Storage proteins

(Seed) storage proteins are proteins (albumins and globulins) of an organism that ensure the nutritive supply of the seedling during germination. This special biochemical function explains many of the properties of this group of proteins. Storage proteins are of great economic importance. They are important proteins in the animal feed of many domestic animals and also enter human nutrition via the food chain. Furthermore, storage proteins in the various seed products also represent important direct food for humans. They are resistant to heat and usually also to digestion, and their direct and cross-reactive allergenicity is of great medical-allergological importance for humans. Often even the smallest amounts are sufficient to trigger an allergic reaction.

In medical terminology, iron storage proteins such as ferritin are also called storage proteins.

They're gonna be different. families of the storage proteins are distinguished:

• 11S-Globulins (so-called Legumines)
• 7S-Globulins (Vicilins)
• 2S-Albumine

Seeds contain between 10% (cereals) and 40% of protein in dry matter. This is the reason why some patients may be allergic to small amounts of seed components, e.g. peanut products.

The storage proteins are collected by the adult plant either in vacuoles or freely in the cytosol of the nutrient tissue cells as insoluble crystals. At the same time, moisture is withdrawn from the nutritive tissue. The storage proteins therefore only become biologically active again after moistening (seeds germinate in a moist environment).

Plant storage proteins are similar protein mixtures. The main part is made up of members of 3 protein families: 2 S-albumines as well as 7S and 11S-globulins. They are the main or major allergens of seeds and are responsible for the majority of allergies to nuts or nuts and pulses (but not to cereals) and are therefore of great allergological significance.

In allergological diagnostics with total extracts, serological cross-reactivity between the various allergens is required. Serological cross-reactivity between different legumes and between legumes, nuts and seeds is frequent. This makes the clinical statement regarding the specificity of the cross-reactions more difficult. The greatest discrepancy between serological and clinical cross-reactivity is between peanut and soya allergy. Remarkable is the observation that cross-reactivities across protein families were also found. This is due to the fact that the IgE antibodies are also able to bind to unstructured loops of the protein body that protrude on the surface of the protein. An example of cross-reactivity across families is that of the 7S globulins Ara h 2(peanut) and Jug r 2(walnut) with the alpha-conglutin (11S globulin) from lupine.

A classification of plant storage proteins, which was already made in the 19th century, results from their solubility in salt-free or salty water: albumins and globulins dissolve well, prolamins only in 60-80 % ethanol and glutelins only in acid. For many storage proteins, names have become commonplace, e.g. in the peanut: Conglutin, Conarachin, Arachin for the 2S-albumin, the 7S- and 11S-globulin; beta-conglycinin and Glycinin for the 7S- and 11S-globulin from soy beans. Such terms, by their very nature, make the overview considerably more difficult.

1. Cabanillas B et al (2015) Allergic Reactions to Pine Nut: A Review. J Investig Allergol Clin Immunol 25:329-333. review.
2. Garcia-Blanca A et al (2015) Influence of age on IgE response in peanut-allergic children and adolescents from the Mediterranean area. Pediatric Allergy Immunol 26:497-502.
3. Nilsson C et al (2015) Recognition pattern of kiwi seed storage proteins in kiwifruit-allergic children. Pediatric Allergy Immunol 26:817-820.
4. Pedrosa M et al (2015) Utility of specific IgE to Ara h 6 in peanut allergy diagnosis. Ann Allergy Asthma Immunol. 115:108-112.
5. Radauer C et al (2015) Stable plant food allergens II: Storage proteins. In: Kleine-Tebbe J et al. eds. molecular allergy diagnostics. Springer Publishing House Berlin-Heidelberg S 61-72