Among a variety of molecular factors of the plant innate immune system, small proteins that transfer lipids and exhibit a broad spectrum of biological activities are of particular interest. These are lipid transfer proteins (LTPs). LTPs are interesting to researchers for three main features. The first feature is the ability of plant LTPs to bind and transfer lipids, whereby these proteins got their name and were combined into one class. The second feature is that LTPs are defense proteins that are components of plant innate immunity. The third feature is that LTPs constitute one of the most clinically important classes of plant allergens. In this review, we summarize the available data on the plant LTP structure, biological properties, diversity of functions, mechanisms of action, and practical applications, emphasizing their role in plant physiology and their significance in human life.

BackgroundPlant 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.ResultsThree 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 13C,15N-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 Å3). The minor conformer probably corresponds to the protein with the partially collapsed internal cavity.ConclusionsFor 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0792-6) contains supplementary material, which is available to authorized users.

Pathogenesis-related (PR) proteins are components of innate immunity system in plants. They play an important role in plant defense against pathogens. Lipid transfer proteins (LTPs) and Bet v 1 homologs comprise of two separate families of PR-proteins. Both LTPs (PR-14) and Bet v 1 homologs (PR-10) are multifunctional small proteins involving in plant response to abiotic and biotic stress conditions. The representatives of these PR-protein families do not show any sequence similarity but have other common biochemical features such as low molecular masses, the presence of hydrophobic cavities, ligand binding properties, and antimicrobial activities. Besides, many members of PR-10 and PR-14 families are ubiquitous plant panallergens which are able to cause sensitization of human immune system and crossreactive allergic reactions to plant food and pollen. This review is aimed at comparative analysis of structure-functional and allergenic properties of the PR-10 and PR-14 families, as well as prospects for their medicinal application.

No abstract

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.

Lipid transfer proteins (LTPs) participate in many important physiological processes in plants, including adaptation to stressors, e.g., salinity. Here we address the mechanism of this protective action of LTPs by studying the interaction between LTPs and abscisic acid (ABA, a “stress” hormone) and their mutual participation in suberin deposition in root endodermis of salt-stressed pea plants. Using immunohistochemistry we show for the first time NaCl induced accumulation of LTPs and ABA in the cell walls of phloem paralleled by suberin deposition in the endoderm region of pea roots. Unlike LTPs which were found localized around phloem cells, ABA was also present within phloem cells. In addition, ABA treatment resulted in both LTP and ABA accumulation in phloem cells and promoted root suberization. These results suggested the importance of NaCl-induced accumulation of ABA in increasing the abundance of LTPs and of suberin. Using molecular modeling and fluorescence spectroscopy we confirmed the ability of different plant LTPs, including pea Ps-LTP1, to bind ABA. We therefore hypothesize an involvement of plant LTPs in ABA transport (unloading from phloem) as part of the salinity adaptation mechanism.

The recombinant isoforms Lc-LTP1 and Lc-LTP3 of the lentil lipid transfer protein were overexpressed in E. coli cells. It was confirmed that both proteins are stabilized by four disulfide bonds and characterized by a high proportion of the α-helical structure. It was found that Lc-LTP1 and Lc-LTP3 possess antimicrobial activity and can bind fatty acids. Both isoforms have the ability to bind specific IgE from sera of patients with food allergies, which recognize similar epitopes of the major peach allergen Pru p 3. Both isoforms were shown to have immunological properties similar to those of other plant allergenic LTPs, but Lc-LTP3 displayed a less pronounced immunoreactivity.

The soybean allergen Gly m 4 is known to cause severe allergic reactions including anaphylaxis, unlike other Bet v 1 homologues, which induce mainly local allergic reactions. In the present study, we aimed to investigate whether the food Bet v 1 homologue Gly m 4 can be a sensitizer of the immune system. Susceptibility to gastrointestinal digestion was assessed in vitro. Transport through intestinal epithelium was estimated using the Caco-2 monolayer. Cytokine response of different immunocompetent cells was evaluated by using Caco-2/Immune cells co-culture model. Absolute levels of 48 cytokines were measured by multiplex xMAP technology. It was shown that Gly m 4 can cross the epithelial barrier with a moderate rate and then induce production of IL-4 by mature dendritic cells in vitro. Although Gly m 4 was shown to be susceptible to gastrointestinal enzymes, some of its proteolytic fragments can selectively cross the epithelial barrier and induce production of Th2-polarizing IL-5, IL-10, and IL-13, which may point at the presence of the T-cell epitope among the crossed fragments. Our current data indicate that Gly m 4 can potentially be a sensitizer of the immune system, and intercommunication between immunocompetent and epithelial cells may play a key role in the sensitization process.