FUNCTIONAL TOPOGRAPHY OF MYELIN-ASSOCIATED GLYCOPROTEIN .2. MAPPING OF DOMAINS ON MOLECULAR FRAGMENTS

The myelin-associated glycoprotein (MAG), an adhesion molecule of the immunoglobulin (Ig) superfamily with five Ig-like domains, was investi gated with regard to its binding site(s) for the neuronal cell surface , collagen I, and heparin, using a panel of new monoclonal antibodies and cyanogen bromide cleavage fragments of MAG, All antibodies generat ed competed with each other for binding to MAG, indicating that they r eacted with identical or closely related epitopes, Mapping of the reac tive epitopes on recombinant deletion fragments of MAG expressed by Ch inese hamster ovary (CHO) fibroblasts showed reactivity of monoclonal antibody 513 with domains I, II, and III, comprising the amino-termina l end of the extracellular domain, Monoclonal antibody 15 recognized d omain III only, Binding of MAG-containing liposomes to neurons was blo cked by antibodies 15 and 513, Cyanogen bromide (CNBr) fragments of do mains I, II, and III bound to collagen type I under isotonic buffer co nditions, CNBr fragments containing domains I and II were involved in binding to heparin, These observations suggest that domain III may be important for binding to the neuronal cell surface receptor for MAG, w hile domains I, II, and III interact with collagen type I and domains II and III with heparin. (C) 1995 Wiley-Liss, Inc.