Purification and primary structure of novel lipid transfer proteins from germinated lentil (Lens culinaris) seeds

Legume Allergens Pea, Chickpea, Lentil, Lupine and Beyond

PURPOSE OF THE REVIEW

In the last decade, an increasing trend towards a supposedly healthier vegan diet could be observed. However, recently, more cases of allergic reactions to plants and plant-based products such as meat-substitution products, which are often prepared with legumes, were reported. Here, we provide the current knowledge on legume allergen sources and the respective single allergens. We answer the question of which legumes beside the well-known food allergen sources peanut and soybean should be considered for diagnostic and therapeutic measures.

RECENT FINDINGS

These "non-priority" legumes, including beans, pea, lentils, chickpea, lupine, cowpea, pigeon pea, and fenugreek, are potentially new important allergen sources, causing mild-to-severe allergic reactions. Severe reactions have been described particularly for peas and lupine. An interesting aspect is the connection between anaphylactic reactions and exercise (food-dependent exercise-induced anaphylaxis), which has only recently been highlighted for legumes such as soybean, lentils and chickpea. Most allergic reactions derive from IgE cross-reactions to homologous proteins, for example between peanut and lupine, which is of particular importance for peanut-allergic individuals ignorant to these cross-reactions. From our findings we conclude that there is a need for large-scale studies that are geographically distinctive because most studies are case reports, and geographic differences of allergic diseases towards these legumes have already been discovered for well-known "Big 9" allergen sources such as peanut and soybean. Furthermore, the review illustrates the need for a better molecular diagnostic for these emerging non-priority allergen sources to evaluate IgE cross-reactivities to known allergens and identify true allergic reactions.

Leguminosas como causa infrecuente de alergia alimentaria en Colombia: reporte de dos casos y revisión de la literatura

La alergia alimentaria se ha venido incrementando a nivel mundial, afectando alrededor del 1,5 % a 2,5 % de los adultos y 6 % de los niños, y tiene un gran impacto en la calidad de vida de los pacientes y sus cuidadores, debido a las dietas de restricción. Los alérgenos más prevalentes son la leche, el huevo, el trigo, la soja, los frutos secos, el maní, el pescado y los mariscos. Las leguminosas mejor estudiadas son el maní y la soja; otras leguminosas como las lentejas, garbanzos y arvejas representan la quinta causa de alergia alimentaria en el área mediterránea, en Turquía y en la India, siendo menos prevalentes en otras áreas geográficas. La alergia a las leguminosas es una entidad infrecuente en Colombia, se desconoce la prevalencia en el país. Describimos los primeros dos casos de anafilaxia por lentejas reportados en el país. Ambos pacientes menores de 18 años, con reacciones adversas tras la ingesta de leguminosas, en las cuales se demuestra alergia mediada por IgE a las lentejas y además sensibilización en el primer caso a las arvejas y garbanzos, y en el segundo caso a los frijoles. Diferentes datos sobre la prevalencia se han descrito en varias áreas geográficas, siendo mayor en países con dietas mediterráneas. Las reacciones mediadas por IgE suelen aparecer incluso con el alimento altamente cocido, debido a la termo-estabilidad de las proteínas. La reactividad cruzada más frecuente se relaciona con los garbanzos y las arvejas.

Impact of Different Lipid Ligands on the Stability and IgE-Binding Capacity of the Lentil Allergen Len c 3

Previously, we isolated the lentil allergen Len c 3, belonging to the class of lipid transfer proteins, cross-reacting with the major peach allergen Pru p 3 and binding lipid ligands. In this work, the allergenic capacity of Len c 3 and effects of different lipid ligands on the protein stability and IgE-binding capacity were investigated. Impacts of pH and heat treating on ligand binding with Len c 3 were also studied. It was shown that the recombinant Len c 3 (rLen c 3) IgE-binding capacity is sensitive to heating and simulating of gastroduodenal digestion. While being heated or digested, the protein showed a considerably lower capacity to bind specific IgE in sera of allergic patients. The presence of lipid ligands increased the thermostability and resistance of rLen c 3 to digestion, but the level of these effects was dependent upon the ligand's nature. The anionic lysolipid LPPG showed the most pronounced protective effect which correlated well with experimental data on ligand binding. Thus, the Len c 3 stability and allergenic capacity can be retained in the conditions of food heat cooking and gastroduodenal digestion due to the presence of certain lipid ligands.

