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Peritrophic membrane (PM) refers to a vital physical barrier enabling shrimp to resist pathogen invasion. It primarily consists of chitin and proteins, mostly chitin-binding protein (CBP). CBPs have been identified from microorganisms to higher organisms. In the present study, a CBP, designated Mj CBP, was reported from Marsupenaeus japonicus. The open reading frame of MjCBP was 1854 bp, encoding a protein with 618 amino acids (MH544098). To be specific, the theoretical pI and molecular mass of mature MjCBP reached 5.43 and 66064.00 Da, respectively. MjCBP consisted of seven type Ⅱ chitin-binding domains (ChtB D2), which was up-regulated after being challenged with Vibrio anguillarum and then agglutinating several bacteria. In addition, MjCBP and the first chitin-binding domain (CBD1) could bind to several Gram-positive and Gram-negative bacteria via the binding process to lipopolysaccharides and peptidoglycans, whereas CBD1 was not capable of agglutinating bacteria. Moreover, the anterior and posterior segments of CBD1 were synthesized in vitro, and the posterior segment could bind to lipopolysaccharides. However, both segments fail to agglutinate bacteria. Furthermore, MjCBP and CBD1 facilitated the clearance of V. anguillarum in vivo, and the silencing of MjCBP via RNA interference reduced the ability of bacterial clearance. As revealed from the mentioned results, MjCBP acts as an opsonin or pattern recognition receptor to achieve antibacterial immune response in shrimp. • MjCBP can agglutinate several Gram-positive and -negative bacteria. • MjCBP and CBD1 can bind to several Gram-positive and -negative bacteria. • MjCBP and CBD1 can bind to lipteihcoicacid, lipopolysaccharides and peptidoglycans. • Recombinant MjCBP and CBD1 can enhance the clearance of V. anguillarum in vivo. • MjCBP konckdown decreased V. anguillarum clearance ability. [ABSTRACT FROM AUTHOR]

L-type lectins (LTLs) belong to the lectin family and are characterized by a conserved structural motif in their carbohydrate recognition domain. LTLs are homologous to leguminous lectins. In this study, we identified and functionally characterized an LTL from kuruma shrimp Marsupenaeus japonicus. We designated this LTL as Mj LTL2. Mj LTL2 contains a signal peptide, a Lectin_leg domain, a coiled coil, and transmembrane domain. Mj LTL2 is distributed in hemocytes, heart, hepatopancreas, gill, stomach, and intestine; higher expression levels are seen in hemocytes and the hepatopancreas than in other tissues. Mj LTL2 was upregulated following challenge of shrimp with Vibrio anguillarum and white spot syndrome virus (WSSV). Mj LTL2 can agglutinate several bacteria without Ca2+. In addition, Mj LTL2 could bind to several Gram-positive and -negative bacteria by binding to their lipopolysaccharide and peptidoglycan. However, Mj LTL2 could not enhance the clearance of V. anguillarum in vivo. In the presence of WSSV infection, Mj LTL2 knockdown by RNA interference resulted in a 7-day lower cumulative mortality of M. japonicus. Moreover, less VP19, VP24, VP26, and VP2 8 mRNAs were extracted from the hemocytes of Mj LTL2 knockdown shrimp than from the control. These results suggest that Mj LTL2 is involved in immune responses in shrimp. • Mj LTL2 could agglutinate several Gram-positive and -negative bacteria. • Mj LTL2 could bind to several Gram-positive and -negative bacteria. • Mj LTL2 could bind to lipopolysaccharide and peptidoglycan. • MjLTL2 knockdown resulted in a lower cumulative mortality of M. japonicus in the presence of WSSV infection. • MjLTL2 knockdown resulted in a lower VP19 , VP24 , VP26 , and VP28 expression levels. [ABSTRACT FROM AUTHOR]