title: Various cross-reactivity of the grass pollen group 4 allergens: crystallographic study of the Bermuda grass isoallergen Cyn d 4.
abstract: The structure of Cyn d 4, the group 4 allergen from Bermuda grass, is reported at 2.15 Å resolution and is the first crystal structure of a naturally isolated pollen allergen. A conserved N-terminal segment that is only present in the large isoallergens forms extensive interactions with surrounding residues and hence greatly enhances the structural stability of the protein. Cyn d 4 contains an FAD cofactor that is covalently linked to His88 and Cys152. To date, all identified bicovalent flavoproteins are oxidases and their substrates are either sugars or secondary metabolites. A deep large hydrophobic substrate-binding cleft is present. Thus, Cyn d 4 may be an oxidase that is involved in the biosynthesis of a pollen-specific metabolite. Cyn d 4 shares ~70% sequence identity with the Pooideae group 4 allergens. Various cross-reactivities between grass pollen group 4 allergens have previously been demonstrated using sera from allergic patients. The protein surface displays an unusually large number of positively charged clusters, reflecting the high pI of ~10. 38 decapeptides that cover the solvent-accessible sequences did not show any significant IgE-binding activity using sera with high Cyn d 4 reactivity from four patients, suggesting that the IgE epitopes of Cyn d 4 are predominantly conformational in nature. Several group 4 structures were then modelled and their potential cross-reactive and species-specific IgE epitopes were proposed.
authors.affiliation: Department of Life Sciences, National Yang-Ming University, Taipei 11221, Taiwan.
authors.forename: Tse-Hao
authors.initials: TH
authors.lastname: Huang
authors.forename: Ho-Jen
authors.initials: HJ
authors.lastname: Peng
authors.forename: Song-Nan
authors.initials: SN
authors.lastname: Su
authors.forename: Shwu-Huey
authors.initials: SH
authors.lastname: Liaw
mesh_terms: D000485:Allergens / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*; D052179:Antigens, Plant / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D003429:Cross Reactions / Q000276:immunology; D018360:Crystallography, X-Ray; D031744:Cynodon / Q000737:chemistry* / Q000276:immunology; D000939:Epitopes / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D006801:Humans; D011058:Pollen / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*
chemical_list: D000485:Allergens; D052179:Antigens, Plant; C577577:Cyn d 4 allergen, Cynodon dactylon; D000939:Epitopes