TY - JOUR
T1 - Immunological and biological properties of Bet v 4, a novel birch polen allergen with two EF-hand calcium-binding domains
AU - Engel, E.
AU - Richter, K.
AU - Briza, P.
AU - Simon, B.
AU - Rheinberger, H.-J.
AU - Breitenbach, M.
AU - Ferreira, F.
AU - Obermeyer, G.
AU - Kungl, A.J.
AU - Auer, M.
AU - Ebner, C.
N1 - Medline is the source for the MeSH terms of this document.
PY - 1997/11/7
Y1 - 1997/11/7
N2 - We have isolated a cDNA clone coding for a birch pollen allergen, Bet v 4. The deduced amino acid sequence of Bet v 4 contained two typical EF-hand calcium-binding domains. Sequence similarities of Bet v 4 to calmodulin are primarily confined to the calcium-binding domains. However, significant sequence similarities extending outside the Ca-binding sites were found with a recently described group of pollen-specific allergens of Brassica and Bermuda grass. Both EF-hand domains of Bet v 4 are able to bind Ca, as demonstrated by Ca blot overlay of wild type and calcium-binding deficient mutants of Bet v 4. Among pollen-allergic patients, protein-bound Ca was not an absolute requirement for IgE recognition of Bet v 4. However, disruption of the carboxyl-terminal Ca-binding domain indicated that most IgE antibodies from allergic patients are directed against this site. IgE inhibition experiments suggested that Bet v 4 represents a highly cross-reactive pollen allergen. Pre-absorption of allergic sera with Bet v 4 drastically reduced IgE binding to proteins of similar molecular weight in pollen extracts from distantly related plant species (e.g. timothy grass, mugwort, lily) but not in extracts from plant-derived foodstuff. To test for a possible biological role in pollen germination and tube growth, we introduced recombinant Bet v 4 protein into growing lily pollen tubes by iontophoresis. As a result, cytoplasmic streaming stopped in the vicinity of the electrode tip, and a slight depolarization of the membrane voltage was measured. These effects were not observed with Ca -binding deficient mutants of Bet v 4. Thus, Bet v 4 and homologous proteins represent a new class of polle-specific Ca-binding allergens that may have a physiological role as inhibitors of cytoplasmic streaming in outgrowing pollen tubes.
AB - We have isolated a cDNA clone coding for a birch pollen allergen, Bet v 4. The deduced amino acid sequence of Bet v 4 contained two typical EF-hand calcium-binding domains. Sequence similarities of Bet v 4 to calmodulin are primarily confined to the calcium-binding domains. However, significant sequence similarities extending outside the Ca-binding sites were found with a recently described group of pollen-specific allergens of Brassica and Bermuda grass. Both EF-hand domains of Bet v 4 are able to bind Ca, as demonstrated by Ca blot overlay of wild type and calcium-binding deficient mutants of Bet v 4. Among pollen-allergic patients, protein-bound Ca was not an absolute requirement for IgE recognition of Bet v 4. However, disruption of the carboxyl-terminal Ca-binding domain indicated that most IgE antibodies from allergic patients are directed against this site. IgE inhibition experiments suggested that Bet v 4 represents a highly cross-reactive pollen allergen. Pre-absorption of allergic sera with Bet v 4 drastically reduced IgE binding to proteins of similar molecular weight in pollen extracts from distantly related plant species (e.g. timothy grass, mugwort, lily) but not in extracts from plant-derived foodstuff. To test for a possible biological role in pollen germination and tube growth, we introduced recombinant Bet v 4 protein into growing lily pollen tubes by iontophoresis. As a result, cytoplasmic streaming stopped in the vicinity of the electrode tip, and a slight depolarization of the membrane voltage was measured. These effects were not observed with Ca -binding deficient mutants of Bet v 4. Thus, Bet v 4 and homologous proteins represent a new class of polle-specific Ca-binding allergens that may have a physiological role as inhibitors of cytoplasmic streaming in outgrowing pollen tubes.
UR - http://www.scopus.com/inward/record.url?partnerID=yv4JPVwI&eid=2-s2.0-0030662265&md5=2cf07300b843dcc42993cff509fb0818
U2 - 10.1074/jbc.272.45.28630
DO - 10.1074/jbc.272.45.28630
M3 - Article
AN - SCOPUS:0030662265
SN - 0021-9258
VL - 272
SP - 28630
EP - 28637
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 45
ER -