The major birch allergen, Bet v 1, shows affinity for a broad spectrum of physiological ligands.
Bet v 1 is a 17-kDa protein abundantly present in the pollen of the White birch tree and is the primary cause of birch pollen allergy in humans. Its three-dimensional structure is remarkable in that a solvent-accessible cavity traverses the core of the molecule. The biological function of Bet v 1 is unknown, although it is homologous to a family of pathogenesis-related proteins in plants. In this study we first show that Bet v 1 in the native state is able to bind the fluorescent probe 8-anilino-1-naphthalenesulfonic acid (ANS). ANS binds to Bet v 1 with 1:1 stoichiometry, and NMR data indicate that binding takes place in the cavity. Using an ANS displacement assay, we then identify a range of physiologically relevant ligands, including fatty acids, flavonoids, and cytokinins, which generally bind with low micromolar affinity. The ability of these ligands to displace ANS suggests that they also bind in the cavity, although the exact binding sites seem to vary among different ligands. The cytokinins, for example, seem to bind at a separate site close to ANS, because they increase the fluorescence of the ANS. Bet v 1 complex. Also, the fluorescent sterol dehydroergosterol binds to Bet v 1 as demonstrated by direct titrations. This study provides the first qualitative and quantitative data on the ligand binding properties of this important pollen allergen. Our findings indicate that ligand binding is important for the biological function of Bet v 1.
Mogensen
Jesper E
JE
Department of Biotechnology, Institute of Life Sciences, Aalborg University, Sohngaardsholmsvej 49, Aalborg DK-9000, Denmark.
Wimmer
Reinhard
R
Larsen
Jørgen N
JN
Spangfort
Michael D
MD
Otzen
Daniel E
DE
D000485:Allergens; D000817:Anilino Naphthalenesulfonates / Q000378:metabolism; D052179:Antigens, Plant; D003583:Cytokinins / Q000378:metabolism; D004875:Ergosterol / Q000031:analogs & derivatives* / Q000378:metabolism; D005415:Flavins / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D010940:Plant Proteins / Q000378:metabolism*
D000485:Allergens; D000817:Anilino Naphthalenesulfonates; D052179:Antigens, Plant; D003583:Cytokinins; D005415:Flavins; D008024:Ligands; C109472:PRUA1 protein, Prunus avium; D010940:Plant Proteins; C010905:dehydroergosterol; C061312:Bet v 1 allergen, Betula; D004875:Ergosterol