**1. Introduction**

Legumes are dicotyledon plants in the order Fabales and the family Fabacea. They produce fruit contained in pods and filled with seeds. In this chapter, we discuss three species of legumes in the genus *Lupinus* (*Lupinus albus*, *L. angustiflora*, and *Lupinus luteus*) and the most common allergenic species of the family Papilionaceae, including soja *Glycine max*; *Arachis hypogaea*, *A. duraensis*, and *A. ipaensis*; lentil (*Lens culinaris*); pea (*Pisum sativum*); and chickpea (*Cicer arietinum*).

A food allergy is an immune system reaction that occurs after eating certain types of food. Symptoms are variable and can be caused even by small amounts of allergenic proteins, leading to hives, swollen airways, and digestive problems. Food allergies are a growing concern worldwide. This increase is suspected to be related with industrial production, pollution, additives, and consumption of trash food [1]. There are reports of children of East Asian or African ethnicity in Western nations having an increased risk of developing food allergies compared with Caucasian children. This suggests that adopting Westernized food habits could increase food allergies in African or Asian countries [2, 3].

The research about healthy, low-cost alternative products that can meet the enormous demands of a growing population involve legumes [4]. Legume crops represent a sustainability solution, serving as a fundamental source of high-quality alternative protein, reducing the emission of greenhouse gases, allowing the sequestration of carbon in soils, saving the CO2 print thanks to the nitrogen fertilizer, it free highquality organic matter that facilitate water retention and perform the soil nutrients circulation among others uses [5]. Despite their advantages, legumes contain proteins that can potentially cause food allergies. Several allergens from different legumes have been identified and characterized as proteins with potential allergic effects. These include lentil, pea, chickpea, soy, peanut, and lupine [6].

Clinically, the absence of sensibilization phase is a reliable indicator of the tolerance to an allergen. In this context, the presence of sensitization to a specific allergen protein has to be proven [7] both, the specific reactivity to a particular allergen protein and the cross-reactivity to other related allergens. The most frequent crossreactivity process described clinically is that between lupin and peanut [8].

In Spain, consumption of legumes is common because they are an important part of the Mediterranean diet. It is estimated that consumption of legumes in Spain is 4.8 kg per year, with a greater percentage of children eating them as compared to adults. Legume consumption in Spain is greater in girls than in boys [9]. One study in Spain showed that food allergies were detected in 20.8% of children and 14% of adults. In the overall Spanish population, legumes were responsible of the 14.3% of the food allergies [10]. Another study of Spain's pediatric population found that 10% of children suffered from food allergies caused by lentil and 6.7% of children suffered from food allergies caused by peanuts. Lentil was found to be the most allergenic, causing 78% of reactions, followed by chickpea (72%) and peanut (33%) [9].

In Europe, legumes are the fifth-leading cause of food allergies [11]. A metaanalysis of studies conducted in Europe between January 2000 and September 2012 found that the percentage of the population with symptoms of food allergies plus specific immunoglobulin E (IgE) positivity activation to at least one food allergen was 3%–4.6% in children and 2.2%–2.66% in adults [12]. The same study concluded that the frequency of food allergy is greatest in northwestern European countries compared to southern European countries, which had the lowest prevalence. Some factors related to food allergies include environmental, genetic, and epigenetic factors that could suggest differences between global populations [13].

The general prevalence of food allergies is not clearly defined due to the lack of reliable data and the highly variable allergy patterns in different parts of the world. A selection of mixed developed country data (Allergy, Asthma & Immunology Research *Comparative Analysis of Molecular Allergy Features of Seed Proteins from Soybean… DOI: http://dx.doi.org/10.5772/intechopen.106971*

2018) found that some allergies, like those to peanut, demonstrate heritability in Caucasian populations; skin immune responses shows differences between Asians and Caucasians. These types of studies have not yet been conducted in non-White populations, however, there exists some interest data showing that Black South African children present a significantly lower prevalence of peanut allergy compared to children of mixed-race origin (Black and Caucasian) by unknown factors [13].

One interesting fact about cross-reactivity is that it could be caused by proteins that come from species that are taxonomically distant. Examples of these antigens are panallergens, which are proteins conserved by evolution due to their important defense, structural, and storage functions [7]. If a person has an allergy to cow milk proteins, they are also probably allergic to goat milk proteins [14]. In the case of legumes, cross-reactivity to more than one legume is often found in children [9].

