Identification of conformational IgE-binding epitopes of Pacific mackerel (Scomber japonicus) parvalbumin.

Parvalbumin (PV), a Ca2+-binding 12 kDa protein unique to vertebrates, represents a major allergen in teleost fish. Considering that its IgE reactivity is primarily conformation-dependent, this study aimed to identify the conformational IgE-binding epitopes of teleost fish PVs, using Pacific mackerel (Scomber japonicus) PV as a model. By examining the relative IgE reactivity of various single-residue substitution mutants to the wild-type PV, two epitope regions (epitope 1 with 12 residues and epitope 2 with 5 residues) were identified on the molecular surface. The degree of conservation of the identified epitope residues is consistent with the strong cross-reactivity among teleost fish PVs and the weak cross-reactivity between teleost fish PVs and PVs of cartilaginous fish, amphibians, reptiles and birds. In mammalian PVs, three epitope residues (A48, D79 and K107) are substituted with amino acids of different properties, which is presumably the molecular basis for no cross-reactivity with teleost fish PVs.