Searching for allergens in maize kernels via proteomic tools

Up to the present, only one major allergen had been univocally identified by chemical analysis (N-terminal sequencing) in the salt-extractable (cytoplasmic) protein fraction of maize kernels (Zea mays): the lipid transfer protein (Pastorello et al., Allergy Clin. Immunol. 2000;106:744-751). In the present study, two-dimensional maps of kernel flour have been set up, the proteins transferred to nitrocellulose membranes and confronted with sera of various patients allergic to maize proteins. Via spot excision and Orbitrap mass analysis, the following new allergens have been identified: vicilin, globulin-2, 50 kDa gamma-zein, endo-chitinase, thioredoxin and trypsin inhibitor. Vicilin was found to be composed of a string of six spots, all of them allergenic; also globulin-2 was composed of a string of five spots, exhibiting equivalent allergenicity. The 50 kDa gamma-zein, found here in the maize flour soluble fraction, is identical to the 50 kDa allergen reported by Pasini et al. (Allergy 2002; 57:98-106), but present in the insoluble fraction and solubilized via -S-S- reducing agents. However, the form here described might be a truncated species, since it exhibits an apparent Mr, in SDS-PAGE, of ca. 35 kDa. The homology of three of them (vicilin, globulin-2 and thioredoxin) with other vegetable systems has been investigated via BLAST analysis, the ones with highest homology belonging to rice, wheat and barley. The present data add a non-negligible amount of previously unreported allergens to the scanty panorama of maize proteins.