title: Horseshoe crab acetyl group-recognizing lectins involved in innate immunity are structurally related to fibrinogen.
abstract: We have characterized and cloned newly isolated lectins from hemolymph plasma of the horseshoe crab Tachypleus tridentatus, which we named tachylectins 5A and 5B (TLs-5). TLs-5 agglutinated all types of human erythrocytes and Gram-positive and Gram-negative bacteria. TLs-5 specifically recognize acetyl group-containing substances including noncarbohydrates; the acetyl group is required and is sufficient for recognition. TLs-5 enhanced the antimicrobial activity of a horseshoe crab-derived big defensin. cDNA sequences of TLs-5 indicated that they consist of a short N-terminal Cys-containing segment and a C-terminal fibrinogen-like domain with the highest sequence identity (51%) to that of mammalian ficolins. TLs-5, however, lack the collagenous domain found in a kind of "bouquet arrangement" of ficolins and collectins. Electron microscopy revealed that TLs-5 form two- to four-bladed propeller structures. The horseshoe crab is equipped with a unique functional homologue of vertebrate fibrinogen, coagulogen, as the target protein of the clotting cascade. Our observations clearly show that the horseshoe crab has fibrinogen-related molecules in hemolymph plasma and that they function as nonself-recognizing lectins. An ancestor of fibrinogen may have functioned as a nonself-recognizing protein.
authors.affiliation: Department of Biology, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Gokudan
authors.forename: T
authors.initials: T
authors.lastname: Muta
authors.forename: R
authors.initials: R
authors.lastname: Tsuda
authors.forename: K
authors.initials: K
authors.lastname: Koori
authors.forename: T
authors.initials: T
authors.lastname: Kawahara
authors.forename: N
authors.initials: N
authors.lastname: Seki
authors.forename: Y
authors.initials: Y
authors.lastname: Mizunoe
authors.forename: S N
authors.initials: SN
authors.lastname: Wai
authors.forename: S
authors.initials: S
authors.lastname: Iwanaga
authors.forename: S
authors.initials: S
authors.lastname: Kawabata
mesh_terms: D000017:ABO Blood-Group System; D000595:Amino Acid Sequence; D000818:Animals; D001798:Blood Proteins / Q000737:chemistry* / Q000276:immunology* / Q000494:pharmacology; D002241:Carbohydrates; D018076:DNA, Complementary; D004912:Erythrocytes / Q000276:immunology*; D004926:Escherichia coli / Q000187:drug effects; D005340:Fibrinogen / Q000737:chemistry*; D006386:Hemagglutination Tests; D006737:Horseshoe Crabs / Q000276:immunology*; D006801:Humans; D007700:Kinetics; D037102:Lectins / Q000737:chemistry* / Q000276:immunology* / Q000494:pharmacology; D008322:Mammals; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D012475:Salmonella / Q000187:drug effects; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D000017:ABO Blood-Group System; D001798:Blood Proteins; D002241:Carbohydrates; D018076:DNA, Complementary; D037102:Lectins; D010446:Peptide Fragments; C121518:TL-5A protein, Tachypleus tridentatus; C121519:TL-5B protein, Tachypleus tridentatus; D005340:Fibrinogen