title: Structural and bioinformatic analysis of the kiwifruit allergen Act d 11, a member of the family of ripening-related proteins.
abstract: The allergen Act d 11, also known as kirola, is a 17 kDa protein expressed in large amounts in ripe green and yellow-fleshed kiwifruit. Ten percent of all kiwifruit-allergic individuals produce IgE specific for the protein. Using X-ray crystallography, we determined the first three-dimensional structures of Act d 11, produced from both recombinant expression in Escherichia coli and from the natural source (kiwifruit). While Act d 11 is immunologically correlated with the birch pollen allergen Bet v 1 and other members of the pathogenesis-related protein family 10 (PR-10), it has low sequence similarity to PR-10 proteins. By sequence Act d 11 appears instead to belong to the major latex/ripening-related (MLP/RRP) family, but analysis of the crystal structures shows that Act d 11 has a fold very similar to that of Bet v 1 and other PR-10 related allergens regardless of the low sequence identity. The structures of both the natural and recombinant protein include an unidentified ligand, which is relatively small (about 250 Da by mass spectrometry experiments) and most likely contains an aromatic ring. The ligand-binding cavity in Act d 11 is also significantly smaller than those in PR-10 proteins. The binding of the ligand, which we were not able to unambiguously identify, results in conformational changes in the protein that may have physiological and immunological implications. Interestingly, the residue corresponding to Glu45 in Bet v 1 (Glu46), which is important for IgE binding to the birch pollen allergen, is conserved in Act d 11, even though it is not in other allergens with significantly higher sequence identity to Bet v 1. We suggest that the so-called Gly-rich loop (or P-loop), which is conserved in all PR-10 allergens, may be responsible for IgE cross-reactivity between Bet v 1 and Act d 11.
authors: Department of Chemistry and Biochemistry, University of South Carolina, 631 Sumter Street, Columbia, SC 29208, USA; Department of Molecular Physiology and Biological Physics, University of Virginia, 1340 Jefferson Park Avenue, Charlottesville, VA 22908, USA. Electronic address: chruszcz@mailbox.sc.edu.
authors: Maksymilian
authors: M
authors: Chruszcz
authors: Maria Antonietta
authors: MA
authors: Ciardiello
authors: Tomasz
authors: T
authors: Osinski
authors: Karolina A
authors: KA
authors: Majorek
authors: Ivana
authors: I
authors: Giangrieco
authors: Jose
authors: J
authors: Font
authors: Heimo
authors: H
authors: Breiteneder
authors: Konstantinos
authors: K
authors: Thalassinos
authors: Wladek
authors: W
authors: Minor
mesh_terms: D029042:Actinidia / Q000235:genetics / Q000276:immunology* / Q000502:physiology; D000485:Allergens / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D000595:Amino Acid Sequence; D052179:Antigens, Plant / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D019295:Computational Biology; D005638:Fruit / Q000235:genetics / Q000276:immunology* / Q000502:physiology; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012701:Serotonin / Q000737:chemistry / Q000378:metabolism
chemical_list: C550604:Act d 4 allergen, Actinidia deliciosa; D000485:Allergens; D052179:Antigens, Plant; D010940:Plant Proteins; D011994:Recombinant Proteins; D012701:Serotonin
keywords: Act d 11; Allergen; Bet v 1; Food allergy; Kirola; Kiwifruit; MLP; PDB; PR-10; Protein Data Bank; RMSD; RRP; major latex protein; pathogenesis-related proteins family 10; ripening related protein; root mean square deviation
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