Molecular Characterization of Major Cat Allergen Fel d 1: EXPRESSION OF HETERODIMER BY USE OF A BACULOVIRUS EXPRESSION SYSTEM

Fel d 1 is a major cat allergen inducing allergic rhinitis and asthma in sensitized individuals. It has a more complex structure when compared with other allergens and therefore expression of recombinant Fel d 1 has been considered a challenge. The present study shows for the first time that a Baculovirus expression system is able to produce an intact rFel d 1 molecule that is glycosylated and structurally equivalent to the natural cat allergen, nFel d 1. Enzymatic digestion of rFel d 1 and further analysis by use of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) resulted in a complete coverage of the amino acid sequence of rFel d 1. In addition, the three disulfide bridges at the positions alpha70-beta7, alpha44-beta48, and alpha3-beta73 were verified. The N-glycan structure of rFel d 1 was investigated by a combination of MALDI-TOF MS and monosaccharide analysis by high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAC). The N-glycosylation analyses of rFel d 1 refer to a pattern of glycoforms including core alpha1.3-fucosylation that is different from nFel d 1. Further characterization by use of human serum IgE, histamine release, and lymphocyte proliferation assays demonstrated that the immunological characteristics of rFel d 1 are similar to those of nFel d 1. Detailed characterization of both natural and recombinant allergens provides tools to explore immunological mechanisms associated with allergen sensitization and desensitization.