Topographical Analysis of the Torpedo Marmorata Acetylcholine Receptor by Energy Transfer Photoaffinity Labeling Using Aryldiazonium Derivatives
The acetylcholine and the non competitive blockers binding sites of the native, membrane-bound acetylcholine receptor from Torpedo Marmorata were covalently photo-labeled by aryldiazonium derivatives.These derivatives are shown to be ligands of both sites and to be selectively activated once bound by an energy transfer reaction involving tryptophan residue(s) of the protein.The labeled subunits were analysed. The a subunit of the acetylcholine receptor is essentially involved into the agonist binding site while each of the five subunits is part of the non competitive blockers binding area. The a-chain residues Trp-149, Tyr-190, Cys-192, Cys-193 and an unidentified residue in the 80–105 segment are labeled in an agonist protectable manner, suggesting that they belong to the agonist binding site.These amino-acids are located in the large amino-terminal hydrophilic domain of the α-subunit primary structure and may lie in close proximity on the native receptor.
KeywordsCyanogen Bromide Competitive Antagonist Label Amino Acid Photoaffinity Label Desensitize State
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