title: Evolutionary distance from human homologs reflects allergenicity of animal food proteins.
abstract: BACKGROUND
  In silico analysis of allergens can identify putative relationships among protein sequence, structure, and allergenic properties. Such systematic analysis reveals that most plant food allergens belong to a restricted number of protein superfamilies, with pollen allergens behaving similarly.
  
  
  OBJECTIVE
  We have investigated the structural relationships of animal food allergens and their evolutionary relatedness to human homologs to define how closely a protein must resemble a human counterpart to lose its allergenic potential.
  
  
  METHODS
  Profile-based sequence homology methods were used to classify animal food allergens into Pfam families, and in silico analyses of their evolutionary and structural relationships were performed.
  
  
  RESULTS
  Animal food allergens could be classified into 3 main families--tropomyosins, EF-hand proteins, and caseins--along with 14 minor families each composed of 1 to 3 allergens. The evolutionary relationships of each of these allergen superfamilies showed that in general, proteins with a sequence identity to a human homolog above approximately 62% were rarely allergenic. Single substitutions in otherwise highly conserved regions containing IgE epitopes in EF-hand parvalbumins may modulate allergenicity.
  
  
  CONCLUSIONS
  These data support the premise that certain protein structures are more allergenic than others. Contrasting with plant food allergens, animal allergens, such as the highly conserved tropomyosins, challenge the capability of the human immune system to discriminate between foreign and self-proteins. Such immune responses run close to becoming autoimmune responses.
  
  
  CONCLUSIONS
  Exploiting the closeness between animal allergens and their human homologs in the development of recombinant allergens for immunotherapy will need to consider the potential for developing unanticipated autoimmune responses.
authors.affiliation: Institute of Food Research, Norwich, United Kingdom.
authors.forename: John A
authors.initials: JA
authors.lastname: Jenkins
authors.forename: Heimo
authors.initials: H
authors.lastname: Breiteneder
authors.forename: E N Clare
authors.initials: EN
authors.lastname: Mills
mesh_terms: D000485:Allergens / Q000145:classification / Q000235:genetics / Q000276:immunology*; D000818:Animals; D002364:Caseins / Q000009:adverse effects / Q000276:immunology; D002417:Cattle; D019295:Computational Biology / Q000379:methods; D004044:Dietary Proteins / Q000009:adverse effects / Q000276:immunology*; D020832:EF Hand Motifs / Q000276:immunology; D019143:Evolution, Molecular; D005512:Food Hypersensitivity / Q000276:immunology*; D006801:Humans; D010940:Plant Proteins / Q000009:adverse effects / Q000276:immunology; D017386:Sequence Homology, Amino Acid; D014335:Tropomyosin / Q000009:adverse effects / Q000276:immunology
chemical_list: D000485:Allergens; D002364:Caseins; D004044:Dietary Proteins; D010940:Plant Proteins; D014335:Tropomyosin