A photoaffinity ligand of the acetylcholine-binding site predominantly labels the region 179–207 of the α-subunit on native acetylcholine receptor from Torpedo marmorata

AbstractRegions of the Torpedo marmorata acetylcholine receptor (AChR) α-subunit involved in the binding of acetylcholine were probed with two different covalent ligands. The sulfhydryl-directed affinity reagent 4-(N-maleimido)phenyltrimethylammonium iodide labeled a single α-subunit cyanogen bromide fragment on the reduced AChR which was identified as α 179–207. The novel photoaffinity ligand p-(N,N-dimethylamino)-benzenediazonium fluoroborate, on the other hand, labeled three distinct α-chain cyanogen bromide fragments on the unmodified AChR in a carbamylcholine-protectable manner. The major radiolabeled species was purified and identified by sequence analysis as α 179–207. The acetylcholine-binding site on the native AChR may thus involve several distinct portions of the α-chain, with the region α 179–207 making a major contribution to the site