Characterization Of Hemocyanin Subunits From Marsupenaeus Japonicus And Their Involvement In Antiviral Defense

Hemocyanin occurs in several classes: Crustacea, Myriapoda, Merostomata and Arachnida. As the main protein component of hemolymph, hemocyanin typically represents up to 95% of the total amount of protein. Hepatopancreas has been shown to be the site of hemocyanin synthesis. Hemocyanin (hexamer form) is freely dissolved in shrimp hemolymph and mainly responsible for oxygen transport.In addition to their primary function as an oxygen carrier for many arthropods, it has been suggested that hemocyanins would be multifunctional proteins involved in physiological processes such as osmoregulation, protein storage or enzymatic activities. Although it was also found to function in innate immunity of many arthropods and mollusks, involvement of hemocyanin in antiviral defense is seldom reported. In this study, we found that purified shrimp hemocyanin significantly delayed the infection of shrimp white spot syndrome virus (WSSV) in vivo.Two hemocyanin subunit genes (PjHcY and PjHcL) were thus cloned from Marsupenaeus japonicus. Interestingly, the effect of viral infection on the expression of these two subunits was different. PjHcL mRNA was strongly induced by WSSV infection while PjHcY varied little. Moreover, in WSSV-resistant shrimp, a much more significant up-regulation was found on the expression of PjHcL comparing with PjHcY. These findings not only reveal an important role of shrimp hemocyanin in antiviral defense, but also suggest a possible difference between its subunits in shrimp innate immunity.