Sequence analysis and bacterial agglutination of C-type lectin gene ScCTL-2 in Sinonovacula constricta

Abstract:

C-type lectins are a superfamily of Ca²⁺-dependent carbohydrate-binding proteins that play crucial roles in invertebrate immunity. A novel C-type lectin gene (ScCTL-2) was identified in razor clam Sinonovacula constricta. Sequence analysis showed that the full length ScCTL-2 contains a 1893 bp ORF encoding 630 amino acid polypeptide with four CTLD (C-type lectin domain) and a N-terminal transmembrane region. The special structure of ScCTL-2 protein revealed that ScCTL-2 is perhaps a new group of invertebrate C-type lectins. The ScCTL-2 was expressed in almost all tissues, with highest expression in hepatopancreas and the second highest expression in gill. Bacterial stimulation up-regulated ScCTL-2 expression in hemocytes. The spatial-and temporal-specific expression patterns of ScCTL-2 suggest it may be an immune-related gene in razor clam. Recombinant protein (rScCTL-2) displayed a broad bacterial agglutination spectrum, and the agglutinate activity was strictly Ca²⁺-dependent. It could agglutinate all the experimental bacteria only if Ca²⁺ existed. The results suggest ScCTL-2 is a novel gene possessing common immune characteristics of invertebrate C-type lectins.