Figure 8. Models of MuSK antibody inhibition of AChR clustering on myotubes.

(A) MuSK antibodies cover the ectodomain of MuSK and inhibit interactions with other scaffolding molecules required for AChR clustering, including myotube-associated component (MASC), rapsyn-associated transmembrane linker (RATL), and receptors for VVA-B4 and laminin. MASC is a hypothetical molecule that is required for agrin binding and the activation of MuSK. RATL, also a hypothetical molecule, mediates the association of rapsyn with the extracellular domain of MuSK. (B) MuSK antibodies induce the internalization of MuSK in the presence or absence of associated molecules. The lack of MuSK on the surfaces of myotubes inhibits the effects of scaffolding and AChR clustering.