PURIFICATION AND CHARACTERIZATION OF MANNAN-BINDING PROTEIN FROM MOUSE SERUM

Mouse mannan-binding protein (MBP) was identified in serum by its Ca2-dependent binding to mannan. On gel permeation chromatography, the pr otein eluted corresponding to a molecular weight of approximately 750 kDa. Analysed on SDS-PAGE under reducing conditions, the polypeptide s howed an apparent molecular weight of 28 kDa, while several high molec ular weight bands were seen under nonreducing conditions. The presence of collagen-like domains within the molecule was indicated by a high glycine content (14.9%) and substantiated by sensitivity to collagenas e. Rabbit anti-mouse MBP antisera were raised. The concentration of MB P in serum from normal mice was measured by rocket immunoelectrophores is and found to be from below 1 mu g/ml to 100 mu g/ml (average 50 mu g/ml, n = 60). The binding of mouse MBP to mannan could be inhibited b y mono- and disaccharides in the following order of potency: L-fucose > D-mannose > N-acetyl-D-glucosamine > maltose > D-mannoheptulose > D- glucose > N-acetyl-D-mannosamine much greater than lactose > D-galacto se much greater than N-acetyl-D-galactosamine. Mouse MBP was shown to activate the classical complement cascade after binding to mannan. The sequence of 14 NH2-terminal amino acid residues of the molecule showe d 93% identity to rat MBP-A and complete identity to the translated cD NA sequences for mouse MBP-A and mouse Ra-reactive factor component P2 8b (RaRF P28b) published previously. The amino acid composition of mou se MBP showed a high degree of homology to MBPs from other species and mouse RaRF P28b.