A single negative charge within the pore region of a cGMP-gated channel controls rectification, Ca2+ blockage, and ionic selectivity.

Eismann, Elisabeth; Müller, Frank; Heinemann, Stefan; Kaupp, U. Benjamin

doi:10.1073/pnas.91.3.1109

Cited by 183 publications

(137 citation statements)

References 55 publications

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“…The pattern of open-channel modification with Ag ϩ supports the suggestion that the structure of the selectivity filter from the bacterial nonselective cation channel is a reasonable model of the selectivity filter of CNG channels (31). Crystal structures determined in the presence of divalent ions show unambiguously that divalent ions bind at the external mouth of the selectivity filter (31), which has been functionally reported in CNG channels (35)(36)(37)(38). If intracellularly applied Ag ϩ is using the selectivity filter to access position T364C, we should expect that external divalent ions would, by electrostatic and/or steric reasons, interfere with the Ag ϩ reaction.…”

Section: Resultssupporting

confidence: 53%

Gating at the selectivity filter in cyclic nucleotide-gated channels

Contreras

Srikumar²,

Holmgren³

2008

Proc. Natl. Acad. Sci. U.S.A.

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By opening and closing the permeation pathway (gating) in response to cGMP binding, cyclic nucleotide-gated (CNG) channels serve key roles in the transduction of visual and olfactory signals. Compiling evidence suggests that the activation gate in CNG channels is not located at the intracellular end of pore, as it has been established for voltage-activated potassium (KV) channels. Here, we show that ion permeation in CNG channels is tightly regulated at the selectivity filter. By scanning the entire selectivity filter using small cysteine reagents, like cadmium and silver, we observed a state-dependent accessibility pattern consistent with gated access at the middle of the selectivity filter, likely at the corresponding position known to regulate structural changes in KcsA channels in response to low concentrations of permeant ions.cGMP ͉ ion channel ͉ signal transduction C yclic nucleotide-gated (CNG) channels sense variations in the intracellular concentration of cyclic nucleotides that occur in response to visual or olfactory stimuli, therefore playing essential roles in the transduction of visual and olfactory information (1, 2). In many ways, CNG channels are similar to voltage-activated potassium (K V ) channels. They coassemble as tetramers of homologous subunits (3-6), each containing six transmembrane segments (TM), a positively charged TM4 and a reentry P region between TM5 and TM6, suggesting that CNG channels belong to the same superfamily of voltage-activated cation channels (7). The main difference is that CNG channels are only weakly voltage-dependent. Instead, they open and close the pore in response to changes in the intracellular concentrations of cGMP or cAMP, a property conferred by the presence of a cyclic nucleotide binding domain at the C terminus of each subunit (8, 9).Our understanding of how CNG channels open and close their pore in response to cyclic nucleotide binding is much less refined than our understanding of how K V channels gate in response to voltage. A large body of evidence, using a variety of approaches, has established that K V channels open and close their permeation pathway at the intracellular end of the pore (10-17). Attempts to extend those ideas to CNG channels have encountered some resistance. For example, studies using intracellularly applied molecules that block the permeation pathway of CNG channels, such as divalent ions (18), tetracaine (19,20), or quaternary ammonium ions (21), have shown that blockade is not state-dependent, as if these molecules can access the pore in both open and closed channels, which is in stark contrast with the blockade properties observed in K V channels (10,11,14,(22)(23)(24). In addition, experiments examining the state dependence of cysteine modification by intracellular application of methanethiosulfonate (MTS) reagents have failed to show dramatic differences between open and closed states in the inner-vestibule region (21,25,26), results that are inconsistent with an intracellular gate in TM6, as shown in K V channels (12,15).Se...

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Section: Resultssupporting

confidence: 53%

Gating at the selectivity filter in cyclic nucleotide-gated channels

Contreras

Srikumar²,

Holmgren³

2008

Proc. Natl. Acad. Sci. U.S.A.

