Distinct structures and functions of related pre- and postsynaptic carbohydrates at the mammalian neuromuscular junction

Carbohydrates that terminate in a-linked N-acetylgalactosamine (beta GalNAc) residues are concentrated in the postsynaptic apparatus of the skeletal neuromuscular junction and have been implicated in the differentiation of the postsynaptic membrane. We now report that distinct synapse-specific beta GalNAc-containing carbohydrates are associated with motor nerve terminals. Two monoclonal antibodies that recognize distinct beta GalNAc-containing epitopes, CT1 and CT2, both stain synaptic sites on skeletal muscle fibers. However, CT1 selectively stains nerve terminal, whereas CT2 selectively stains the postsynaptic apparatus. Likewise, CT1 and CT2 selectively stain motoneuron-like and muscle cell lines, respectively. Using the cell lines, we identify distinct CT1- and CT2-reactive glycolipids and glycoproteins. Finally, we show that GalNAc modulates the adhesion of motoneuron-like cells to recombinant fragments of a synaptic cleft component, laminin beta 2. Together, these results show that pre- as well as postsynaptic membranes bear and are affected by distinct but related synapse-specific carbohydrates.