Purification, composition, and structure of macrophage adhesion molecule.
Macrophage adhesion molecule (MAM) is a surface heterodimer consisting of the trypsin- and plasmin-sensitive glycopeptide gp160 (MAM-alpha) and the glycopeptide gp93 (MAM-beta). MAM, which is the guinea pig analogue of Mo1 and Mac-1, was purified from detergent lysates of peritoneal neutrophils by lentil lectin chromatography and M2-antibody chromatography. The pure heterodimer molecule was dissociated by acidic conditions (pH 3.5), and MAM-alpha and MAM-beta were separated by M7-antibody chromatography. MAM-beta is an approximately 640 amino acid residue polypeptide with exceptionally high cysteine content. At 7.2 residues per 100 amino acids, Cys/2 of MAM-beta is more than 3 times the mean for 200 purified proteins. Reactivity with six beta-subunit-specific monoclonal antibodies recognizing at least four epitopes demonstrated that intrapeptide disulfide bonds are required to maintain the structure of MAM-beta. All six antibodies failed to react when MAM-beta was treated with reducing agents. MAM-beta is 18% carbohydrate; the major monosaccharides are mannose, N-acetylglucosamine, galactose, and sialic acid. MAM-beta is estimated to contain five to six N-linked carbohydrate units. MAM-alpha is an approximately 1100-residue polypeptide with lower Cys/2 content (2.0 residues per 100 amino acid residues). MAM-alpha is 21% carbohydrate. The major monosaccharides are mannose, N-acetylglucosamine, galactose, and sialic acid; the mannose content is higher in MAM-alpha than MAM-beta. MAM-alpha is estimated to contain 12 N-linked carbohydrate units.
Remold-O'Donnell
E
E
Center for Blood Research, Boston, Massachusetts 02115.
Savage
B
B
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D000954:Antigens, Surface / Q000302:isolation & purification*; D002241:Carbohydrates / Q000032:analysis; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules; D002846:Chromatography, Affinity; D006168:Guinea Pigs; D008264:Macrophages / Q000276:immunology*; D009504:Neutrophils / Q000276:immunology
D000596:Amino Acids; D000954:Antigens, Surface; D002241:Carbohydrates; D015815:Cell Adhesion Molecules