Physicochemical, structural, and immunological characterization of recombinant Mal d 1.02 allergen in Mexican pediatric patients. A valuable tool for diagnosing.

Apple allergy is a manifestation of pollen-food allergy syndrome (PFAS). Mal d 1 is the major apple allergen and a key driver of cross-reactivity with birch and related tree pollens. Its biochemical properties remain incompletely characterized. This work aimed to comprehensively characterize the physicochemical, structural, and immunological properties of a recombinant Mal d 1 (rMal d 1) isoform and to assess its clinical relevance in apple-allergic Mexican pediatric patients (MPP) with PFAS. Its molecular mass, structural stability, folding, resistance to denaturation, and proteolysis were analyzed. Its IgE reactivity, skin prick tests (SPT), and basophil activation tests (BAT) were performed in MPP. The protein was named rMal d 1.02 since its primary structure identity was 98% with this isoallergen group. It was monomeric and exhibited fully reversible unfolding under heat and urea denaturation, significant stability under acidic pH, and high resistance to trypsin but susceptibility to pepsin. It demonstrated IgE reactivity, and SPT and BAT positivity in allergic patients. Due to its immunoreactivity, it highlights its significance as a key allergen in MPP. Its resistance to digestion and denaturation may explain persistent allergenicity after food processing. rMal d 1.02 is valuable for diagnosing and may inform future immunotherapeutic approaches.