NDLI: [3H]Chlorpromazine Photolabeling of the Torpedo Nicotinic Acetylcholine Receptor Identifies Two State-Dependent Binding Sites in the Ion Channel†

Content Provider	PubMed Central
Author	Chiara, David C. Hamouda, Ayman K. Ziebell, Michael R. Mejia, Luis A. Garcia, Galo Cohen, Jonathan B.
Abstract	Chlorpromazine (CPZ), a potent nicotinic acetylcholine receptor (nAChR) noncompetitive antagonist, binds with higher affinity in the ion channel in the desensitized state than in the closed channel state and with low affinity to additional sites in nAChR-rich membranes. For nAChR equilibrated with agonist, we confirm previous reports that [3H]CPZ occupies a site near the cytoplasmic end of the M2 ion channel domain, photolabeling positions M2-2, M2-6 and/or M2-9 in each subunit. We find that [3H]CPZ also binds at the extracellular end of the channel, photolabeling amino acids at positions M2-16 (α,γ), M2-17 (α,β,δ), and M2-20 (α,β,δ). The photolabeling at the cytoplasmic end of the channel is fully inhibitable by phencyclidine or proadifen, whereas neither drug inhibits [3H]CPZ photolabeling at the extracellular end, establishing that positively charged drugs can bind simultaneously at the cytoplasmic and extracellular ends of the ion channel. [3H]CPZ photolabeling is not detected in the transmembrane domain outside the ion channel, but it photolabels αMet-386 & αSer-393 in the cytoplasmic αMA helix. In the nAChR equilibrated with α-bungarotoxin to stabilize the nAChR in a closed state, [3H]CPZ photolabels amino acids at M2-5 (α), M2-6 (α,β,δ) and M2-9 (β,δ), with no labeling at M2-2. These results provide novel information about the modes of drug binding within the nAChR ion channel and indicate that within the nAChR transmembrane domain, the binding of cationic aromatic amine antagonists can be restricted to the ion channel domain, in contrast to the uncharged, allosteric potentiators and inhibitors that also bind within the δ subunit helix bundle and at subunit interfaces.
Related Links	http://dx.doi.org/10.1021/bi901271w
Ending Page	10077
Page Count	12
Starting Page	10066
File Format	PDF
ISSN	00062960
e-ISSN	15204995
Journal	Biochemistry
Issue Number	42
Volume Number	48
Language	English
Publisher Date	2009-10-27
Access Restriction	Open
Subject Keyword	Biochemistry Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Biochemistry

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