A newly identified horseshoe crab lectin with binding specificity to O-antigen of bacterial lipopolysaccharides.
We identified a novel horseshoe crab hemocyte-derived lectin, which we named tachylectin-4. It has more potent hemagglutinating activity against human A-type erythrocytes than a previously identified hemocyte lectin with an affinity to N-acetylglucosamine, tachylectin-2. The purified tachylectin-4 is an oligomeric glycoprotein of 470 kDa, composed of subunits of 30 and 31.5 kDa. Ca2+ at 10 mM enhanced the hemagglutinating activity 4-fold, and the activity was inhibited by EDTA and o-phenanthroline. L-Fucose and N-acetylneuraminic acid at 100 mM completely inhibited the activity of tachylectin-4. The activity was also inhibited more strongly by bacterial S-type lipopolysaccharides (LPS) but not by R-type LPS lacking O-antigen. The most effective S-type LPS was from Escherichia coli O111:B4, and the minimum concentration required for inhibiting agglutination against human A-type erythrocytes (0.1 microg/ml) was 160-fold lower than those of S-type LPS from Salmonella minnesota. Therefore, colitose (3-deoxy-L-fucose), a unique sugar present in the O-antigen of E. coli O111:B4 with structural similarity to L-fucose, is the most probable candidate for a specific ligand of tachylectin-4. A cDNA coding for tachylectin-4 was isolated from a hemocyte cDNA library. The open reading frame of the 1344-base pair cDNA coded for the mature protein with 232 amino acids. There is no significant sequence similarity to any other known LPS-binding lectins, whereas tachylectin-4 is homologous to the NH2-terminal domain with unknown functions of Xenopus laevis pentraxin 1.
Saito
T
T
Department of Biology, Faculty of Science, Kyushu University, Fukuoka 812-82, Japan.
Hatada
M
M
Iwanaga
S
S
Kawabata
S
S
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002241:Carbohydrates / Q000494:pharmacology; D018076:DNA, Complementary / Q000737:chemistry / Q000302:isolation & purification; D006384:Hemagglutination / Q000187:drug effects; D006737:Horseshoe Crabs; D006801:Humans; D037102:Lectins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D019081:O Antigens / Q000378:metabolism*; D015183:Restriction Mapping; D016415:Sequence Alignment; D014982:Xenopus laevis
D002241:Carbohydrates; D018076:DNA, Complementary; C097500:L10 protein, Tachypleus tridentatus; D037102:Lectins; D019081:O Antigens; C425303:Tachypleus plasma lectin-1; C094130:lectin L6, Tachypleus tridentatus; C109533:tachylectin-4, horseshoe crab