Spätzle, a signaling molecule that interacts with pathogen-associated molecules and Toll-like receptor in Portunus trituberculatus

Spätzle is a crucial ligand for Toll-like receptor (TLR) that triggers the activation of TLR signal pathway in insects. In this study, open reading frames (ORFs) of two spätzles were cloned from Portunus trituberculatus (PtSpz1 and PtSpz2). Both of PtSpzs contained the typical cystine-knot domain of spätzle. Tissue distribution analysis showed that both of PtSpzs were predominantly expressed in the gills. Transcriptional levels of the two PtSpzs in hemocytes and gill rapidly increased at 3 h and 6 h post Vibrio alginolyticus challenge, respectively. The two PtSpzs could bind to several pathogen-associated molecules including lipopolysaccharide (LPS), peptidoglycan (PGN) and envelope proteins of white spot syndrome virus (WSSV). Moreover, the two PtSpzs could directly interact with the extracellular leucine-rich repeats (LRR) domain of TLR. This study revealed that spätzle could interact with pathogen-associated molecules and TLR of host, which may be two important steps for spätzle to deliver signals into host cells.