Cross-reactivity and cross-epitopes analysis of sarcoplasmic calcium binding protein from Portunus trituberculatus and Litopenaeus vannamei.

Highly conserved allergens in crab and shrimp readily trigger severe cross-reactivity among crustaceans. Most existing studies on crab-shrimp cross-reactivity focus on tropomyosin (TM), while systematic research on sarcoplasmic calcium binding protein (SCP)-mediated cross-reactivity remains insufficient, and no theoretical framework is available for precise diagnosis targeting SCP cross-epitopes. This study aimed to investigate the cross-reactive properties of SCP from crab and shrimp, identify cross-reactive epitopes, and provide theoretical support for the diagnosis of cross-reactivity induced by crustaceans. In our research, the SCP derived from Portunus trituberculatus (Por t 4) and Litopenaeus vannamei (Lit v 4) were selected as research objects. Firstly, natural Por t 4 and recombinant Por t 4 were prepared, and they were found to exhibit similar IgG/IgE reactivity. Afterwards, Lit v 4 was prepared using the prokaryotic expression strain constructed in our laboratory. Basophil activation test results demonstrated that both Por t 4 and Lit v 4 possess allergenic activity. Subsequently, IgG/IgE cross-binding was detected between Por t 4 and Lit v 4. Finally, structural analysis revealed that Por t 4 and Lit v 4 possess similar structural features. The peptide-inhibition experiments identified the presence of candidate linear cross-reactive B-cell epitopes, including B1 (AA 76-91), B2 (AA 111-125), and B3 (AA 132-147). Collectively, Por t 4 and Lit v 4 exhibited cross-binding; similar structural features and common cross-epitopes form the molecular foundation mediating their cross-recognition, and such cross-epitopes can serve as theoretical references for the diagnosis of cross-reactivity between different crustaceans.