The Permeation Pathway of Neurotransmitter-Gated Ion Channels

Lester, Henry A.

doi:10.1146/annurev.bb.21.060192.001411

Cited by 146 publications

(83 citation statements)

References 83 publications

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“…Similar positions with respect to Ser and Thr have been used in simulations on M2 from influenza A (22,35), the pore-lining segments of M2 from nicotinic acetylcholine receptor (nAChR) (36,37), and a synthetic ion channel peptide Ac-(LSLLLSL) 3 -CONH 2 (38). In the case of the nAChR the positions are experimentally confirmed (reviewed in refs [39][40][41]. The placement of the Ser and Thr in the NB transmembrane segment consequently places the phenylalanines on the outside of each bundle.…”

Section: Sequencementioning

confidence: 75%

Transmembrane Peptide NB of Influenza B: A Simulation, Structure, and Conductance Study

et al. 2000

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The putative transmembrane segment of the ion channel forming peptide NB from influenza B was synthesized by standard solid-phase peptide synthesis. Insertion into the planar lipid bilayer revealed ion channel activity with conductance levels of 20, 61, 107, and 142 pS in a 0.5 M KCl buffer solution. In addition, levels at -100 mV show conductances of 251 and 413 pS. A linear current-voltage relation reveals a voltage-independent channel formation. In methanol and in vesicles the peptide appears to adopt an R-helical-like structure. Computational models of R-helix bundles using N ) 4, 5, and 6 NB peptides per bundle revealed water-filled pores after 1 ns of MD simulation in a solvated lipid bilayer. Calculated conductance values [using HOLE (Smart et al. (1997) Biophys. J. 72, 1109-1126] of ca. 20, 60, and 90 pS, respectively, suggested that the multiple conductance levels seen experimentally must correspond to different degrees of oligomerization of the peptide to form channels.In the genome of influenza B, RNA segment 6 encodes two integral membrane proteins, NB and NA. NB is a protein of ca. 100 amino acids. It has ca. 18 extramembraneous residues on its N-terminal end, a 22-residue membrane spanning segment, and a ca. 60 residue long C-terminal end (1, 2). NB is expressed at the surface of infected cells (3)(4)(5). In the virion the N-terminal site is located at the external surface. Experiments with gold immunolabeled freezefractured virions indicate that the C-terminus is located at the inside of the virion (4). By analogy with the M2 protein of influenza A, it was suggested (reviewed in ref 6) that NB might be a channel-forming protein.Conductance measurements with purified NB expressed in Escherichia coli and reconstituted in lipid bilayers reveal a conductance of 45 pS. However, when NB is incorporated in liposomes and then added to planar lipid bilayers, the conductance ranged from ca. 10 pS at very low NB concentration in the liposomes to several hundred picosiemens for higher concentrations (7). At neutral pH the channels are more permeable for sodium ions than chloride ions (P Na /P Cl ≈ 9 at pH 6.5). In asymmetrical NaCl solutions at pH 2.5 the permeability is higher for chloride ions (P Cl / P Na ≈ 4). A recent study on NB expressed in the plasmalemma of MEL 1 cells showed that the channel peptides induce a Na + -dependent proton current and a pH-activated Cl -current (8).One way in which single integral membrane proteins can form ion channels is via oligomerization to form a bundle of transmembrane helices. For the analogous channel peptide in influenza A, M2, it is believed that a tetrameric R-helix bundle is the minimal form of the proton-permeable ion channel (9-11). For NB the number of subunits in the bundle is not known. Purification of NB on gels using nonreducing conditions revealed the formation of disulfide-linked dimers and higher oligomers (2). Molecular modeling studies on bundles of the transmembrane parts of the peptide have been performed in vacuo with four, five, and si...

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Section: Sequencementioning

confidence: 75%

Transmembrane Peptide NB of Influenza B: A Simulation, Structure, and Conductance Study

et al. 2000

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“…Selectivity of the Mouse Nicotinic Acetytcholine Receptor 393 pore (reviewed by Lester, 1992). In our view, the nAChR subunits have an a-helical secondary structure at this region, so that positions -1' and 2' are on the same side of an a-helix, approximately one turn apart.…”

Section: Positions -1' and 2' Are The Narrowest Part Of The Al3y~ Porementioning

confidence: 99%

“…We used the Woodhull (1973) model to determine the location of the amylammonium binding site in the electric field of the channel. This formulation has proven useful for many open-channel blockers (Lester, 1992); based on such analysis it is reasonable to assume that (a) the channel is nonconducting when amylammonium occupies its binding site, (b) block by amylammonium is in rapid equilibrium during the voltage ramp used to generate the I-V relation, and (c) amylammonium binding follows conventional first-order kinetics. Then…”

Section: And(v)mentioning

confidence: 99%

Mutations in M2 alter the selectivity of the mouse nicotinic acetylcholine receptor for organic and alkali metal cations.

