Rapsyn

A neurally derived signaling protein, agrin, acts through a receptor tyrosine kinase, MuSK, in the formation of the specialized postsynaptic endplate by interaction with rapsyn. Thus, MuSK-rapsyn interactions are critical in forming the local scaffold for postsynaptic components in the motor endplate [43,44]. 

Nghiem HO, Bettendorff L, and Changeux JP (2000) Specific phosphorylation ofTorpedo 43K rapsyn by endogenous kinase(s) with thiamine triphosphate as the phosphate donor. FASEB Journal 14, 543-54. 

Fukushima T, Ohta M, Tanaka K, Kaneko S-Y, Maeda T, Sasaki A (2004) Niacin metabolism and Parkinson s disease. Asia Pac J Clin Nutr 13(Suppl) S176 Gautam M, Noakes PG, Mudd J, Nichol M, Chu GC, Sanes JR, Merlie JP (1995) Failure of post-synaptic specialization to develop at neuromuscular junctions of rapsyn-deficient mice. Nature 377(6546) 232-236... 

The large proportion of mass (—70%)that is not within the membrane, and shapes these vestibules is also needed for other purposes, such as making the (complex) ACh-binding pockets, and providing sites of attachment for regulatory molecules and other proteins (such as rapsyn) that are concentrated at the synapse. 

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