Molecular isolation and expression analysis of hemocyanin isoform 2 of Macrobrachium rosenbergii.

Hemocyanin is a copper-bearing protein in the hemolymph of many arthropods and mollusks and functions as an oxygen transport and important nonspecific immune protein. In this study, cDNA of hemocyanin isoform 2 of Macrobrachium rosenbergii (MrHc2) was isolated and characterized. With a molecular mass of 77.3 kDa, MrHc2 contained three domains: hemocyanin-all-alpha, hemocyanin-copper-containing, and hemocyanin-immunoglobulin-like domains. Molecular phylogenetic analysis revealed that MrHc2 belongs to the γ-type subunit and is closely related to the hemocyanin subunit 1 of the palaemonid shrimp Macrobrachium nipponense. In addition, MrHc2 resided in a different clade of hemocyanin (MrHc) of M. rosenbergii (α-type subunit) and different subclades of hemocyanin proteins of penaeid shrimp. The mRNA transcript of MrHc2 was highly expressed in the hepatopancreas and weakly expressed in the gills, intestine, stomach, muscle, and hemocytes. Upon challenge with M. rosenbergii nodavirus (MrNV), the expression of MrHc2 was 1.96-, 2.93-, and 1.96-fold on days 3, 4, and 5, respectively, and then gradually declined to basal levels on day 7. This study suggests that MrHc2 plays an important role in the innate immune response of shrimp to MrNV.