Cohen

Labarca

Davidson

et al. 1992

The Journal of General Physiology

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116

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We measured the permeability ratios (Px/PNa) of 3 wild-type, 1 hybrid, 2 subunit-deficient, and 22 mutant nicotinic receptors expressed in Xen0pus oocytes for alkali metal and organic cations using shifts in the biionic reversal potential of the macroscopic current. Mutations at three positions (2', 6', 10') in M2 affected ion selectivity. Mutations at position 2' (t~Thr244, 13Gly255, ~/Thr253, 8Ser258) near the intracellular end of M2 changed the organic cation permeability ratios as much as twofold and reduced Pc~/PNa and PK/PNa by 16-18%. Mutations at positions 6' and 10' increased the glycine ethyl ester/Na + and glycine methyl ester/Na + permeability ratios. Two subunit alterations also affected selectivity: omission of the 8 subunit reduced PcJPsa by 16%, and substitution ofXenopus 8 for mouse 8 increased P~nidi~ium/PNa more than twofold and reduced Pcs/PN~ by 34% and PLi/PN~ by 20%. The wild-type mouse receptor displayed a surprising interaction with the primary ammonium cations; relative permeability peaked at a chain length equal to four carbons. Analysis of the organic permeability ratios for the wild-type mouse receptor shows that (a) the diameter of the narrowest part of the pore is 8.4 ,~; (b) the mouse receptor departs significantly from size selectivity for monovalent organic cations; and (c) lowering the temperature reduces Pguanidinium/ PNa by 38% and Pbutylanunonitun/PNa more than twofold. The results reinforce present views that positions -1' and 2' are the narrowest part of the pore and suggest that positions 6' and 10' align some permeant organic cations in the pore in an interaction similar to that with channel blocker, QX-222.

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“…Like the MscL mechanosensitive ion channel 16 , glycine 23 , acetylcholine 17 , GABA A and serotonin (5HT 3 ) receptors 24 , the CorA transporter is assembled as a pentamer. However, beyond this common pentameric organization, the CorA transporter is quite different.…”

mentioning

confidence: 99%

Crystal structure of the CorA Mg2+ transporter

Лунин

Dobrovetsky²,

Khutoreskaya³

et al. 2006

Nature

236

301

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The magnesium ion, Mg 2+ , is essential for myriad biochemical processes and remains the only major biological ion whose transport mechanisms remain unknown. The CorA family of magnesium transporters is the primary Mg 2+ uptake system of most prokaryotes 1-3 and a functional homologue of the eukaryotic mitochondrial magnesium transporter 4 . Here we determine crystal structures of the full-length Thermotoga maritima CorA in an apparent closed state and its isolated cytoplasmic domain at 3.9 Å and 1.85Å resolution, respectively. The transporter is a funnel-shaped homopentamer with two transmembrane helices per monomer. The channel is formed by an inner group of five helices and putatively gated by bulky hydrophobic residues. The large cytoplasmic domain forms a funnel whose wide mouth points into the cell and whose walls are formed by five long helices that are extensions of the transmembrane helices. The cytoplasmic neck of the pore is surrounded, on the outside of the funnel, by a ring of highly conserved positively charged residues. Two negatively charged helices in the cytoplasmic domain extend back towards the membrane on the outside of the funnel and abut the ring of positive charge. An apparent Mg 2+ ion was bound between monomers at a conserved site in the cytoplasmic domain, suggesting a mechanism to link gating of the pore to the intra-cellular concentration of Mg 2+ . The CorA magnesium transporter is a homopentamer with fivefold symmetry about a central pore and can be divided into three parts (Fig. 1). A carboxy-terminal transmembrane domain comprises two transmembrane helices from each monomer (Fig. 2). The middle portion resembles a funnel, narrow at the entrance ( 5 Å) and wide at the mouth ( 20Å), that is formed largely by a long -helix extension of the inner transmembrane helix. Finally, a large cytoplasmic domain lies exterior to the funnel.The cytoplasmic domain of CorA is a seven-stranded parallel/antiparallel -sheet ( 2 1 3 7 6 5 4 ) sandwiched between two sets of -helices ( 1, 2, 3) and ( 4, 5, 6) ( Fig. 1). The domain fold is unlike all other known structures of ion channels or transporters and constitutes a new protein fold (see Supplementary Information). This domain, solved in its soluble form at 1.85 Å resolution ( Supplementary Fig. S1), is linked to the transmembrane helices by the long 7 helix (residues 251-312), termed the stalk helix. The stalk helix kinks as it enters the membrane, extends through the membrane, forms the first transmembrane helix (TM1; residues 293-312) and harbours the 'YGMNF' signature sequence of CorA (residues 311-315) 5,6 ( Fig. 2 and Supplementary Fig. S2). The five TM1 helices (residues 293-312) form the pore. After a short extracellular seven-amino-acid loop, the TM2 helix (residues 326-345) returns back to the cytoplasm and ends in a highly conserved C-terminal KKKKWL motif (Fig. 3). In the current structure, neither the extracellular loop nor the final two amino acids could be resolved.The cytoplasmic domain shows the lowest sequence conservati...

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The Permeation Pathway of Neurotransmitter-Gated Ion Channels

Cited by 146 publications

References 83 publications

Transmembrane Peptide NB of Influenza B: A Simulation, Structure, and Conductance Study

Transmembrane Peptide NB of Influenza B: A Simulation, Structure, and Conductance Study

Mutations in M2 alter the selectivity of the mouse nicotinic acetylcholine receptor for organic and alkali metal cations.

Crystal structure of the CorA Mg2+ transporter

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