Acetylcholine binding sites

Stauffer, D.A., and Karlin, A. (1994) Electrostatic potential of the acetylcholine binding sites in the nicotinic receptor probed by reaction of binding-site cysteines with charged methanethiosulfonates. Biochemistry 33, 6840-6849. 

Nakanishi studied philanthotoxin (polyamine-amide) interaction with nicotinic acetylcholine ion-channel [58]. Philanthotoxin-133 (PhTX-133) is a noncompetitive channel-blocker found in venom of the wasp Philanthus. Nicotinic acetylcholine ion-channel is composed of five transmembrane subunits (a, o, P, y, and S), which forms a 270-kDa glycoprotein. The major acetylcholine binding sites are in the a,ex subunits. A 43-kDa cytoplasmic protein is associated non-covalently with the receptor, but interaction with the receptor is not essential for the channel opening (Fig. 6). 

Middleton RE, Cohen JB. 1991. Mapping of the acetylcholine binding site of the nicotinic acetylcholine receptor [ H] nicotine as an agonist photoaffinity label. Biochemistry 30 6987-6997. 

The site of inhibition is in case of hexamethonium in the sodium channel, whereas trimethaphan blocks the acetylcholine binding site of the receptor. 

Whitehouse PJ, Price DL, Clark AW, et al Alzheimer disease evidence for selective loss of cholinergic neurons in the nucleus basahs. Ann Neurol 10 122-126, 1981 Whitehouse PJ, Price DL, Struble RG, et al Alzheimer s disease and senile dementia—loss of neurons in the basal forebrain. Science 215 1237-1239, 1982 Whitehouse PJ, Hedreen JC, White CL, et al Basal forebrain neurons in dementia of Parkinson s disease. Ann Neurol 13 243-248, 1983 Whitehouse P, Martino A, Antuono P, et al Nicotinic acetylcholine binding sites in Alzheimer s disease. Brain Res 371 146-151, 1986 Whitehouse PJ, Martino AM, Marcus KA, et al Reductions in acetylcholine and nicotine binding in several degenerative diseases. Arch Neurol 45 722-724, 1988 Whitton PS, Sama GS, O Connell MT The effect of the novel antidepressant tianeptine on the concentration of 5-hydroxytryptamine in rat hippocampal diasylates in vivo. Neuropharmacology 39 1-4, 1991 Whitworth P, Kendall DA Lithium selectively inhibits muscarinic receptor-stimulated inositol tetrakisphosphate accumulation in mouse cerebral cortex slices. J Neurochem 51 258-265, 1988... 

A high-affinity competing ligand for the acetylcholine binding site in the nAChR. 

The nicotinic acetylcholine receptor has five subunits single copies of subunits /3, y, and 8, and two identical a subunits each with an acetylcholine-binding site. All five subunits are related in sequence and tertiary structure, each having four transmembrane helical... 

Figure 9.3. Electron microscopy and electron crystallography of the nicotinic acetylcholine receptor (NAR). a NAR channels in liposome membranes. On the left, they are mostly randomly oriented (but some form a more regular pattern). On the right, a regularly packed two-dimensional crystal has formed. Such samples can be used to obtain a three-dimensional structure at low resolution by electron crystallography, b Electron crystallographic structure, represented as density contour maps. Left Top view. Middle, right Side view. The bilayer and the portions of the receptor protruding from it into both directions are visible. The arrow in the right frame points to the acetylcholine binding site.

Both pancuronium and d-tubocurarine act by binding to the NAR in a way competitive with acetylcholine. In both cases, the presence of both positive charges is important for activity. Yet, it is questionable whether both cationic groups bind simultaneously to the two acetylcholine binding sites found (at the two a chains) of the NAR, since the distance between those should substantially exceed the one between the two charges in the antagonist molecules. 

Local anaesthetics and barbiturates appear to prevent the changes in ion permeability which would normally result from the interaction of acetylcholine with its receptor. They do not, however, bind to the acetylcholine binding site. It is believed that they bind instead to the part of the receptor which is on the inside of the cell membrane, perhaps binding to the ion channel itself and blocking it. 

Czajkowski, C., Karlin, A., 1995. Structure of the nicotinic receptor acetylcholine-binding site. Identification of acidic residues in the 8 subunit within 0.9 nm of the a subunit-binding site disulfide. J. Biol. Chem. 270, 3160-3164. 

Fig. 12.7. Nicotinic cholinergic receptor. (A) Longitudinal view (y subunit removed) showing the internal ion channel. Acetylcholine binding sites on the a subunits are indicated by the arrows. These are located at the ay and a5 interfaces. (B) Each of the five transmembrane subunits (a, a, 3, 5, and y) are composed of four hydrophobic membrane spanning segments (M1-M4). (C) Top view of the nicotinic receptor showing the subunits surrounding the ion channel.

Nordberg A, Winblad B. Reduced number of [H Jnicotine and [H ] acetylcholine binding sites in the frontal cortex of Alzheimer brains. Neurosci Lett 1986 72 115-119. 

Whitehouse PJ, Martino AM, Antuono PG, et al. Nicotinic acetylcholine binding sites in Alzheimer s disease. Brain Res 1986 371 146-151. 

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