Fucosylated hemocyanin regulates ER stress to enhance shrimp antibacterial immunity.

Invertebrates rely on post-translational modifications (PTMs) of immune effectors to regulate innate immunity, yet how hemocyanin fucosylation mediates intracellular antimicrobial signaling remains a critical knowledge gap in crustacean immunology. Although fucosylation enhances the in vitro antibacterial activity of Penaeus vannamei hemocyanin (PvHMC), its function in regulating intracellular stress-immune crosstalk remains unclear. Here, we identify a novel axis linking PvHMC fucosylation, endoplasmic reticulum stress (ERS), and antimicrobial peptide (AMP) production to bolster shrimp defense against Vibrio parahaemolyticus. Biotin pull-down coupled with LC-MS/MS revealed that highly fucosylated PvHMC preferentially associates with the ER chaperone PvBip, and this fucosylation-associated interaction was further supported by GST pull-down assays. Functional assays showed that High-Fuc-PvHMC enhanced a PvBip-PvXbp1s‑associated ER stress response and induced the transcription of key AMPs, including PvPEN2, PvLYZ2, PvALF2, and PvALF3. These effects were attenuated by the ER stress inhibitor 4-PBA. In vivo, High-Fuc-PvHMC reduced hemolymph Vibrio loads and improved shrimp survival after V. parahaemolyticus challenge, whereas reduced PvHMC fucosylation or ER stress inhibition weakened these protective effects. Collectively, our findings uncover an unrecognized intracellular role for hemocyanin whereby fucosylation enables PvHMC to modulate ERS via PvBip-PvXbp1s signaling for AMP-driven antibacterial immunity. This study expands the functional repertoire of this canonical oxygen-transport and immune effector protein, and provides key mechanistic insights into PTM-mediated immune regulation in crustaceans.