Polyphenol-Rich Lentils and Their Health Promoting Effects

Polyphenols are a group of plant metabolites with potent antioxidant properties, which protect against various chronic diseases induced by oxidative stress. Evidence showed that dietary polyphenols have emerged as one of the prominent scientific interests due to their role in the prevention of degenerative diseases in humans. Possible health beneficial effects of polyphenols are measured based on the human consumption and their bioavailability. Lentil (Lens culinaris; Family: Fabaceae) is a great source of polyphenol compounds with various health-promoting properties. Polyphenol-rich lentils have a potential effect on human health, possessing properties such as antioxidant, antidiabetic, anti-obesity, anti-hyperlipidemic, anti-inflammatory and anticancer. Based on the explorative study, the current comprehensive review aims to give up-to-date information on nutritive compositions, bioactive compounds and the health-promoting effect of polyphenol-rich lentils, which explores their therapeutic values for future clinical studies. All data of in vitro, in vivo and clinical studies of lentils and their impact on human health were collected from a library database and electronic search (Science Direct, PubMed and Google Scholar). Health-promoting information was gathered and orchestrated in the suitable place in the review.

Lipid transfer proteins: classification, nomenclature, structure, and function

The non-specific lipid transfer proteins (LTPs) constitute a large protein family found in all land plants. They are small proteins characterized by a tunnel-like hydrophobic cavity, which makes them suitable for binding and transporting various lipids. The LTPs are abundantly expressed in most tissues. In general, they are synthesized with an N-terminal signal peptide that localizes the protein to spaces exterior to the plasma membrane. The in vivo functions of LTPs are still disputed, although evidence has accumulated for a role in the synthesis of lipid barrier polymers, such as cuticular waxes, suberin, and sporopollenin. There are also reports suggesting that LTPs are involved in signaling during pathogen attacks. LTPs are considered as key proteins for the plant's survival and colonization of land. In this review, we aim to present an overview of the current status of LTP research and also to discuss potential future applications of these proteins. We update the knowledge on 3D structures and lipid binding and review the most recent data from functional investigations, such as from knockout or overexpressing experiments. We also propose and argument for a novel system for the classification and naming of the LTPs.

A novel lipid transfer protein from the pea Pisum sativum: isolation, recombinant expression, solution structure, antifungal activity, lipid binding, and allergenic properties

BACKGROUND

Plant lipid transfer proteins (LTPs) assemble a family of small (7-9 kDa) ubiquitous cationic proteins with an ability to bind and transport lipids as well as participate in various physiological processes including defense against phytopathogens. They also form one of the most clinically relevant classes of plant allergens. Nothing is known to date about correlation between lipid-binding and IgE-binding properties of LTPs. The garden pea Pisum sativum is widely consumed crop and important allergenic specie of the legume family. This work is aimed at isolation of a novel LTP from pea seeds and characterization of its structural, functional, and allergenic properties.

RESULTS

Three novel lipid transfer proteins, designated as Ps-LTP1-3, were found in the garden pea Pisum sativum, their cDNA sequences were determined, and mRNA expression levels of all the three proteins were measured at different pea organs. Ps-LTP1 was isolated for the first time from the pea seeds, and its complete amino acid sequence was determined. The protein exhibits antifungal activity and is a membrane-active compound that causes a leakage from artificial liposomes. The protein binds various lipids including bioactive jasmonic acid. Spatial structure of the recombinant uniformly (13)C,(15)N-labelled Ps-LTP1 was solved by heteronuclear NMR spectroscopy. In solution the unliganded protein represents the mixture of two conformers (relative populations ~ 85:15) which are interconnected by exchange process with characteristic time ~ 100 ms. Hydrophobic residues of major conformer form a relatively large internal tunnel-like lipid-binding cavity (van der Waals volume comes up to ~1000 Å(3)). The minor conformer probably corresponds to the protein with the partially collapsed internal cavity.

CONCLUSIONS

For the first time conformational heterogeneity in solution was shown for an unliganded plant lipid transfer protein. Heat denaturation profile and simulated gastrointestinal digestion assay showed that Ps-LTP1 displayed a high thermal and digestive proteolytic resistance proper for food allergens. The reported structural and immunological findings seem to describe Ps-LTP1 as potential cross-reactive allergen in LTP-sensitized patients, mostly Pru p 3(+) ones. Similarly to allergenic LTPs the potential IgE-binding epitope of Ps-LTP1 is located near the proposed entrance into internal cavity and could be involved in lipid-binding.

A novel lipid transfer protein from the dill Anethum graveolens L.: isolation, structure, heterologous expression, and functional characteristics

A novel lipid transfer protein, designated as Ag-LTP, was isolated from aerial parts of the dill Anethum graveolens L. Structural, antimicrobial, and lipid binding properties of the protein were studied. Complete amino acid sequence of Ag-LTP was determined. The protein has molecular mass of 9524.4 Da, consists of 93 amino acid residues including eight cysteines forming four disulfide bonds. The recombinant Ag-LTP was overexpressed in Escherichia coli and purified. NMR investigation shows that the Ag-LTP spatial structure contains four α-helices, forming the internal hydrophobic cavity, and a long C-terminal tail. The measured volume of the Ag-LTP hydrophobic cavity is equal to ~800 A(3), which is much larger than those of other plant LTP1s. Ag-LTP has weak antifungal activity and unpronounced lipid binding specificity but effectively binds plant hormone jasmonic acid. Our results afford further molecular insight into biological functions of LTP in plants.

