Purification, composition, and structure of macrophage adhesion molecule

Publisher Website
Google Scholar
Abstract
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 .apprx. 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 .apprx. 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.