Biochemical characterization of a novel channel-activating site on nicotinic acetylcholine receptors.
We have studied the interaction of the reversible acetylcholine esterase inhibitor (-)physostigmine and several structurally related compounds with the nicotinic acetylcholine receptor (nAChR) from Torpedo marmorata electric tissue by means of ligand-induced ion flux into nAChR-rich membrane vesicles, direct binding studies and photoaffinity labeling. (-)Physostigmine acts as a channel-activating ligand at low concentrations and as a direct channel blocker at elevated concentrations. Channel activation is not inhibited by desensitizing concentrations of ACh or ACh-competitive ligands (including alpha-bungarotoxin and D-tubocurarine) but is inhibited by antibody FK1 and several other compounds. From photoaffinity labeling using tritiated physostigmine and mapping of the epitope for the Phy-competitive antibody FK1, the binding site for physostigmine is located within the alpha-subunit of the Torpedo nAChR and is distinct from the acetylcholine binding site. Our data suggest a second pathway of nAChR channel activation that may function physiologically as an allosteric control of receptor activity.
Schrattenholz
A
A
Laboratory of Molecular Neurobiology, Johannes-Gutenberg University Medical School, Mainz, Germany.
Coban
T
T
Schröder
B
B
Okonjo
K O
KO
Kuhlmann
J
J
Pereira
E F
EF
Albuquerque
E X
EX
Maelicke
A
A
D000595:Amino Acid Sequence; D000818:Animals; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects*; D008969:Molecular Sequence Data; D010830:Physostigmine / Q000378:metabolism / Q000494:pharmacology*; D011978:Receptors, Nicotinic / Q000187:drug effects* / Q000378:metabolism; D014101:Torpedo
D007473:Ion Channels; D011978:Receptors, Nicotinic; D010830:Physostigmine