Alternaria alternata allergen Alt a 1: A unique β-barrel protein dimer found exclusively in fungi

• Published in: Journal of allergy and clinical immunology Vol. 130; no. 1; pp. 241 - 247.e9
• Main Authors: Chruszcz, Maksymilian, PhD, Chapman, Martin D., PhD, Osinski, Tomasz, MSc, Solberg, Robert, MSc, Demas, Matthew, BSc, Porebski, Przemyslaw J., MSc, Majorek, Karolina A., MSc, Pomés, Anna, PhD, Minor, Wladek, PhD
• Format: Journal Article
• Language: English
• Published: United States Mosby, Inc 01-07-2012
• Subjects: Adult; allergens; Allergens - chemistry; Allergens - genetics; Allergens - immunology; Allergens - metabolism; Allergy and Immunology; Alt a 1; Alternaria - immunology; Alternaria - metabolism; Alternaria alternata; Alternaria species; Amino Acid Sequence; Asthma; Child; Computational Biology; Crystallography, X-Ray; Dimerization; Epitopes; Fungal Proteins - chemistry; Fungal Proteins - genetics; Fungal Proteins - immunology; Fungal Proteins - metabolism; Humans; Immunoglobulin E - metabolism; Models, Molecular; molds; oligomeric structure; protein structure; Sequence Alignment; x-ray crystallography; 8-ACA; gi; 8-Aminocaprylic acid; Alt a 1; oligomeric structure; 4-Hydroxy-2,5,6-triaminopyrimidine; DLS; Alternaria species; molds; Asthma; allergens; PDB; protein structure; x-ray crystallography; Dynamic light scattering; 4-HTP; GenInfo Identifier; Protein Data Bank
• ISSN: 0091-6749; 1097-6825
• DOI: 10.1016/j.jaci.2012.03.047

Background Alternaria species is one of the most common molds associated with allergic diseases, and 80% of Alternaria species–sensitive patients produce IgE antibodies to a major protein allergen, Alt a 1. The structure and function of Alt a 1 is unknown. Objective We sought to obtain a high-resolution structure of Alt a 1 using x-ray crystallography and to investigate structural relationships between Alt a 1 and other allergens and proteins reported in the Protein Data Bank. Methods X-ray crystallography was used to determine the structure of Alt a 1 by using a custom-designed set of crystallization conditions. An initial Alt a 1 model was determined by the application of a Ta6 Br122+ cluster and single-wavelength anomalous diffraction. Bioinformatic analyses were used to compare the Alt a 1 sequence and structure with that of other proteins. Results Alt a 1 is a unique β-barrel comprising 11 β-strands and forms a “butterfly-like” dimer linked by a single disulfide bond with a large (1345 Å2 ) dimer interface. Intramolecular disulfide bonds are conserved among Alt a 1 homologs. Currently, the Alt a 1 structure has no equivalent in the Protein Data Bank. Bioinformatics analyses suggest that the structure is found exclusively in fungi. Four previously reported putative IgE-binding peptides have been located on the Alt a 1 structure. Conclusions Alt a 1 has a unique, dimeric β-barrel structure that appears to define a new protein family with unknown function found exclusively in fungi. The location of IgE antibody–binding epitopes is in agreement with the structural analysis of Alt a 1. The Alt a 1 structure will allow mechanistic structure/function studies and immunologic studies directed toward new forms of immunotherapy for Alternaria species–sensitive allergic patients.