title: A collectin-like protein from tunicates.
abstract: Collectins are a sub-family of C-type lectins from mammals and birds that are characterized by their collagen-like domains. The mammalian collectin, mannose binding lectin, has attracted considerable interest because it can activate complement components via a lectin-mediated complement pathway that is independent of immunoglobulins. In this study, we have identified a calcium-dependent lectin from the invertebrate (tunicate), Styela plicata, that bears substantial similarities to mammalian collectins. The tunicate lectin, which was isolated by carbohydrate affinity chromatography, has a reduced apparent molecular mass of 43 kDa. The 43 kDa reduced polypeptide appeared as dimers, trimers and hexamers when analyzed by non-reducing and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis, while gel filtration suggested that the native form of the protein was a nonamer. Amino acid sequence and amino acid composition analysis revealed obvious similarities between the tunicate lectin and mammalian collectins, notably the inclusion of a collagenous domain and a short, cysteine bearing N-terminal domain. The identification of a collectin-like protein in an invertebrate such as S. plicata, which does not express immunoglobulin, indicates that lectin-mediated complement pathways may predate the origin of antibodies.
authors.affiliation: Department of Biological Sciences, Macquarie University, North Ryde, NSW, Australia.
authors.forename: S V
authors.initials: SV
authors.lastname: Nair
authors.forename: S
authors.initials: S
authors.lastname: Pearce
authors.forename: P L
authors.initials: PL
authors.lastname: Green
authors.forename: D
authors.initials: D
authors.lastname: Mahajan
authors.forename: R A
authors.initials: RA
authors.lastname: Newton
authors.forename: D A
authors.initials: DA
authors.lastname: Raftos
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis*; D000818:Animals; D002241:Carbohydrates / Q000737:chemistry; D002417:Cattle; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D006458:Hemolymph / Q000737:chemistry*; D006801:Humans; D037102:Lectins / Q000737:chemistry* / Q000378:metabolism*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000032:analysis; D011485:Protein Binding; D051381:Rats; D016415:Sequence Alignment; D014561:Urochordata / Q000737:chemistry* / Q000235:genetics
chemical_list: D000596:Amino Acids; D002241:Carbohydrates; D037102:Lectins; D010446:Peptide Fragments