CONFORMATION AND FUNCTION OF THE N-LINKED GLYCAN IN THE ADHESION DOMAIN OF HUMAN CD2

The adhesion domain of human CD2 bears a single N-linked carbohydrate. The solution structure of a fragment of CD2 containing the covalently bound high-mannose N-glycan [-(N-acetylglucosamine)(2)-(mannose)5-8] was solved by nuclear magnetic resonance. The stem and two of three br anches of the carbohydrate structure are well defined and the mobility of proximal glycan residues is restricted. Mutagenesis of all residue s in the vicinity of the glycan suggests that the glycan is not a comp onent of the CD2-CD58 interface; rather, the carbohydrate stabilizes t he protein fold by counterbalancing an unfavorable clustering of five positive charges centered about lysine-61 of CD2.