Allergenic relevance of nonspecific lipid transfer proteins 2: Identification and characterization of Api g 6 from celery tuber as representative of a novel IgE-binding protein family

Mol Nutr Food Res. 2013 Nov;57(11):2061-70. doi: 10.1002/mnfr.201300085. Epub 2013 Aug 5.


Scope: Apium graveolens represents a relevant food allergen source linked with severe systemic reactions. We sought to identify an IgE-binding nonspecific lipid transfer protein (nsLTP) in celery tuber.

Methods and results: A low molecular weight protein exclusively present in celery tuber was purified and designated Api g 6. The entire protein sequence was obtained by MS and classified as member of the nsLTP2 family. Api g 6 is monomeric in solution with a molecular mass of 6936 Da. The alpha-helical disulfide bond-stabilized structure confers tremendous thermal stability (Tm > 90°C) and high resistance to gastrointestinal digestion. Endolysosomal degradation demonstrated low susceptibility and the presence of a dominant peptide cluster at the C-terminus. Thirty-eight percent of A. graveolens allergic patients demonstrated IgE reactivity to purified natural Api g 6 in ELISA and heat treatment did only partially reduce its allergenic activity. No correlation in IgE binding and limited cross-reactivity was observed with Api g 2 and Art v 3, nsLTP1 from celery stalks and mugwort pollen.

Conclusion: Api g 6, a novel nsLTP2 from celery tuber represents the first well-characterized allergen in this protein family. Despite similar structural and physicochemical features as nsLTP1, immunological properties of Api g 6 are distinct which warrants its inclusion in molecule-based diagnosis of A. graveolens allergy.

Keywords: Apium graveolens; Celery tuber; IgE reactivity; Nonspecific lipid transfer protein 2; Plant food allergy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Allergens / analysis*
  • Allergens / immunology
  • Antigens, Plant / analysis
  • Antigens, Plant / immunology
  • Apium / chemistry*
  • Apium / immunology*
  • Carrier Proteins / analysis
  • Carrier Proteins / immunology*
  • Circular Dichroism
  • Cross Reactions
  • Food Hypersensitivity / diagnosis
  • Food Hypersensitivity / immunology
  • Galectin 3 / analysis
  • Galectin 3 / immunology*
  • Gastrointestinal Tract / metabolism
  • Humans
  • Molecular Weight
  • Plant Proteins / analysis*
  • Plant Proteins / immunology
  • Proteolysis


  • Allergens
  • Antigens, Plant
  • Carrier Proteins
  • Galectin 3
  • Plant Proteins
  • sterol carrier proteins