NMR Solution Structure of Ole e 6, a Major Allergen from Olive Tree Pollen

Abstract

Ole e 6 is a pollen protein from the olive tree (Olea europaea) that exhibits allergenic activity with a high prevalence among olive-allergic individuals. The threedimensional structure of Ole e 6 has been determined in solution by NMR methods. This is the first experimentally determined structure of an olive tree pollen allergen. The structure of this 50-residue protein is based on 486 upper limit distance constraints derived from nuclear Overhauser effects and 24 torsion angle restraints. The global fold of Ole e 6 consists of two nearly antiparallel ␣-helices, spanning residues 3-19 and 23-33, that are connected by a short loop and followed by a long, unstructured C-terminal tail. Viewed edge-on, the structured N terminus has a dumbbell-like shape with the two helices on the outside and with the hydrophobic core, mainly composed of 3 aromatic and 6 cysteine residues, on the inside. All the aromatic rings lie on top of and pack against the three disulfide bonds. The lack of thermal unfolding, even at 85°C, indicates a high conformational stability. Based on the analysis of the molecular surface, we propose five plausible epitopes for IgE recognition. The results presented here provide the structural foundation for future experiments to verify the antigenicity of the proposed epitopes, as well as to design novel hypoallergenic forms of the protein suitable for diagnosis and treatment of type-I allergies. In addition, three-dimensional structure features of Ole e 6 are discussed to provide a basis for future functional studies.

Solution structure of the phytotoxic protein PcF: The first characterized member of the Phytophthora PcF toxin family

“…Based on fold superposition, charge similarity, extracellular location, and cysteines relative abundance, a few small all‐α‐proteins were retained. They included three scorpion toxins acting as K + ‐channel inhibitors (OmTx1, OmTx3,10 and κ‐hefutoxin11) and Ole e 6 from Olea europaea , a pollen protein of unknown biochemical function in plant but acting as allergen in humans 12. The proteins, with respect to PcF, display very similar orientation of the two α‐helices, in all cases kept in place by multiple disulphide bonds, whereas their interhelical loop appears shorter and poorly superimposed (see Fig.…”

Solution structure of the C‐terminal domain of Ole e 9, a major allergen of olive pollen

“…In the case of 15 N-or 15 N-13 C tagged proteins, the same slight modifications described previously (Treviño et al 2004) were introduced. All samples were analyzed by amino acid analysis, N-terminal end sequencing, and mass spectroscopy.…”

“…To date, 10 allergens from olive pollen, Ole e 1-Ole e 10, have been characterized (Rodríguez et al 2002;Barral et al 2004), but only the three-dimensional (3D) structure of Ole e 6 has been determined (Treviño et al 2004). Among them, Ole e 9 is important because it has been described as a potential cause of adverse reactions in specific immunotherapy (SIT) (Duffort et al 2006).…”

Structure of allergens and structure based epitope predictions

“…Unstructured regions are typically missing in X-ray structures and are characterized by poorly defined NMR structure bundles and differences in their relaxation behavior compared to well-structured parts. Relatively large unstructured regions were found for example in the mugwort pollen allergen Art v 1 [26], the tropical mite allergen Blo t 5 [27] and the olive tree pollen allergen Ole e 6 [28]. In contrast to IgG, IgE binds mainly to structured proteins.…”

“…On the other hand this allergen is very stable on the nanosecond-picosecond time range based on higher generalized order parameters S 2 in the antibody interaction site. The mobility of allergens is often significantly reduced by the formation of disulfide bonds, like in Ole e 6 [28], Ara h 6 [30] or Amb t 5 [11] or by the binding of e.g., calcium ions as for Bet v 4 [31].…”