Comparative Analysis of Asian Carps Parvalbumin Reveals the Evolutionary Divergence Pattern of a Major Fish Allergen

Background: Asian carps are popular freshwater fish species in Hong Kong and served as an important protein source for infants. Grass carp parvalbumin was reported to have higher allergenicity than other commercially important fishes (salmon and cod) in terms of IgE reactivity. Objective To identify allergens in Asian carps and study the divergence pattern of allergens. Method Three complete Asian carps’ genomes were constructed by hybrid assembly approach. All the homologs of known and putative allergens were identified based on sequence homology at the genomic level. The gene structures, expression level and protein conformations of parvalbumin were revealed using bioinformatics tools. Results Parvalbumin is the major allergen in grass carp tested by indirect ELISA. Nine homologs of parvalbumin were identified in the genome of grass carp, in which Cid_PV2 exhibited highest sequence similarity to the reported group 1 allergen of grass carp, Cten i 1. Similarly, ten parvalbumin homologs were identified in the genome of bighead and black carp respectively, in which Mpi_PV7 and Hno_PV7 were identified as the putative allergenic homologs. The expression profile of parvalbumin revealed alternative usage of homologs in different tissues of Asian carps. Moreover, gene copy numbers of parvalbumin gradually expanded in bony fish and two gene clusters of parvalbumin were identified inside the genomes of Asian carps. Conclusion All the homologs of Asian carps’ parvalbumin were accurately identified and gene divergence contributed to the formation of allergenic homologs. Together with a comprehensive gene sequence profile of carps’ parvalbumin, those could be applied to achieve a more precise clinical diagnostic test and would ultimately assist the design of preventive treatment by immunotherapy of fish allergy.