OLIGOMERIZATION OF PROFILINS FROM BIRCH, MAN AND YEAST - PROFILIN, A LIGAND FOR ITSELF

Profilins are structurally well conserved low molecular weight (12-15 kDa) eukaryotic proteins which interact with a variety of physiologica l ligands: (1) cytoskeletal components, e.g., actin: (2) polyphosphoin ositides, e.g., phosphatidylinositol-4,5-bisphosphate; (3) proline-ric h proteins, e.g., formin homology proteins and vasodilatator-stimulate d phosphoprotein. Profilins may thus link the microfilament system wit h signal transduction pathways. Plant profilins have recently been sho wn to be highly crossreactive allergens which bind to IgE antibodies o f allergic patients and thus cause symptoms of type I allergy. We expr essed and purified from Escherichia coli profilins from birch pollen ( Betula Betula verrucosa), humans (Homo sapiens) and yeast (Schizosacch aromyces pombe) and demonstrated that each of these profilins is able to form stable homo- and heteropolymers via disulphide bonds in vitro. Circular dichroism analysis of oxidized (polymeric) and reduced (mono meric) birch pollen profilin indicates that the two states have simila r secondary structures. Using I-125-labeled birch pollen, yeast and hu man profilin in overlay experiments, we showed that disulphide bond fo rmation between profilins can be disrupted under reducing conditions, while reduced as well as oxidized profilin states bind to actin and pr ofilin-specific antibodies. Exposure of profilin to oxidizing conditio ns, such as when pollen profilins are liberated on the surface of the mucosa of atopic patients, may lead to profilin polymerization and thu s contribute to the sensitization capacity of profilin as an allergen.