25] Mannose/N-acetylglucosamine-binding proteins from mammalian sera

Abstract

Sera from various mammals are known to contain a binding protein that can recognize and bind mannose and N-acetylglucosamine residues. This protein—called “serum mannan-binding protein,” (S-MBP)—has been shown to activate the complement system through the classical pathway. Bovine serum is known to contain a unique protein, called conglutinin, that binds to a complement component but does not activate the complement system. Conglutinin is also shown to be a carbohydrate-binding protein specific for N-acetylglucosamine. This chapter is concerned with isolation of S-MBP from human, rat, rabbit, and bovine sera as well as isolation of conglutinin from bovine serum. The binding properties of conglutinin and MBP are generally similar. However, there are important differences in their binding specificity. Conglutinin is inhibited almost exclusively by N-acetylglucosamine both in binding to 125 I-labeled mannan and in the conglutination reaction, while MBP is potently inhibited by mannose as well as N-acetylglucosamine.