Novel function of QM protein of shrimp (Penaeus japonicus) in regulation of phenol oxidase activity by interaction with hemocyanin.

Since it was proposed to be a tumor suppressor in 1991, the QM protein has attracted intensive studies in plants, animals and fungi. Up to date, however, the function of QM protein remains unknown. In this investigation, it was found that the shrimp QM gene (designated as PjQM) was significantly up-regulated in virus- resistant shrimp, suggesting that the PjQM was involved in shrimp immunity. The GST pull-down assays showed that the PjQM protein interacted with shrimp hemocyanin and myosin, indicating that the PjQM protein might participate in prophenoloxidation (proPO) activation system of shrimp immunity. As revealed by RNAi assays, it was demonstrated for the first time that the QM protein could regulate the activity of phenol oxidase, a key enzyme in the proPO activation system of invertebrate immunity. This discovery showed a novel aspect of QM protein in arthropod immune response, which contributed a better understanding to the still poorly understood molecular events involved in innate immunity of arthropods.