Identification and characterization of glycosylation sites on Litopenaeus vannamei hemocyanin
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The respiratory glycoprotein hemocyanin has been implicated in immune-related functions. Using lectin blotting, we show that the binding of shrimp ( Litopenaeus vannamei ) hemocyanin to concanavalin A decreases markedly with O-glycosidase treatment but not with PNGase F. Twelve O-glycosylation sites, three on the large hemocyanin subunit and nine on the small hemocyanin subunit (HMCs), were identified by LC-MS/MS. Importantly, when the glycosylation sites at Thr-537, Ser-539, and Thr-542 on the C terminus of HMCs were replaced with alanine, the resultant mutant hemocyanin had reduced carbohydrate content, coupled with a fourfold reduction in bacterial agglutination and 0.2-fold reduction in antibacterial activities toward Vibrio parahaemolyticus and Staphylococcus aureus . These results suggest that the glycosylation sites on shrimp hemocyanin are closely related to its immunological functions.