Spectrins at the Neuromuscular Junction
Our studies of a model for the postsynaptic membrane of the neuromuscular junction show that the acetylcholine receptors are bound to a spectrin-rich membrane-associated cytoskeleton (membrane skeleton). This skeleton is unusual, however, because it contains several giant members of the spectrin superfamily, including dystrophin, utrophin and ACF7 (a.k.a. MACF, trabeculin). We have found that ACF7 binds directly to rapsyn, a receptor-associated protein required for aggregating receptors at the developing neuromuscular junction. These results suggest that rapsyn links receptors directly to a cytoskeleton comprised in part of ACF7. An example of the close association of ACF7 and the receptors is shown below. Our most recent studies have focused on how these related molecules interact with each other to form a membrane skeleton and with the receptors to anchor them in the postsynaptic region.