Ca2+ channel selectivity at a single locus for high-affinity Ca2+ interactions

Ellinor, Patrick T.; Yang, Jian; Sather, William A.; Zhang, Jifang; Tsien, Richard W.

doi:10.1016/0896-6273(95)90100-0

Cited by 268 publications

(326 citation statements)

References 32 publications

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“…It is likely that Ca 2ϩ channels also use backbone carbonyl groups to bind Ca 2ϩ whereas the four acidic residues of the EEEE locus, shown by mutagenesis to be the sole element determining Ca 2ϩ selectivity (24)(25)(26), confer Ca 2ϩ specificity through similar mechanisms as seen here in NaK. This model is more readily reconciled with the plethora of evidence suggesting that Ca 2ϩ channels have multi-ion pores when compared with concurrent views of a single, flexible, and rapidly rearranging Ca 2ϩ binding site formed by the EEEE locus (27).…”

Section: Discussionmentioning

confidence: 99%

Structural insight into Ca ²⁺ specificity in tetrameric cation channels

Alam

Shi

Jiang

2007

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

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Apparent blockage of monovalent cation currents by the permeating blocker Ca 2؉ is a physiologically essential phenomenon relevant to cyclic nucleotide-gated (CNG) channels. The recently determined crystal structure of a bacterial homolog of CNG channel pores, the NaK channel, revealed a Ca 2؉ binding site at the extracellular entrance to the selectivity filter. This site is not formed by the side-chain carboxylate groups from the conserved acidic residue, Asp-66 in NaK, conventionally thought to directly chelate Ca 2؉ in CNG channels, but rather by the backbone carbonyl groups of residue Gly-67. Here we present a detailed structural analysis of the NaK channel with a focus on Ca 2؉ permeability and blockage. Our results confirm that the Asp-66 residue, although not involved in direct chelation of Ca 2؉ , plays an essential role in external Ca 2؉ binding. Furthermore, we give evidence for the presence of a second Ca 2؉ binding site within the NaK selectivity filter where monovalent cations also bind, providing a structural basis for Ca 2؉ permeation through the NaK pore. Compared with other Ca 2؉ -binding proteins, both sites in NaK present a novel mode of Ca 2؉ chelation, using only backbone carbonyl oxygen atoms from residues in the selectivity filter. The external site is under indirect control by an acidic residue (Asp-66), making it Ca 2؉ -specific. These findings give us a glimpse of the possible underlying mechanisms allowing Ca 2؉ to act both as a permeating ion and blocker of CNG channels and raise the possibility of a similar chemistry governing Ca 2؉ chelation in Ca 2؉ channels.calcium blockage ͉ cyclic nucleotide-gated channel pore ͉ NaK channel ͉ nonselective cation channel

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Section: Discussionmentioning

confidence: 99%

Structural insight into Ca ²⁺ specificity in tetrameric cation channels

Alam

Shi

Jiang

2007

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

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“…Voltage-operated Ca 2ϩ channels compromise four glutamate residues in the putative pore region, which are likely to be responsible for the high Ca 2ϩ selectivity (24,25). Electrostatic interaction between these glutamate residues and Ca 2ϩ are a critical determinant of high affinity Ca 2ϩ binding and permeation properties, suggesting that these negative residues could behave as surrogate water molecules to facilitate the passage of dehydrated Ca 2ϩ through the hydrophobic plasma membrane (26).…”

Section: Discussionmentioning

confidence: 99%

Voltage-dependent Changes of TRPV6-mediated Ca2+ Currents

Bödding

2005

Journal of Biological Chemistry

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“…In brief, Rat α 1D (14) was engineered (E716A) to enhance permeation of Li + over Ca 2+ (17,18), and expressed in HEK293 cells as described (23). This mutant was used in all experiments.…”

