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 n euromuscular junction and have been implicated in the differentiation of th e 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 ep itopes, CT1 and CT2, both stain synaptic sites on skeletal muscle fibers. H owever, CT1 selectively stains nerve terminal, whereas CT2 selectively stai ns the postsynaptic apparatus. Likewise, CT1 and CT2 selectively stain moto neuron-like and muscle cell lines, respectively. Using the cell lines, we i dentify distinct CT1- and CT2-reactive glycolipids and glycoproteins. Final ly, we show that GalNAc modulates the adhesion of motoneuron-like cells to recombinant fragments of a synaptic cleft component, laminin beta 2. Togeth er, these results show that pre- as well as postsynaptic membranes bear and are affected by distinct but related synapse-specific carbohydrates.