Multiplicity, structures, and endocrine and exocrine natures of eel fucose-binding lectins.
Lectins, a group of proteins that bind to cell surface carbohydrates and play important roles in innate immunity, are widely used experimentally to distinguish cell types and to induce cell proliferation. Eel serum lectins have been useful as anti-H hemagglutinins and also in lectin histochemistry as fucose-binding lectins (fucolectins), but their structures have not been determined. Here we report the primary structures and the sites of synthesis of eel fucolectins. Eel serum fucolectins were separated by two-dimensional gel electrophoresis and sequenced. cDNA cloning, based on the amino acid sequence information, and Northern blot analysis indicated that 1) the fucose-binding lectins are secretory proteins and have unique structures among the lectins, exhibiting only weak similarities to frog pentraxin, horseshoe crab tachylectin-4, and fly fw protein; 2) there are at least seven closely related members; and 3) their messages are abundantly expressed in the liver and in significant levels in the gill and intestine. The lectin-producing hepatic cells were identified by immunostaining; in the gill, exocrine mucous cells were stained, suggesting that serum fucolectins derive from the liver. Using primary culture of eel hepatocytes, the message levels were shown to be increased by lipopolysaccharide, suggesting a role for fucolectins in host defense. SDS-polyacrylamide gel electrophoresis analysis showed that eel fucolectins have a SDS-resistant tetrameric structure consisting of two disulfide-linked dimers.
PubMed ID: 10924498
Article link: J Biol Chem.
Genes referenced: fucolectin ptx pxn
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|Figure 4 Amino acid sequence alignment of eel fucolectins and other related proteins. The black shading in upper seven lines indicates the residues conserved among eel fucolectins (eFL-1–7). Similarities between eel fucolectins and the related proteins tachylectin-4 (TL-4, accession no. AB005542), Xenopus pentraxin 1 (XL-PXN, L19881), and Drosophila furrowed protein (D-FW, accession no. AE003487-48; see “Discussion”) and its homologue (D-CG9095, accession no.AE003498-6) are represented by the gray boxes in lower four lines. Gaps are introduced to obtain maximal sequence alignment. Numbers to the left andright refer to the first and last amino acid residues on the lines. eFL-1–3 are isolated from the liver and eFL-4–7, from the gill. A data base search also identified a partial sequence of a rainbow trout homologue with a 63% similarity (T23111) in the GenBank™ Expressed Sequence Tag data base. The BLAST and MOTIF programs were used to search the GenBank™ data base at the NCBI web site.|
|Figure 10 Domain structures of proteins containing a fucolectin domain. In addition to Xenopus pentraxin 1 (XP-PXN), which has a fucolectin domain in its N terminus (23), a homology search using the complete Drosophila genome sequence data, compiled recently by Celera Genomics (25), identified a fusion protein (D-FW) comprising fucolectin and selectin domains. Pentraxins are a family of acute phase reactants with a lectin domain. Selectins are adhesion molecules with a lectin domain, several complement repeats, and a transmembrane span. Numbers on theright indicate the total amino acid residue number. For the fucolectin-like sequences of these chimeric proteins, see Fig. 4.eFL, eel fucolectin; FL, fucolectin domain;D-FW, Drosophila furrowed protein; TM, transmembrane span.|