Crystallographically mapped ligand binding differs in high and low IgE binding isoforms of birch pollen allergen bet v 1.
The ability of pathogenesis-related proteins of family 10 to bind a broad spectrum of ligands is considered to play a key role for their physiological and pathological functions. In particular, Bet v 1, an archetypical allergen from birch pollen, is described as a highly promiscuous ligand acceptor. However, the detailed recognition mechanisms, including specificity factors discriminating binding properties of naturally occurring Bet v 1 variants, are poorly understood. Here, we report crystal structures of Bet v 1 variants in complex with an array of ligands at a resolution of up to 1.2 Å. Residue 30 within the hydrophobic pocket not only discriminates in high and low IgE binding Bet v 1 isoforms but also induces a drastic change in the binding mode of the model ligand deoxycholate. Ternary crystal structure complexes of Bet v 1 with several ligands together with the fluorogenic reporter 1-anilino-8-naphthalene sulfonate explain anomalous fluorescence binding curves obtained from 1-anilino-8-naphthalene sulfonate displacement assays. The structures reveal key interaction residues such as Tyr83 and rationalize both the binding specificity and promiscuity of the so-called hydrophobic pocket in Bet v 1. The intermolecular interactions of Bet v 1 reveal an unexpected complexity that will be indispensable to fully understand its roles within the physiological and allergenic context.
Structural Biology Group, Department of Molecular Biology, University of Salzburg, A-5020 Salzburg, Austria.
Stefan
S
Kofler
Claudia
C
Asam
Ulrich
U
Eckhard
Michael
M
Wallner
Fátima
F
Ferreira
Hans
H
Brandstetter
D000485:Allergens / Q000378:metabolism; D000817:Anilino Naphthalenesulfonates / Q000737:chemistry / Q000378:metabolism; D052179:Antigens, Plant / Q000737:chemistry* / Q000378:metabolism; D029662:Betula / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D007073:Immunoglobulin E / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D008958:Models, Molecular; D011058:Pollen / Q000737:chemistry; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism
D000485:Allergens; D000817:Anilino Naphthalenesulfonates; D052179:Antigens, Plant; D008024:Ligands; D020033:Protein Isoforms; C061312:Bet v 1 allergen, Betula; D007073:Immunoglobulin E; C027132:1-anilino-8-naphthalenesulfonate