ISOLATION AND CHARACTERIZATION OF PORCINE MANNAN-BINDING PROTEINS OF DIFFERENT SIZE AND ULTRASTRUCTURE

The authors report on the purification and characterization of mannan- binding proteins (MBP) isolated from porcine serum. The MBPs were puri fied by use of PEG precipitation, affinity chromatography on mannan-Se pharose, protein A- and anti-porcine IgM-Sepharose followed by gel fil tration. The MBP proteins were collagenase sensitive and showed gamma( 1)-gamma(2)-electrophoretic mobility. The MBP designated pMBP-28 had a molecular mass of 28 kDa when analysed on SDS-PAGE under reducing con ditions and eluted corresponding to a molecular mass of approximately 700 kDa on gel filtration chromatography. Electron micrographs of pMBP -28 revealed an oligomeric protein similar to rodent MBP-A and human M BP but with a predominance of penta- and hexameric molecules. Another protein designated pMBP-27 was composed of peptides of 27 kDa and had an M(r) of 300-350 kDa on gel filtration chromatography. Electron micr oscopy of pMBP-27 showed dimer and trimer molecules; the trimers witho ut distinct stalk regions. The N-terminal 26 (pMBP-27) and 24 (MBP-28) amino acid residues showed 54% and 58% identity with human MBP. pMBP- 28 showed a higher degree of sequence similarity to rat and mouse MBP- A (60% identity) than to mouse and rat MBP-C (41-45% identity). Both p MBPs exhibited Ca2+-dependent binding to D-mannose immobilized on agar ose but no significant binding to N-acetyl-D-glucosamine- or fucose-ag arose. The results further suggested the presence of a third pMBP whic h copurified with pMBP-27 but this protein was not sequenced.