Acetylcholine receptor mapping

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. 

Sullivan D, Cohen JB. 2000. Mapping the agonist binding site of the nicotinic acetylcholine receptor orientation requirements for activation by covalent agonist. J Biol Chem 275 12651-12660. 

Goldman D, Simmons D, Swanson LW, Patrick J, Heinemann S (1986) Mapping of brain areas expressing RNA homologous to two different acetylcholine receptor a-subunits. Proc Nad Acad Sci 83 4076 080... 

F. Liang, F.l. Carroll, M.J. Kuhar, Mapping nicotinic acetylcholine receptors with PET, Synapse 24 (1996) 403-407. 

Y.S. Ding, F. Liang, J.S. Fowler, M.J. Kuhar, F.l. Carroll, Synthesis of [ F]norchloro-fluoroepibatidine and its N-methyl derivative New PET ligands for mapping nicotinic acetylcholine receptors, J. Label. Compds Radiopharm. 39 (1997) 828-832. 

Fig. 16.13. Pore structure of the acetylcholine receptor, based on electron microscopy studies. a) Electron density map of the acetylcholine receptor of the postsynaptic membrane of the electric organ of the ray Torpedo californicus, based on electron microscopy studies. The receptor has a long funnel-like structure in the extracellular region, which narrows at the center of the pore. A smaller funnel structure is observed in the cytoplasmic region of the receptor. Another protein is situated on the cytoplasmic side. The long arrow indicates the direction of ion passage and the small arrow shows the postulated binding site for acetylcholine, b) Schematic representation of the acetylcholine receptor with the M2 hehx as the central block in the ion channel. According to Unwin, (1993).

Fig. 16.14. Configuration of the M2 helices of the acetylcholine receptor in the closed and open states. The schematic representation is based on a comparison of the electron density map of the acetylcholine receptor in closed and open states. Only three of the five M2 helices are shown, a) Closed state the M2 helices are bent at the middle. The leucine residues point into the interior of the pore and prevent passage of ions, b) Open state the M2 helices are turned outwards at a tangent and the bulky leucine residues are removed from the center of the pore. Reorientation of the M2 helices causes a reorientation of polar amino adds that coat the interior of the pore. The polar amino acids (Ser and Thr residues) are oriented closer to the center of the pore and create a hydrophilic coating of the pore inner wall, which facilitates ion passage. According to Unwin,...

Tzartos, S. J., Rand, D. E., Einarson, B. L., and Lindstrom, J. M. (1981) Mapping of surface structures of Electrophorus acetylcholine receptor using monoclonal antibodies. J Biol. Chem 256, 8635-8645. 

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.

With the exception of true 3D crystals, which must be sectioned to make them thin enough to study by transmission electron mi-croscopy,the resolutions obtained with biological specimens are generally dictated by the preservation of periodic order, and the symmetry and complexity of the object. Hence, studies of the helical acetylcholine receptor tubes (36), the icosahedral hepatitis B virus capsid (44), the SOS ribosome (45), and the centriole (26) have yielded 3D density maps at resolutions of 4.6, 7.4, 15, and 280 A, respectively. 

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