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“…The single-channel conductance of the rod CNG channel pore may be reduced 200-fold by selective binding of Ca 2+ to acidic residues in the pore region (34). This effect has been reported for high, nonphysiological levels [Ca 2+ ]i.…”

Section: The Role Of Ca 2+ In Light Adaptationmentioning

confidence: 92%

Calcium regulation in photoreceptors

2002

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In this review we describe some of the remarkable and intricate mechanisms through which the calcium ion (Ca 2+ ) contributes to detection, transduction and synaptic transfer of light stimuli in rod and cone photoreceptors. The function of Ca 2+ is highly compartmentalized. In the outer segment, Ca 2+ controls photoreceptor light adaptation by independently adjusting the gain of phototransduction at several stages in the transduction chain. In the inner segment and synaptic terminal, Ca 2+ regulates cells' metabolism, glutamate release, cytoskeletal dynamics, gene expression and cell death. We discuss the mechanisms of Ca 2+ entry, buffering, sequestration, release from internal stores and Ca 2+ extrusion from both outer and inner segments, showing that these two compartments have little in common with respect to Ca 2+ homeostasis. We also investigate the various roles played by Ca 2+ as an integrator of intracellular signaling pathways, and emphasize the central role played by Ca 2+ as a second messenger in neuromodulation of photoreceptor signaling by extracellular ligands such as dopamine, adenosine and somatostatin. Finally, we review the intimate link between dysfunction in photoreceptor Ca 2+ homeostasis and pathologies leading to retinal dysfunction and blindness. KeywordsRetina; Photoreceptor; Rod; Cone; Calcium; Plasma Membrane Calcium Atpase; Na-Ca Exchange; Calcium Store; Calcium Buffering; Calcium Channel; Calcium Extrusion; Ryanodine; Inner Segment; Dystrophy; Synaptic Transmission; Review INTRODUCTIONThe calcium ion (Ca 2+ ) is a major messenger for coordinating activity of eukaryote cells. Its extensive distribution and functioning as a control ion is common to a huge range of eukaryote cell types from animal, plant or fungal sources which diverged billions of years ago. The signaling potential of Ca 2+ is linked to the ability of cells to maintain a large concentration gradient between the cytosol (with basal Ca 2+ levels typically ~ 50 nM) and the extracellular media (with Ca 2+ ~ 1.5 mM). Because of this 10,000-fold difference in [Ca 2+ ]i between the cytosol and the extracellular space, Ca 2+ influx across the plasma membrane and Ca 2+ release from intracellular stores may produce large fluctuations of free cytosolic Ca 2+ (1). Another important feature of Ca 2+ homeostasis is that [Ca 2+ ]i elevations in the cell can be highly localized. We now know that the diffusion of Ca 2+ within the cytosol is much slower than that of other intracellular messengers (2,3). Ca 2+ is thus able to regulate a variety of different functions in different parts of the cell. Such selective action of Ca 2+ is facilitated by Ca 2+ -binding proteins which are often localized to specific sites mediating individual functions (4). To understand Ca 2+ signaling, it is therefore essential to map the spatial distribution of Ca 2+ effector proteins such as Ca 2+ channels, Ca 2+ pumps, cytoplasmic buffers and intracellular Anatomically, primary sensory neurons are notable for their compartmentalization into input ...

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“…Similar phenomena have been noted in track-etched nanopores in poly(ethylene terephthalate), 5,10 glass pipets with tapering small tips (20-100 nm), 11,12 and biological channels. 13,14 Uneven electrostatic field effects from inhomogeneous surface charge distribution or asymmetric geometry are believed to be responsible for current rectification. 9 Together, all of these observations led us to conclude that the variable cation selectivity we measured was due to variable surface charge.…”

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confidence: 99%

Atomic Layer Deposition to Fine-Tune the Surface Properties and Diameters of Fabricated Nanopores

et al. 2004

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Atomic layer deposition of alumina enhanced the molecule sensing characteristics of fabricated nanopores by fine-tuning their surface properties, reducing 1/f noise, neutralizing surface charge to favor capture of DNA and other negative polyelectrolytes, and controlling the diameter and aspect ratio of the pores with near single Ångstrom precision. The control over the chemical and physical nature of the pore surface provided by atomic layer deposition produced a higher yield of functional nanopore detectors.

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A single negative charge within the pore region of a cGMP-gated channel controls rectification, Ca2+ blockage, and ionic selectivity.

Cited by 183 publications

References 55 publications

Gating at the selectivity filter in cyclic nucleotide-gated channels

Gating at the selectivity filter in cyclic nucleotide-gated channels

Calcium regulation in photoreceptors

Atomic Layer Deposition to Fine-Tune the Surface Properties and Diameters of Fabricated Nanopores

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