Transient Dimers of Allergens

Abstract

BackgroundAllergen-mediated cross-linking of IgE antibodies bound to the FcεRI receptors on the mast cell surface is the key feature of the type I allergy. If an allergen is a homodimer, its allergenicity is enhanced because it would only need one type of antibody, instead of two, for cross-linking.Methodology/Principal FindingsAn analysis of 55 crystal structures of allergens showed that 80% of them exist in symmetric dimers or oligomers in crystals. The majority are transient dimers that are formed at high protein concentrations that are reached in cells by colocalization. Native mass spectrometric analysis showed that native allergens do indeed form transient dimers in solution, while hypoallergenic variants of them exist almost solely in the monomeric form. We created a monomeric Bos d 5 allergen and show that it has a reduced capability to induce histamine release.Conclusions/SignificanceThe results suggest that dimerization would be a very common and essential feature for allergens. Thus, the preparation of purely monomeric variants of allergens could open up novel possibilities for specific immunotherapy.

A Hypoallergenic Polygalacturonase Isoform from Olive Pollen Is Implicated in Pollen-Pollen Cross-Reactivity

“…In this sense, the production of hypoallergens is an important strategy to obtain new molecules with improved qualities to be used as diagnostic and/or therapeutic tools in clinical trials, which has led to the development of multiple studies focused on the development of hypoallergenic derivatives for highly prevalent allergens [26]. Although multiple approaches based on genetic engineering have been used to obtain allergenic variants with decreased IgE binding ability but able to induce an IgG-associated response [27-30], the identification of natural hypoallergenic molecules makes them useful as their 3D folding is more prone to be identical to that of the sensitizing allergen [25, 31]. Thus, the availability of recombinant isoforms of an allergen with equivalent antigenic but lower allergenic properties may enable the identification of the features that make an allergen a molecule able to stimulate the immune system, in addition to its clinical potential.…”

Molecular Dynamics of Major Allergens from Alternaria, Birch Pollen and Peach

“…While it has been claimed that dimer stabilization should be due to this presumed disulfide linkage, [10,36] mass spectra obtained under denaturing solution conditions have provided evidence that Alt a 1 dimerization is not mediated by the disulfide bond. [7] It must be also noted that whereas four cysteines that make intramolecular disulfide bonds (residues 74, 89, 128, and 140) are conserved among all the Alt a 1 homologs, Cys30 is only conserved among the closest homologs. We studied (i) the dimer with the intermolecular disulfide bond kept along the MD simulation ("dimer SSbridge" in what follows), (ii) the equivalent dimer without that link (named just "dimer") and (iii) the dimer in PDB entry 4AUD that lacks six N-terminal amino acids including residue 30 (named "dimer (4AUD)").…”

“…Interestingly, the dimer with the disulfide bond between Cys30 residues ("dimer SSbr" data) is not more rigid than the dimer without this linkage ("dimer" data) a result that should confirm the earlier suggestion that Alt a 1 dimerization is not mediated by the disulfide bond. [7] Even though Cys30 shows an obviously greater motion in the dimer without its disulfide bond (RMSD~2.7 ) than in the dimer with it (RMSD1 .4 ), this residue is much more flexible in monomer (RMSD = 6.6 ) or in tetramer (RMSD > 5.1 ) states, a result that indicates a far greater conformational freedom of the N-terminal tail in monomer or tetramer than in dimers (Figs. 2 A-2 D): the oscillations of RMSD for Cys30 are much greater in the monomer than in the dimers regardless disulfide bond formation (Figure 2 H).…”

“…A computational analysis of 55 allergen X-ray structures found that 80 % of them can exist as symmetric dimers or oligomers in crystals. [7] This report raised the suggestion that many of these molecular complexes aggregates could be transient dimers difficult to observe at normal concentrations in cells but becoming favored if concentration increases locally as it should occur on antigenpresenting cells or antigen-antibody complexes. [7] We have recently extended the oligomerization analysis to 84 allergen X-ray structures using crystal information together with a new computational tool that uses evolutionary information to address dimer formation.…”

“…[7] This report raised the suggestion that many of these molecular complexes aggregates could be transient dimers difficult to observe at normal concentrations in cells but becoming favored if concentration increases locally as it should occur on antigenpresenting cells or antigen-antibody complexes. [7] We have recently extended the oligomerization analysis to 84 allergen X-ray structures using crystal information together with a new computational tool that uses evolutionary information to address dimer formation. [8] Our study lowered the proportion of allergens with oligomeric states down to 66 % although it still seems clear that oligomerization is a common feature of allergens.…”