F-type lectin from the sea bass (Dicentrarchus labrax): Purification, cDNA cloning, tissue expression and localization, and opsonic activity

Abstract

Recently described biochemical and structural aspects of fucose-binding lectins from the European eel (Anguilla anguilla) and striped bass (Morone saxatilis) led to the identification of a novel lectin family ("F-type" lectins) characterized by a unique sequence motif and a characteristic structural fold. The F-type fold is shared not only with other members of this lectin family, but also with apparently unrelated proteins ranging from prokaryotes to vertebrates. Here we describe the purification, biochemical and molecular properties, and the opsonic activity of an F-type lectin (DlFBL) isolated from sea bass (Dicentrarchus labrax) serum. DlFBL exhibits two tandemly arranged carbohydrate-recognition domains that display the F-type sequence motif. In situ hybridization and immunohistochemical analysis revealed that DlFBL is specifically expressed and localized in hepatocytes and intestinal cells. Exposure of formalin-killed Escherichia coli to DlFBL enhanced their phagocytosis by D. labrax peritoneal macrophages relative to the unexposed controls, suggesting that DlFBL may function as an opsonin in plasma and intestinal mucus.

Evolution and Immune Function of Fish Lectins

“…20 The multiple duplicate tandem homologues present in modern teleost orders appear to be the product of independent duplications. 20 Previously, we reported the purification of sea bass (DlFBL) and gilt head bream (SauFBL) serum fucose-binding lectins, 23,30,31 and we also demonstrated that SauFBL displays epitopes recognized by anti-DlFBL-specific antibodies. Furthermore, based on the DlFBL cDNA sequence, we showed that it is a bona fide FTL, as it shares carbohydrate specificity and biochemical properties with other well-characterized FTLs.…”

“…Furthermore, based on the DlFBL cDNA sequence, we showed that it is a bona fide FTL, as it shares carbohydrate specificity and biochemical properties with other well-characterized FTLs. 23 FTLs have also been described in the shark To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print.…”

“…[17][18][19][20] Furthermore, some lectin families unique to fish, such as the RBLs have also been identified in eggs and embryos 21 but are also present in the serum. 22 Lectins can exert opsonic activity 7,9,23 or enhance respiratory burst and bactericidal activity of phagocytic cells. 19,24,25 Considerable heterogeneity has been identified in the FTL of the Japanese eel 15 that exists in various isoforms.…”

“…20 28 We proposed that fish F-lectins mediate immune defense responses both in the bloodstream 20,28,29 and the intestinal mucus. 20,23,30,31 They are expressed in larval and juvenile tissues and are also stored in eggs. 33 The scarcity of bacteria possessing FTL CRDs suggests that it may have been acquired through horizontal transfer from metazoans.…”

“…28 FTLs (Table 18.2) have been identified in the serum from fish. 20 While the European eel (A. anguilla) agglutinin (AAA) 20,28 possesses a single CRD, those from the striped bass (Morone saxatilis), MsFBP32, 20 the sea bass (D. labrax), DlFBL,23,30 and the sea bream (Sparus aurata), SauFBL, 31 exhibits two tandemly arrayed (N-and C-terminal) CRDs. The structure of MsFBP32 in complex with l-fucose revealed a trimeric organization with two globular opposite halves containing respectively the N-CRDs and the C-CRDs.…”