COLLECTIN IN A NONMAMMALIAN SPECIES - ISOLATION AND CHARACTERIZATION OF MANNAN-BINDING PROTEIN (MBP) FROM CHICKEN SERUM

A chicken serum lectin was isolated by affinity chromatography on TSK- 75 beads derivatized with the monosaccharide N-acetyl-D-mannosamine (M anNAc), Serum was applied to the column in a Ca2+-containing buffer an d proteins were eluted with EDTA, After recalcification, the eluate wa s passed through a new ManNAc-derivatized column, Bound proteins were eluted with 50 mM ManNAc, Anticarbohydrate antibodies present in the e luate were removed by passage through a rabbit anti-chicken immunoglob ulin derivatized column, and the lectin was further purified by ion-ex change chromatography and gel-permeation chromatography, The purified chicken lectin shows an overall structure similar to mammalian mannan- binding protein (MBP), SDS-PAGE revealed two polypeptides of M(r) 33 a nd 34 kDa (reduced) with identical sequence for the first 30 NH2-termi nal residues, The NH2-terminal sequence shows 43% identity with the hu man MBP. Like mammalian MBP, the polypeptides of the chicken lectin ar e degraded by treatment with collagenase, Residues 26-30 (G-L-P(OH)G-D ) are likely to represent the beginning of the collagenous region, Mob ilities on SDS-PAGE of the COOH-terminal collagenase-resistant fragmen t under reduced and nonreduced conditions indicate the presence of int rachain disulphide bonds, as are also found in mammalian MBP, Gel chro matography showed an intact mel. wt of 750 kDa, Binding of the chicken MBP to mannan was inhibited by monosaccharides in the following order of potency: ManNAc > L-fucose > mannose > N-acetylglucosamine, Other monosaccharides inhibited poorly or not at all, Chicken MBP, bound to mannan, activated the classical complement pathway in human serum, Ele ctron micrographs show structures and dimensions resembling human MBP. Overall, the results show that the purified lectin is the chicken hom ologue to mammalian MBP and indicate the presence of a MBP-like cleara nce system outside mammals.