Section: Methodsmentioning

confidence: 99%

Ca ²⁺ channel nanodomains boost local Ca ²⁺ amplitude

Tadross

Tsien

Yue

2013

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

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Local Ca 2+ signals through voltage-gated Ca 2+ channels (Ca V s) drive synaptic transmission, neural plasticity, and cardiac contraction. Despite the importance of these events, the fundamental relationship between flux through a single Ca V channel and the Ca 2+ signaling concentration within nanometers of its pore has resisted empirical determination, owing to limitations in the spatial resolution and specificity of fluorescence-based Ca 2+ measurements. Here, we exploited Ca 2+ -dependent inactivation of Ca V channels as a nanometer-range Ca 2+ indicator specific to active channels. We observed an unexpected and dramatic boost in nanodomain Ca 2+ amplitude, ten-fold higher than predicted on theoretical grounds. Our results uncover a striking feature of Ca V nanodomains, as diffusion-restricted environments that amplify small Ca 2+ fluxes into enormous local Ca 2+ concentrations. This Ca 2+ tuning by the physical composition of the nanodomain may represent an energy-efficient means of local amplification that maximizes information signaling capacity, while minimizing global Ca 2+ load.L ocal Ca 2+ signals increase the information capacity of signaling within a cell, by enabling short-range signals to operate independently of Ca 2+ events elsewhere throughout the cell (1, 2). These local Ca 2+ signals are the conduit that drives diverse activity-dependent events, such as synaptic transmission (3), neural plasticity (4-6), and cardiac excitation-contraction coupling (7). However, with regard to the Ca 2+ amplitude within nanometers of individual Ca 2+ channels, our knowledge is based predominantly on diffusion theory, which predicts ∼100 μM Ca 2+ signals per picoampere flux at a distance of ∼10 nm from the pore (8-11). Although often quoted, this theory has been difficult to verify experimentally because diffusible Ca 2+ indicators report space-averaged [Ca 2+ ], and thus lack the spatial resolution needed for selective nanodomain reporting. Two recent efforts to overcome this limitation used voltage-gated Ca 2+ channel (Ca V )-tethered fluorescent Ca 2+ indicators to isolate nanodomain signals (12, 13), but were met with unexpected difficulties: Ca V -tethered indicators were unresponsive in the presence of high concentrations of intracellular 1,2-bis(oaminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), a Ca 2+ buffer that preserves Ca 2+ elevations within tens of nanometers of active channels but eliminates it elsewhere (8-10). A lack of response under these conditions would arise if the majority of tethered channels were silent, raising the concern that fluorescence changes observed under milder Ca 2+ buffering (12, 13) may represent the response of indicators tethered to silent channels, which nonetheless eavesdrop on Ca 2+ from active channels nearby. To overcome this fundamental limitation, we used a reverse strategy, whereby Ca 2+ /calmodulin-dependent inactivation (CDI) of channels themselves serves as a nanometer-range indicator of [Ca 2+ ]; a sensitive ionic readout that is unaffected by the pres...

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Ca2+ channel selectivity at a single locus for high-affinity Ca2+ interactions

Cited by 268 publications

References 32 publications

Structural insight into Ca ²⁺ specificity in tetrameric cation channels

Structural insight into Ca ²⁺ specificity in tetrameric cation channels

Voltage-dependent Changes of TRPV6-mediated Ca2+ Currents

Ca ²⁺ channel nanodomains boost local Ca ²⁺ amplitude

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Ca2+ channel selectivity at a single locus for high-affinity Ca2+ interactions

Cited by 268 publications

References 32 publications

Structural insight into Ca 2+ specificity in tetrameric cation channels

Structural insight into Ca 2+ specificity in tetrameric cation channels

Voltage-dependent Changes of TRPV6-mediated Ca2+ Currents

Ca 2+ channel nanodomains boost local Ca 2+ amplitude

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Resources

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Structural insight into Ca ²⁺ specificity in tetrameric cation channels

Structural insight into Ca ²⁺ specificity in tetrameric cation channels

Ca ²⁺ channel nanodomains boost local Ca ²⁺ amplitude