Crosslinking of proteins in acetylcholine receptor-rich membranes from Torpedo californica: relation of 43-kD protein and Torpedo dystrophin to acetylcholine receptor.

We examined the spatial relation of 43-kD protein and Torpedo dystrophin, which are cytoplasmic peripheral membrane proteins in the nicotinic acetylcholine receptor (AChR)-rich membranes, to AChR. We used three kinds of the heterobifunctional crosslinking reagents to crosslink proteins in the AChR-rich membranes. Products crosslinked by SMPB (14.5 A span) including 43-kD protein and Torpedo dystrophin appeared at the tops of the stacking gels at the concentrations of 8.89 x 10(-5)M to 8.89 x 10(-3)M SMPB. High molecular weight materials (crosslinked products) increased with increasing concentrations of the crosslinker. On the other hand, band intensity of alpha, beta, and delta subunits of AChR remained unchanged up to a concentration of 2.67 x 10(-3)M SMPB, while the band of gamma subunit diminished at the same concentrations as did that of the 43-kD protein. Torpedo dystrophin was also crosslinked at the same concentrations as were effective for the 43-kD protein and gamma subunit. On the basis of these results, we conclude that the 43-kD protein is intimately associated with the gamma subunit of AChR and Torpedo dystrophin.