A C-type lectin (AjSJL-1) containing DPN/WVD motifs in Apostichopus japonicus recognizes multiple microbes

C-type lectins (CTLs) are a superfamily of Ca2+ dependent carbohydrate-recognition proteins with diversified functions ranging from embryonic development to immune defense. In the present study, a CTL containing only one CRD domain with new motifs Asp-Pro-Asn (DPN) and Trp-Val-Asp (WVD) in its Ca2+ binding site 2 (designated as AjSJL-1) was identified from sea cucumber Apostichopus japonicus. The deduced amino acid sequence of AjSJL-1 was homologous to CTLs from other animals with the identities ranging from 19 % to 28.4 %. The mRNA transcripts of AjSJL-1 were detected in all the examined tissues with varied abundance. The expression level of AjSJL-1 mRNA in coelomocyte was up-regulated significantly at 12 h after Vibrio splendidus challenge. The recombinant protein of AjSJL-1 (rAjSJL-1) displayed significant binding activity to lipopolysaccharide, peptidoglycan, mannose and D-galactose in a Ca2+-dependent manner. Moreover, rAjSJL-1 exhibited strong binding capability to V. splendidus but week to Staphylococcus aureus, Bifidobacterium breve, Pichia pastoris and Yarrowia lipolytica in the presence of Ca2+. These results collectively suggested that AjSJL-1 with new DPN/WVD motifs served as a pattern recognition receptor in sea cucumber with the capability to bind broad-spectrum microbes and initiate the immune response against invaders