A type III heat shock protein 40 regulates the expression of antimicrobial peptides and hemocyte phagocytosis in Portunus trituberculatus.

Heat shock protein 40 (HSP40) is molecular chaperone that participates in various abiotic and biotic stress. In this study, a type III HSP40 (PtHSP40-III) that mainly expresses in the thoracic ganglion of Portunus trituberculatus is identified. Despite PtHSP40-III shows relatively lower transcriptional level in hemocyte, its transcripts could be significantly induced by Vibrio alginolyticus. The recombinant protein of PtHSP40-III displays binding activity toward both Gram-negative bacteria and Gram-positive bacteria as well as pathogen-associated molecular patterns (PAMPs) such as lipopolysaccharide (LPS) and peptidoglycan (PGN). Meanwhile, PtHSP40-III could act as extracellular ligand for Toll-like receptor (TLR) via directly interacting with the leucine-rich repeats (LRR) domain of TLR. PtHSP40-III can promote the nuclear translocation of Dorsal as well as specifically regulate the expression of several antimicrobial peptides (AMPs) such as anti-lipopolysaccharide factor (ALF) and crustin. Furthermore, PtHSP40-III enhances the hemocyte phagocytosis against V. alginolyticus. These findings reveal that PtHSP40-III could serve as a signaling molecule to promote the expression of AMPs via TLR pathway and enhance hemocyte phagocytosis, which may be used as an immunoregulator to enhance the immunity of P. trituberculatus, thereby achieving disease prevention and control.