A chitin binding protein from the kuruma shrimp Marsupenaeus japonicus involved in WSSV infection

The peritrophic membrane (PM) in the shrimp intestine serves as a critical physical barrier against pathogenic infections, highlighting the importance of maintaining PM integrity for resistance to White Spot Syndrome Virus (WSSV). In this study, we identified a chitin-binding protein (CBP) from Marsupenaeus japonicus (MjCBP). qRT-PCR analysis showed that the expression of MjCBP was downregulated upon WSSV challenge. RNA interference-mediated knockdown of MjCBP resulted in higher 7-day cumulative mortality in M. japonicus following WSSV infection, and elevated VP28 mRNA levels were detected in hemocytes of MjCBP-knockout shrimp compared to controls. Recombinant expression and purification of the first four CBDs (rMjCBP-F4) and the first CBD (rCBD1) revealed their ability to bind to N-Acetylglucosamine (NAG). Both rMjCBP-F4 and rCBD1 reduced cumulative mortality in WSSV-infected shrimp. Moreover, VP24 was shown to bind NAG, and NAG itself could decrease the cumulative mortality of WSSV-infected shrimp. Based on our findings, we hypothesize that WSSV employs VP24 to bind chitin, thereby anchoring to the PM and facilitating subsequent infection processes. In the shrimp intestine, we propose a dual protective mechanism by which MjCBP resists WSSV infection: (i) maintenance of PM integrity through chitin matrix stabilization, and (ii) competitive inhibition of VP24-chitin interactions critical for WSSV adsorption.