Limits...
2S Albumin Storage Proteins: What Makes them Food Allergens?

Moreno FJ, Clemente A - Open Biochem J (2008)

Bottom Line: This review describes the main biochemical, structural and functional properties of these proteins thought to play a role in determining their potential allergenicity. 2S albumins are considered to sensitize directly via the gastrointestinal tract (GIT).The flexible and solvent-exposed hypervariable region of these proteins is immunodominant and has the ability to bind IgE from allergic patients sera.Finally, the interaction of these proteins with other components of the food matrix might influence the absorption rates of immunologically reactive 2S albumins but also in their immune response.

View Article: PubMed Central - PubMed

Affiliation: Instituto de Fermentaciones Industriales (CSIC), C/ Juan de la Cierva 3, 28006 Madrid, Spain.

ABSTRACT
2S albumin storage proteins are becoming of increasing interest in nutritional and clinical studies as they have been reported as major food allergens in seeds of many mono- and di-cotyledonous plants. This review describes the main biochemical, structural and functional properties of these proteins thought to play a role in determining their potential allergenicity. 2S albumins are considered to sensitize directly via the gastrointestinal tract (GIT). The high stability of their intrinsic protein structure, dominated by a well-conserved skeleton of cysteine residues, to the harsh conditions present in the GIT suggests that these proteins are able to cross the gut mucosal barrier to sensitize the mucosal immune system and/or elicit an allergic response. The flexible and solvent-exposed hypervariable region of these proteins is immunodominant and has the ability to bind IgE from allergic patients sera. Several linear IgE-binding epitopes of 2S albumins spanning this region have been described to play a major role in allergenicity; the role of conformational epitopes of these proteins in food allergy is far from being understood and need to be investigated. Finally, the interaction of these proteins with other components of the food matrix might influence the absorption rates of immunologically reactive 2S albumins but also in their immune response.

No MeSH data available.


Related in: MedlinePlus

Schematic representation of the disulphide bond patterns formed between the eight conserved cysteine residues in the 2S albumin family.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2570561&req=5

Figure 1: Schematic representation of the disulphide bond patterns formed between the eight conserved cysteine residues in the 2S albumin family.

Mentions: tions, mainly derived from proteolytic processing; these isoforms may show considerable differences in their structures and biological properties. Nevertheless, it is possible to define the protein structure of a “typical” 2S albumin. These proteins are synthesized as a single larger precursor polypeptide of Mr~18-21 kD, which is co-translationally transported into the lumen of the endoplasmic reticulum. After the formation of four intra-chain disulphide bonds, involving eight conserved cysteine residues, the folded protein is transported into the vacuole where is subsequently processed to a polypeptide of Mr ~12-14 kD and eventually to the large and small subunits of Mr~8-10 and 3-4 kD, respectively [14]. Owing to the conserved skeleton of cysteine residues, the small and large subunits remain associated by two inter-molecular disulphide bonds in the mature form; other two intra-chain disulphide bonds are present within the large subunit. Fig. (1) depicts the typical disulphide bond mapping of the 2S albumins. The conserved scaffold includes that the third and fourth cysteine residues are consecutive in the polypeptide chain (large subunit) and the fifth and sixth cysteine residues are separated by only one residue. The inter-chain disulphide bonds are those formed between cysteine residues 1-5 and 2-3 whereas the intra-chain bridges are formed by the cysteine residues 4-7 and 6-8. A range of variants differing from the “typical” 2S albumins in their structure or mode of biosynthesis has been reported. Such is the case of the major methionine-rich albumin, SFA8, from sunflower (Helianthus annuus) in which post-translational processing seems to be limited to the removal of the signal peptide and the pro-region with no further proteolytic cleavage of the polypeptide chain into large and small subunits [15]. SFA8 is the only 2S albumin isolated and characterized to date that is composed of a single polypeptide chain [16]. Variation in disulphide bond formation of conglutin δ from lupin (Lupinus angustifolius) has been also described, with an additional free cysteine residue being present; in the case of 2S albumins from peas (Pisum sativum), the subunits PA1a and PA1b do not appear to be associated by disulphide bridges, being readily separated by chromatography under non-denaturing conditions [17].


