A unique primary structure, cDNA cloning and function of a galactose‐specific lectin from ascidian plasma

Abstract

The complete amino acid sequence of a galactose-specific lectin from the plasma of the ascidian Halocynthia roretzi has been determined by sequential Edman degradation analysis of peptide fragments derived by proteolytic fragmentation and chemical cleavage of the reductive S-pyridylethylated lectin. Peptide fragments were separated by reverse-phase HPLC. The N-terminal and C-terminal amino acid sequences were determined by Edman degradation and enzymatic digestion. The H. roretzi plasma lectin is a single-chain protein consisting of 327 amino acids and four disulfide bonds, one of which was found to be cross-linked intramolecularly. A comparison of the amino acid sequence of the H. roretzi plasma lectin with the sequences of other proteins reveals that the H. roretzi lectin has a structure consisting of a twice-repeated sequence, a fibrinogen-related sequence and a C-type lectin-homologous sequence. The above amino acid sequence was verified by cDNA cloning of this lectin. Three cDNA clones that have single ORFs encoding the lectin precursor were isolated from an H. roretzi hepatopancreas cDNA library. The deduced amino acid sequences in the three cDNA clones contain the same sequence of the mature lectin molecule and the same putative signal sequence. In addition, it was demonstrated that this lectin can enhance phagocytosis by H. roretzi hemocytes. Thus, the plasma lectin is constructed into an oligomer structure via intermolecular disulfide bonds and plays a role in the biological defense of H. roretzi as a defense molecule.

Intelectin gene from the grass carp Ctenopharyngodon idella: cDNA cloning, tissue expression, and immunohistochemical localization

“…In ascidian, the galactose-specific lectin functions as a phagocytosis-stimulating molecule, and may bind to and agglutinate invading foreign materials via galactose-containing sugars. In addition, this lectin may be capable of binding to haemocytes and stimulating the production of superoxide anions by haemocytes [12]. In human, the intelectin was suggested to be able to agglutinate ligands and bind to various pathogens containing galactofuranosyl residues [7].…”

Identification and Characterization of a Chitin-binding Protein Purified from Coelomic Fluid of the Lugworm Arenicola marina Defining a Novel Protein Sequence Family

“…Some lectins isolated from invertebrates show sequence homology to those isolated from vertebrates. Several lectins with carbohydrate-recognizing domains of C-type (calciumdependent) lectins have been found in tunicates, echinoderms, and arthropods (7)(8)(9)(10). Galectins (calcium-independent galactose-specific lectins) have been detected in annelids (11,12), nematodes (13)(14)(15), and sponges (16,17).…”

“…Fibrinogen-related domains (FReDs or FRePs) with lectin activity are found in mammalian lectins, such as the ficolins, and in invertebrates (18 -20). FReDs with lectin activity have been purified from the ascidian Halocynthia roretzi (9), the horseshoe crab Tachypleus tridentatus (21), and the snail Biomphalaria glabrata (22,23). The canonical FReD ligand-binding site (S1) in the horseshoe crab lectin tachylectin 5A, FIBCD1, and M-ficolin binds acetylated components in a calcium-and acetate-dependent manner (18).…”

An Ancient Lectin-Dependent Complement System in an Ascidian: Novel Lectin Isolated from the Plasma of the Solitary Ascidian, Halocynthia roretzi

“…As shown in Fig. 1, GBL is a major protein that binds to mannan-Sepharose, and an additional band of 40 kDa was identified as ascidian galactose-specific lectin (Gal-lectin) (30). Because MBL is mainly bound to mannose and GlcNAc, and we failed to isolate an MBL homologue that binds to mannose from ascidian hemolymph, we consider that GBL is the functional counterpart of MBL.…”