Cloning and characterization of a sialic acid binding lectins (SABL) from Manila clam Venerupis philippinarum

Sialic acid binding lectin (SABL) is a member of immunoglobulin-like lectins family that are thought to promote cell–cell interactions and regulate the functions of cells in the innate and adaptive immune systems through glycan recognition. In the present study, the full-length cDNA of SABL was identified from Manila clam Venerupis philippinarum (denoted as VpSABL) by cDNA library and RACE approaches. The cDNA of VpSABL consisted of a 5′terminal untranslated region (UTR) of 62 bp, a 3′ UTR of 354 bp with a poly (A) tail, and an open reading frame (ORF) of 588 bp encoding a polypeptide of 195 amino acids with a typical C1q domain in the C-terminus. Multiple alignment analysis indicated that the deduced amino acid of VpSABL shared higher positive to other SABLs and C1q-contained proteins and should be adopted typical 10 β-strand jelly-roll folding topology common to all C1q-TNF family. Spatial expression analysis indicated that mRNA transcript of VpSABL was predominantly detectable in tissues of mantle, hepatopancreas and gill, and to a lesser degree in the tissues of muscle and haemocytes. After challenged by Vibrio anguillarum, the mRNA level of VpSABL in overall haemocytes population was recorded by quantitative real-time RT-PCR. VpSABL mRNA was down-regulated in the first 24 h post-infection. Then, the expression level increased to the peak at 72 h and recovered to the original level at 96 h. All these results indicated that VpSABL was involved in the immune response against microbe infection and might be contributed to the recognition of bacterial pathogens.