Overall, allergic features of allergen proteins could be attenuated by thermic proteolytic denaturalization due to the modification of the quaternary protein structure where superficial epitopes of these proteins' antigenic regions can still develop some allergenicity reactions. Despite this, there are studies that also show resistance to thermic, chemical, and proteolytic denaturalization, with is a common characteristic in legumes [15]. Some examples of resistance to denaturalization include allergen proteins like Cupins, very stable storage proteins that include legumins (11 S) and vicilins (7 S), both containing two common β-barrel structures in their globular domain. These appear to be a relevant stable structural motif, confirming resistance to denaturation and proteolysis [16]. Lipid transfer proteins (LTPs) have resistance to pepsin and to chemical digestion [17]; PR-proteins have thermostable structure [10] allowing them staying unalterable at physiological temperature. This stability plays an important role in allowing allergen active protein fragments to pass to the gastrointestinal tract, causing a food allergy.

There is a large public database of allergenic legume proteins with several isoforms. The commonly shared partial epitopes and their conservation in the same family of proteins in different species could be helpful in designing possible strategies to prevent cross-reactivity.

The aim of this work is to carry out an exhaustive molecular and structural analysis of the most common allergenic legume proteins through bioinformatic approaches.

### **2. Materials and methods**

#### **2.1 Search of legume proteins sequences**

We used the Allergome and UniProt databases to search for allergenic legume proteins for this study. The proteins chosen are characterized by having complete sequences and being in mature form. The search was carried out on the available species of lentil, pea, chickpea, soybean, and lupine (**Table 1A-E**).

#### **2.2 Alignment of sequences**

The complete and mature sequences of lentil (*Len c 3*, *Len c 3.0101*, and *Len c aglutinin*), chickpea (*Cic a 1, Cic a 3, Cic a 4, Cic a 6*), pea (*Pis s 2* (7 s vicilin), *Pis s 3* (LTP), *Pis s 3.0101*(LTP), *Pis s 6* (PR-protein, Pis S aglutin, Pis s albumin)), lupine (*Lup a 1, Lup a alpha conglutin, Lup a delta conglutin, Lup a gamma conglutin, Lup a 4, Lup an 1, Lup an 1.0101, Lup an 3, Lup an 3.0101, Lup an alpha conglutin, Lup an delta*


*Comparative Analysis of Molecular Allergy Features of Seed Proteins from Soybean… DOI: http://dx.doi.org/10.5772/intechopen.106971*


*Table includes the species name, the common name of the allergen, the type of protein according to its biological nature/function, and the UniProt entry name (UniProtKB). All sequences were used for alignment,T-cell epitope search, and IgE analysis. Sequences from all lupin and soybean species were used for the post-translational modification search tasks (A and B). For secondary and tertiary structure assessment, only the sequences of interest were used:* G. max *(Gly m 5, Gly m 5.0301, Gly m 8, and Gly m 8.0101);* L. albus *(Lup a 1 and Lup a alpha conglutin);* Lupinus angustifolius *(Lup an alpha e);* P. sativum *(Pis s albumin);* C. arietinum *(Cic a 6); and* A. hypogaea *(Ara h 5.0101).*

#### **Table 1.**

*Summary of the sequences used in successive studies.*

*conglutin, Lup an gamma conglutin, Lup l 4*), and peanut (*Ara d 2, Ara d 6, Ara h 1, Ara h 1.0101, Ara h 2, Ara h 2.0101, Ara h 2.0201, Ara h 2.0202, Ara h 3, Ara h 3.0201, Ara h agglutin, Ara h 5, Ara h 5.0101, Ara h 6, Ara h 6.0101, Ara h 7.0101, Ara h 7.0102, Ara h 7.0301, Ara h 8, Ara h 8.0101, Ara h 8.0201, Ara h 9.0101, Ara h 10.0101, Ara h 11.0101, Ara h 11.0102, Ara h 13.0102, Ara h 14.0101, Ara h 14.0102, Ara h 14.0103, Ara h 15.0101, Ara h 16, Ara h 17)* were aligned by pairs against soybean allergens (*Gly m 5, Gly m 5.0301, Gly m 8, Gly m 8.0101*) extracting the identity percentage and comparing the possible differences in the amino acid nature of the protein sequences (positive charge, negative charge, and polarity) of the allergens listed above.
