A collectin-like protein from tunicates

Collectins are a sub-family of C-type lectins from mammals and birds that a re characterized by their collagen-like domains. The mammalian collectin, m annose binding lectin, has attracted considerable interest because it can a ctivate complement components via a lectin-mediated complement pathway that is independent of immunoglobulins. In this study, we have identified a cal cium-dependent lectin from the invertebrate (tunicate), Styela plicata, tha t bears substantial similarities to mammalian collectins. The tunicate lect in; which was isolated by carbohydrate affinity chromatography, has a reduc ed apparent molecular mass of 43 kDa. The 43 kDa reduced polypeptide appear ed as dimers, trimers and hexamers when analyzed by non-reducing and two-di mensional 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 s imilarities between the tunicate lectin and mammalian collectins, notably t he inclusion of a collagenous domain and a short, cysteine bearing N-termin al domain. The identification of a collectin-like protein in an invertebrat e such as S. plicata, which does not express immunoglobulin: indicates that lectin-mediated complement pathways may predate the origin of antibodies. (C) 2000 Elsevier Science Inc. All rights reserved.