The structure of a prophenoloxidase (PPO) from Anopheles gambiae provides new insights into the mechanism of PPO activation

摘要: Phenoloxidase (PO)-catalyzed melanization is a universal defense mechanism of insects against pathogenic and parasitic infections. In mosquitos such as Anopheles gambiae, melanotic encapsulation resistance certain parasites that cause malaria filariasis. PO initially synthesized by hemocytes released into hemolymph inactive prophenoloxidase (PPO), which activated serine protease cascade upon recognition foreign invaders. The mechanisms PPO activation catalysis have been elusive. Herein, we report the crystal structure PPO8 from A. gambiae at 2.6 A resolution. forms homodimer with each subunit displaying classical type III di-copper active center. Our molecular docking mutagenesis studies revealed new substrate-binding site Glu364 catalytic residue responsible for deprotonation mono- di-phenolic substrates. Mutation severely impaired both monophenol hydroxylase diphenoloxidase activities AgPPO8. data suggested newly identified pocket actual catalysis, could be achieved without withdrawing conserved phenylalanine was previously deemed substrate ‘placeholder’. We present structural functional mosquito PPO. results novel key enzymatic activities. offered model level, differs canonical demands blocking site. This study provides insights PO.