Revealing the Diverse Allergenic Protein Repertoire of Six Widely Consumed Crab Species: A Species-Specific Allergen in King Crab

Background: Shellfish allergy poses a significant health risk affecting up to 2% of the global population. Comprehensive allergen profiling across species is crucial for improving diagnostics and therapies, given the challenges posed by cross-reactivity. This study aims to identify and compare the allergen profiles of six widely consumed edible crab species. Methods: Muscle proteins were extracted from five brachyurans (true crabs) including Charybdis feriata, Portunus pelagicus, Scylla paramamosain, Chionoecetes opilio, and Eriocheir sinensis, as well as the king crab Paralithodes camtschaticus, and were analyzed for IgE reactivity with serum samples from 29 crab-allergic individuals and three nonallergic controls. IgE-binding proteins were identified by immunoblotting followed by mass spectrometry. Recombinant king crab allergen was purified and tested on ELISA against samples from 50 crab-allergic individuals, with its specific IgE reactivity evaluated by inhibition ELISA and immunoblot. Comparison of the gene expression of the identified allergens along with reported epitopes was revealed through comparative transcriptomics and multiple sequence alignments. Results: IgE reactivity was detected only in serum samples from crab-allergic individuals. Immunoblotting distinguished eight putative crab allergens and three registered crab allergens. The protein and allergen profiles of the king crab were distinct from the brachyuran crab species based on dendrogram analysis; malate dehydrogenase (MDH) was distinctly reactive only in king crab with 41.4% sensitization on immunoblot, while recombinant MDH displayed a 14% sensitization rate, leading to its registration as Para c 11. MDH homologs from true crabs showed minimal inhibition to Para c 11 (< 10%). Based on transcriptomic analysis, the identified crab allergens showed similar expression across species, while the sequence and epitope similarity exceeded 68%. Conclusion: The study provides molecular insights into crab allergen diversity and highlights the potential for species-specific crab allergies with Para c 11 as a potential king crab-specific allergen, paving the way for personalized and advanced component-resolved diagnostics.