Detection of two distinct types of hemolymphatic prophenoloxidase and their differential responses in the black tiger shrimp, Penaeus monodon, upon infection by white spot syndrome virus

The present study demonstrates the existence of two distinct types of prophenoloxidases in the serum of the black tiger shrimp, Penaeus monodon, and their differential responses upon infection by white spot syndrome virus (WSSV). Empirical analyses performed using various activators (proteases and detergents) and phenolic substrates revealed that the anionic detergent, sodium dodecyl sulfate, was the best exogenous activator of serum prophenoloxidase (designated as prophenoloxidase-1), and the resulting phenoloxidase maximally oxidized an o-diphenolic substrate, dopamine (Km: 0.90 mM). A novel type of serum prophenoloxidase (designated as prophenoloxidase-2), with an intrinsic property of spontaneous conversion to phenoloxidase, was also detected, for the first time, in healthy shrimps. Interestingly, this phenoloxidase exhibited profound affinity for a monophenolic substrate tyramine (Km: 1.25 mM), and the level of prophenoloxidase-2 was 2.4-fold higher than that of prophenoloxidase-1. Strikingly, WSSV infection in shrimps inflicted a remarkable elevation in the level of prophenoloxidase-1 and concomitant depletion of prophenoloxidase-2, thereby demonstrating differential responses of these two distinct types of serum prophenoloxidases. The findings of this investigation implicate an important role of prophenoloxidase-2 in conferring antiviral state to shrimps.

► Two types of proPO detected in shrimp serum
► proPO-1 is SDS-activable.
► proPO-2 is predominant and spontaneously activable.
► They show differential response during WSSV infection.