2S Albumin Storage Proteins: What Makes them Food Allergens?

Moreno FJ, Clemente A - Open Biochem J (2008)

Schematic representation of the disulphide bond patterns formed between the eight conserved cysteine residues in the 2S albumin family.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2570561&req=5

Figure 1: Schematic representation of the disulphide bond patterns formed between the eight conserved cysteine residues in the 2S albumin family.
Mentions: tions, mainly derived from proteolytic processing; these isoforms may show considerable differences in their structures and biological properties. Nevertheless, it is possible to define the protein structure of a “typical” 2S albumin. These proteins are synthesized as a single larger precursor polypeptide of Mr~18-21 kD, which is co-translationally transported into the lumen of the endoplasmic reticulum. After the formation of four intra-chain disulphide bonds, involving eight conserved cysteine residues, the folded protein is transported into the vacuole where is subsequently processed to a polypeptide of Mr ~12-14 kD and eventually to the large and small subunits of Mr~8-10 and 3-4 kD, respectively [14]. Owing to the conserved skeleton of cysteine residues, the small and large subunits remain associated by two inter-molecular disulphide bonds in the mature form; other two intra-chain disulphide bonds are present within the large subunit. Fig. (1) depicts the typical disulphide bond mapping of the 2S albumins. The conserved scaffold includes that the third and fourth cysteine residues are consecutive in the polypeptide chain (large subunit) and the fifth and sixth cysteine residues are separated by only one residue. The inter-chain disulphide bonds are those formed between cysteine residues 1-5 and 2-3 whereas the intra-chain bridges are formed by the cysteine residues 4-7 and 6-8. A range of variants differing from the “typical” 2S albumins in their structure or mode of biosynthesis has been reported. Such is the case of the major methionine-rich albumin, SFA8, from sunflower (Helianthus annuus) in which post-translational processing seems to be limited to the removal of the signal peptide and the pro-region with no further proteolytic cleavage of the polypeptide chain into large and small subunits [15]. SFA8 is the only 2S albumin isolated and characterized to date that is composed of a single polypeptide chain [16]. Variation in disulphide bond formation of conglutin δ from lupin (Lupinus angustifolius) has been also described, with an additional free cysteine residue being present; in the case of 2S albumins from peas (Pisum sativum), the subunits PA1a and PA1b do not appear to be associated by disulphide bridges, being readily separated by chromatography under non-denaturing conditions [17].

Bottom Line: This review describes the main biochemical, structural and functional properties of these proteins thought to play a role in determining their potential allergenicity. 2S albumins are considered to sensitize directly via the gastrointestinal tract (GIT).The flexible and solvent-exposed hypervariable region of these proteins is immunodominant and has the ability to bind IgE from allergic patients sera.Finally, the interaction of these proteins with other components of the food matrix might influence the absorption rates of immunologically reactive 2S albumins but also in their immune response.

View Article: PubMed Central - PubMed

Affiliation: Instituto de Fermentaciones Industriales (CSIC), C/ Juan de la Cierva 3, 28006 Madrid, Spain.

ABSTRACT
2S albumin storage proteins are becoming of increasing interest in nutritional and clinical studies as they have been reported as major food allergens in seeds of many mono- and di-cotyledonous plants. This review describes the main biochemical, structural and functional properties of these proteins thought to play a role in determining their potential allergenicity. 2S albumins are considered to sensitize directly via the gastrointestinal tract (GIT). The high stability of their intrinsic protein structure, dominated by a well-conserved skeleton of cysteine residues, to the harsh conditions present in the GIT suggests that these proteins are able to cross the gut mucosal barrier to sensitize the mucosal immune system and/or elicit an allergic response. The flexible and solvent-exposed hypervariable region of these proteins is immunodominant and has the ability to bind IgE from allergic patients sera. Several linear IgE-binding epitopes of 2S albumins spanning this region have been described to play a major role in allergenicity; the role of conformational epitopes of these proteins in food allergy is far from being understood and need to be investigated. Finally, the interaction of these proteins with other components of the food matrix might influence the absorption rates of immunologically reactive 2S albumins but also in their immune response.

No MeSH data available.


Related in: MedlinePlus