Recombinant production and solution structure of lipid transfer protein from lentil Lens culinaris

Lipid transfer protein, designated as Lc-LTP2, was isolated from seeds of the lentil Lens culinaris. The protein has molecular mass 9282.7Da, consists of 93 amino acid residues including 8 cysteines forming 4 disulfide bonds. Lc-LTP2 and its stable isotope labeled analogues were overexpressed in Escherichia coli and purified. Antimicrobial activity of the recombinant protein was examined, and its spatial structure was studied by NMR spectroscopy. The polypeptide chain of Lc-LTP2 forms four α-helices (Cys4-Leu18, Pro26-Ala37, Thr42-Ala56, Thr64-Lys73) and a long C-terminal tail without regular secondary structure. Side chains of the hydrophobic residues form a relatively large internal tunnel-like lipid-binding cavity (van der Waals volume comes up to ∼600Å(3)). The side-chains of Arg45, Pro79, and Tyr80 are located near an assumed mouth of the cavity. Titration with dimyristoyl phosphatidylglycerol (DMPG) revealed formation of the Lc-LTP2/lipid non-covalent complex accompanied by rearrangements in the protein spatial structure and expansion of the internal cavity. The resultant Lc-LTP2/DMPG complex demonstrates limited lifetime and dissociates within tens of hours.

Lentil (Lens culinaris) lipid transfer protein Len c 3: a novel legume allergen

BACKGROUND

Lentils are increasingly consumed in many parts of the world.Two allergens, Len c 1 and 2, have been reported previously. Recently, peanut and green bean lipid transfer proteins (LTPs) have been identified as the first two members of an important group of allergens that might be associated with severe food allergies.

OBJECTIVE

To investigate lentil LTP as a potential new allergen.

METHODS

Efficacy of LTP extraction was monitored at different acidic pH values, using immunoblotting with cross-reactive anti-peach LTP antiserum. Natural LTP was purified from lentil extract and expressed as recombinant allergen in Escherichia coli. Sera from 10 lentil-allergic and/or -sensitized patients (Spain: 6, Italy: 1 and the Netherlands: 3) were used to further characterize lentil LTP.

RESULTS

Natural lentil LTP, purified from the homogenized germinated seeds and optimally extracted at pH 3, was identified and designated as allergen Len c 3. By CAP, 9/10 sera showed specific IgE to Len c 3. Recombinant (r) Len c 3 was successfully purified. The natural (n) Len c 3 CAP was completely inhibited by rLen c 3/rPru p 3. IgE binding to lentil pH 3 extract blot was completely inhibited by rLen c 3.

CONCLUSION

The availability of immunochemically active nLen/rLen c 3 as a novel legume allergen facilitates further development and implementation of a third (next to peanut and green bean) legume LTP in component-resolved diagnosis strategies and contributes to evaluate the clinical importance of legume LTPs. Preferential extraction of Len c 3 (pH 3) will affect the production of sensitive extract-based diagnostic tests.

Isolation, purification and characterization of a nonspecific lipid transfer protein from Cuminum cyminum

Cuminum cyminum, an aromatic plant from the family Umbelliferae, is used as a flavoring and seasoning agent in foods. This communication reports the characterization of a nonspecific lipid transfer protein nsLTP1 from its seeds. Plant nsLTPs are small basic proteins involved in transport of lipids between membranes. These proteins are known to participate in plant defense; however, the exact mechanism of their antimicrobial action against fungi or bacteria is still unclear. The cumin nsLTP1 has been purified using a combination of chromatographic procedures and further characterized using mass spectrometry, circular dichroism spectroscopy and Edman degradation. Amino acid sequence has been used to predict homology model of cumin nsLTP1 in complex with myristic acid, and lyso-myristoyl phosphatidyl choline (LMPC). Cumin nsLTP1 is a monomeric protein with a molecular weight of 9.7 kDa as estimated by SDS-PAGE and ESIMS. The protein shows an isoelectric point of 7.8 on 6% PAGE. The primary structure consists of 92 amino acids with eight conserved cysteine residues. The global fold of cumin nsLTP1 includes four alpha-helices stabilized by four disulfide bonds and a C-terminal tail. The role of internal hydrophobic cavity of the protein in lipid transfer is discussed.