242 +/- 168 kU/l) were included. Their specific IgE to Vespula and Polistes were 12.03 +/- 5.70 kU/l and 10.7 +/- 2.0 kU/l (P = NS), respectively. At the CAP-inhibition assays, in 25 patients a >75% heterologous inhibition by P. dominulus venom against V. vulgaris-specific IgE was found. In six subjects V. vulgaris venom effectively inhibited the P. dominulus-specific IgE. In the remaining 14 cases the CAP-inhibition test provided intermediate and not discriminative results.

CONCLUSION

In 31/45 patients, the double sensitizations to venoms were probably the result of cross-reactions and the CAP-inhibition allowed identifying the true double sensitizations. This approach may be helpful for the correct prescription of immunotherapy in the case of V. vulgaris and P. dominulus double positivity.

Plant non-specific lipid transfer proteins: an interface between plant defence and human allergy

Plant non-specific LTPs (lipid transfer proteins) form a protein family of basic polypeptides of 9 kDa ubiquitously distributed throughout the plant kingdom. The members of this family are located extracellularly, usually associated with plant cell walls, and possess a broad lipid-binding specificity closely related to their three-dimensional structure. The nsLTP fold is characterized by a compact domain composed of 4 alpha-helices, firmly held by a network of 4 conserved disulphide bridges. This fold presents a large internal tunnel-like cavity, which can accommodate different types of lipids. nsLTPs are involved in plant defence mechanisms against phytopathogenic bacteria and fungi, and, possibly, in the assembly of hydrophobic protective layers of surface polymers, such as cutin. In addition, several members of the nsLTP family have been identified as relevant allergens in plant foods and pollens. Their high resistance to both heat treatment and digestive proteolytic attack has been related with the induction by these allergens of severe symptoms in many patients. Therefore, they are probably primary sensitizers by the oral route. nsLTP sensitization shows an unexpected pattern throughout Europe, with a high prevalence in the Mediterranean area, but a low incidence in Northern and Central European countries.

Glycerolipid transfer for the building of membranes in plant cells

Membranes of plant organelles have specific glycerolipid compositions. Selective distribution of lipids at the levels of subcellular organelles, membrane leaflets and membrane domains reflects a complex and finely tuned lipid homeostasis. Glycerolipid neosynthesis occurs mainly in plastid envelope and endoplasmic reticulum membranes. Since most lipids are not only present in the membranes where they are synthesized, one cannot explain membrane specific lipid distribution by metabolic processes confined in each membrane compartment. In this review, we present our current understanding of glycerolipid trafficking in plant cells. We examine the potential mechanisms involved in lipid transport inside bilayers and from one membrane to another. We survey lipid transfers going through vesicular membrane flow and those dependent on lipid transfer proteins at membrane contact sites. By introducing recently described membrane lipid reorganization during phosphate deprivation and recent developments issued from mutant analyses, we detail the specific lipid transfers towards or outwards the chloroplast envelope.

Modeling the structure of the StART domains of MLN64 and StAR proteins in complex with cholesterol

Steroidogenic acute regulatory protein-related lipid transfer (StART) domains are ubiquitously involved in intracellular lipid transport and metabolism and other cell-signaling events. In this work, we use a flexible docking algorithm, comparative modeling, and molecular dynamics (MD) simulations to generate plausible three-dimensional atomic models of the StART domains of human metastatic lymph node 64 (MLN64) and steroidogenic acute regulatory protein (StAR) proteins in complex with cholesterol. Our results show that cholesterol can adopt a similar conformation in the binding cavity in both cases and that the main contribution to the protein-ligand interaction energy derives from hydrophobic contacts. However, hydrogen-bonding and water-mediated interactions appear to be important in the fine-tuning of the binding affinity and the position of the ligand. To gain insights into the mechanism of binding, we carried out steered MD simulations in which cholesterol was gradually extracted from within the StAR model. These simulations indicate that a transient opening of loop Omega1 may be sufficient for uptake and release, and they also reveal a pathway of intermediate states involving residues known to be crucial for StAR activity. Based on these observations, we suggest specific mutagenesis targets for binding studies of cholesterol and its derivatives that could improve our understanding of the structural determinants for ligand binding by sterol carrier proteins.

Computer prediction of allergen proteins from sequence-derived protein structural and physicochemical properties

BACKGROUND

Computational methods have been developed for predicting allergen proteins from sequence segments that show identity, homology, or motif match to a known allergen. These methods achieve good prediction accuracies, but are less effective for novel proteins with no similarity to any known allergen.

METHODS

This work tests the feasibility of using a statistical learning method, support vector machines, as such a method. The prediction system is trained and tested by using 1005 allergen proteins from the Allergome database and 22,469 non-allergen proteins from 7871 Pfam families.

RESULTS

Testing results by an independent set of 229 allergen and 6717 non-allergen proteins from 7871 Pfam families show that 93.0% and 99.9% of these are correctly predicted, which are comparable to the best results of other methods. Of the 18 novel allergen proteins non-homologous to any other proteins in the Swissprot database, 88.9% is correctly predicted. A further screening of 168,128 proteins in the Swissprot database finds that 2.9% of the proteins are predicted as allergen proteins, which is consistent with the estimated numbers from motif-based methods.

CONCLUSIONS

Our study suggests that SVM is a potentially useful method for predicting allergen proteins and it has certain capability for predicting novel allergen proteins. Our software can be accessed at .

Cross-reactivity of pollen allergens: recommendations for immunotherapy vaccines

PURPOSE OF REVIEW

This review will summarize recent research on pollen allergen and epitope cross-reactivity. Knowledge of these relationships aids in the rational formulation of allergen immunotherapy vaccines.

RECENT FINDINGS

There has been further clarification of panallergens and their roles as both major and minor allergens. Recent studies have targeted non-specific lipid transfer proteins and calcium-binding proteins (polcalcins), as well as pathogenesis-related protein families and profilins. Polcalcins and non-specific lipid transfer proteins are responsible for pollen-fruit interactions as well as pollen cross-reactivity, in some cases, but not all, accounting for major allergenicity. Delineation of the enzymatic activity of certain allergens explains the ubiquitous nature of these pollen proteins.

SUMMARY

Characterization of specific pollen allergens and their protein families has provided insight into the grounds for cross-reactivity. Continuing clarification of these relationships will allow the substitution and consolidation of inhalant extracts as described in the conclusion.