[Agrin acts at the nerve-muscle synapse in the glomerular basal membrane and on T-lymphocytes]

The role of agrin, a large proteoglycan containing heparan-sulfate in the synaptic cleft, has been elucidated in recent years. The molecule released from the motor-neuron endplate, binds to a complex of 2 adjacent receptors at the post-synaptic myotube surface. It binds first to MASC (myotube associated specific component) and thus triggers a signal at the MuSK (muscle-specific kinase) receptor that generates tyrosine phosphorylation. A cascade of further responses of RATL and rapsyn leads to the aggregation of acetylcholine receptors. Lately, agrin is also implicated as a sulfated proteoglycan in the glomerular basement membrane as a barrier preventing albuminuria. It is also hypothesized that agrin functions at the surface of activated T-lymphocytes as a part of the recognition process between antigen-presenting-lymphocytes and responding T cells.