title: Acetylcholine mustard labels the binding site aspartate in muscarinic acetylcholine receptors.
abstract: Acetylcholine mustard (AChM) is an analogue of acetylcholine (ACh) in which the onium headgroup is replaced by a chemically reactive aziridinium moiety. AChM aziridinium has agonist activity, but, having bound, reacts with and blocks the muscarinic receptor (mAChR) binding site. Purified mAChRs from rat forebrain have been specifically labeled with [3H]AChM. The linkage formed is cleaved by hydroxylamine, is found within cyanogen bromide (CNBr) peptides with molecular masses of approximately 2.4 and 3.9 kDa, and is close to a disulfide-bonded cysteine. Edman degradation reveals a site of label attachment 26 residues C-terminal to a CNBr cleavage site. As in the case of the alkylating antagonist analogue [3H]propylbenzilylcholine mustard, these findings indicate that a conserved aspartic acid residue in transmembrane helix 3 of the mAChRs, corresponding to Asp-105 (m1 sequence), is the site of label attachment.
authors.affiliation: Division of Physical Biochemistry, Medical Research Council National Institute for Medical Research, London, United Kingdom.
authors.forename: T A
authors.initials: TA
authors.lastname: Spalding
authors.forename: N J
authors.initials: NJ
authors.lastname: Birdsall
authors.forename: C A
authors.initials: CA
authors.lastname: Curtis
authors.forename: E C
authors.initials: EC
authors.lastname: Hulme
mesh_terms: D000109:Acetylcholine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D000478:Alkylation; D000818:Animals; D001224:Aspartic Acid / Q000737:chemistry; D001665:Binding Sites; D003488:Cyanogen Bromide / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D004789:Enzyme Activation; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006801:Humans; D016548:Prosencephalon / Q000737:chemistry; D051381:Rats; D011976:Receptors, Muscarinic / Q000737:chemistry*; D011994:Recombinant Proteins
chemical_list: D004220:Disulfides; D011976:Receptors, Muscarinic; D011994:Recombinant Proteins; D001224:Aspartic Acid; C002561:acetylcholine mustard; D020558:GTP Phosphohydrolases; D000109:Acetylcholine; D003488:Cyanogen Bromide