An inhibitor κB homologue from bay scallop Argopecten irradians

IκB is an important member of NF-κB pathway in the innate immune system. In the present study, the full-length cDNA sequence encoding IκB protein (designated AiIκB) was isolated from bay scallop Argopecten irradians. The complete sequence of AiIκB cDNA containing a 5′ untranslated region (UTR) of 237 bp, a 3′ UTR of 1023 bp with a poly (A) tail, and an open reading frame (ORF) of 1086 bp encoding a polypeptide of 361 amino acids with the predicted molecular weight of 39.9 kDa and theoretical isoelectric point of 4.7. Six ankyrin repeats which were necessary for specific binding to NF-κB and two potential phosphorylation sites responsible for IκB degradation were identified in the N-terminus of AiIκB. No PEST domain but a phosphorylation site motif (S357DSD360) was present at the C-terminus of AiIκB. Predicted three-dimensional structure of AiIκB shared high similarity with mammalian IκBα. Similarity and phylogenetic analysis revealed that AiIκB was clustered into IκBs from invertebrate. All these typical characteristics indicated that the AiIκB should be classified into IκB family proteins. Quantitative real-time RT-PCR was employed to assess the mRNA expression of AiIκB in various tissues and its temporal expression in haemocytes of scallops challenged with Listonella anguillarum. The mRNA transcript of AiIκB could be detected in all the examined tissues with highest expression level in hepatopancreas. Bacteria infection inhibited the transcription level of AiIκB. The results suggested the involvement of AiIκB in responses against bacterial infection and further highlighted its functional importance in the immune system of A. irradians.