Calcium-Calmodulin Modulation of the Olfactory Cyclic Nucleotide-Gated Cation Channel

Liu, Mingyao; Chen, Tsung‐Yu; Ahamed, Basheer; Li, Jess; Yau, King Wai

doi:10.1126/science.266.5189.1348

Cited by 290 publications

(247 citation statements)

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“…This is also in accordance with earlier studies of native channels from rat 17 , catfish 18 and frog OSNs 19 , although these studies were less clear on the molecular identification of the factor. Heterologous studies of homomeric CNGA2 channels, however, provide a prevailing yet contradictory view of how Ca 2+ -CaM-dependent modulation of native CNG channels occurs; calmodulin binds to the CNGA2 subunit only when it is complexed with Ca 2+ and it does not preassociate with the homomeric channel [4][5][6][7][8] . We reconciled these contradictory results by examining whether calmodulin preassociates with the native heteromeric configuration of CNG channels to facilitate rapid Ca 2+ -dependent modulation of cAMP sensitivity.…”

Section: Native Channels Preassociate With a Ca 2+ -Responsive Factormentioning

confidence: 99%

“…In the prevailing model for olfactory adaptation, however, no association of apocalmodulin at basal Ca 2+ concentrations has been described [4][5][6][7][8] . On the contrary, the calmodulin binding site identified in the N terminus of CNGA2 ( ref.…”

Section: Heteromeric Channels Bind Calmodulin In 0 Ca 2+mentioning

confidence: 99%

Section: Heteromeric Channels Bind Calmodulin In 0 Ca 2+mentioning

confidence: 99%

“…On the contrary, the calmodulin binding site identified in the N terminus of CNGA2 ( ref. 5 ) is a classic basic amphiphilic α-helix (Baa) motif 21 , with high affinity for Ca 2+ -CaM and no affinity for apocalmodulin [5][6][7] .To test whether, in the context of the native heteromeric configuration of the channel, the Baa motif of CNGA2 participates either in the binding of apocalmodulin or in subsequent channel modulation by Ca 2+ -CaM, we repeated the preassociation experiment with heteromeric channels containing a mutant CNGA2 subunit, CNGA2(F68A V75A) (CNGA2 mut ). This mutation abolishes both the binding of Ca 2+ -CaM to CNGA2 in vitro and the modulation by Ca 2+ -CaM of homomeric CNGA2 channels 7 .…”

mentioning

confidence: 99%

“…Rapid adaptation in OSNs is Ca 2+ dependent and is considered to be primarily an effect of modulation of cAMP sensitivity in CNG channels 2,3 . The currently accepted hypothesis for the mechanism of channel modulation is drawn from extensive studies of heterologously expressed homomeric CNGA2 channels, which show that calmodulin, when complexed with Ca 2+ (Ca 2+ -CaM), binds to an autoexcitatory domain of CNGA2, resulting in a reduced steady-state cAMP sensitivity [4][5][6][7][8] (for review, see ref. 9 ).…”

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Calmodulin permanently associates with rat olfactory CNG channels under native conditions

et al. 2004

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An important mechanism by which vertebrate olfactory sensory neurons rapidly adapt to odorants is feedback modulation of the Ca 2+ permeable cyclic nucleotide-gated (CNG) transduction channels. Extensive heterologous studies of homomeric CNGA2 channels have led to a molecular model of channel modulation based on the binding of calcium-calmodulin to a site on the cytoplasmic amino terminus of CNGA2. Native rat olfactory CNG channels, however, are heteromeric complexes of three homologous but distinct subunits. Notably, in heteromeric channels, we found no role for CNGA2 in feedback modulation. Instead, an IQ-type calmodulin-binding site on CNGB1b and a similar but previously unidentified site on CNGA4 are necessary and sufficient. These sites seem to confer binding of Ca 2+ -free calmodulin (apocalmodulin), which is then poised to trigger inhibition of native channels in the presence of Ca 2+ .Vertebrate olfactory sensory neurons (OSNs) convert chemical stimulation by odorant into an electrical signal. In OSNs, odorant binding to G-protein-coupled receptors stimulates an increase in intracellular 3′,5′-cyclic AMP (cAMP) concentration. This, in turn, leads to the opening of Ca 2+ -permeable CNG ion channels and the triggering of action potentials. The olfactory signal transduction pathway can be exquisitely sensitive. It can also rapidly and repeatedly adjust its sensitivity (or adapt) to stimulation (for review, see ref. 1 ). Rapid adaptation in OSNs is Ca 2+ dependent and is considered to be primarily an effect of modulation of cAMP sensitivity in CNG channels 2,3 . The currently accepted hypothesis for the mechanism of channel modulation is drawn from extensive studies of heterologously expressed homomeric CNGA2 channels, which show that calmodulin, when complexed with Ca 2+ (Ca 2+ -CaM), binds to an autoexcitatory domain of CNGA2, resulting in a reduced steady-state cAMP sensitivity 4-8 (for review, see ref. 9 ). We have since found, however, that this hypothesis is unsatisfactory, both mechanistically and kinetically, with respect to native channels and adaptation of OSNs 10 . For example, the binding of Ca 2+ -CaM to homomeric CNGA2 channels is strongly biased toward closed rather than open channels 10 . This is conspicuous because modulation of closed channels would be of little use during odorant stimulation of an OSN. Furthermore, homomeric CNGA2 channel modulation by Ca 2+ -CaM occurs too slowly (by two orders of magnitude) to account for adaptation in OSNs 10 . Taken together, these findings 14 . Here we focus on the native heteromeric configuration of the CNG channels of rat OSNs, addressing the possible combined contributions of CNGA2, CNGA4 and CNGB1b to the molecular mechanism underlying Ca 2+ -dependent adaptation. RESULTSNative channels preassociate with a Ca 2+ -responsive factorWe began by examining the interaction of calmodulin with native olfactory CNG channels of rat OSNs. We recorded CNG currents in excised, inside-out membrane patches from dendritic knobs of these cells, while ma...

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Section: Native Channels Preassociate With a Ca 2+ -Responsive Factormentioning

confidence: 99%

Section: Heteromeric Channels Bind Calmodulin In 0 Ca 2+mentioning

confidence: 99%

Section: Heteromeric Channels Bind Calmodulin In 0 Ca 2+mentioning

confidence: 99%

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confidence: 99%

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Calmodulin permanently associates with rat olfactory CNG channels under native conditions

et al. 2004

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1995

Arch Dermatol

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Cloning and immunocytochemical localization of a cyclic nucleotide-gated channel ?-subunit to all cone photoreceptors in the mouse retina

et al. 2000

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Cyclic nucleotide-gated channels (CNGC) are ligand-gated ion channels that open and close in response to changes in the intracellular concentration of the second messengers, 3′,5′-cyclic adenosine monophosphate and 3′,5′-cyclic guanosine monophosphate. Most notably, they transduce the chemical signal produced by the absorption of light in photoreceptors into a membrane potential change, which is then transmitted to the ascending visual pathway. CNGCs have also been implicated in the signal transduction of other neurons downstream of the photoreceptors, in particular the ONbipolar cells, as well as in other areas of the central nervous system. We therefore undertook a search for additional cyclic nucleotide-gated channels expressed in the retina. Following a degenerate reverse transcription polymerase chain reaction approach to amplify low-copy number messages, a cDNA encoding a new splice variant of CNGC α-subunit was isolated from mouse retina and classified as mCNG3. An antiserum raised against the carboxy-terminal sequence identified the retinal cell type expressing mCNG3 as cone photoreceptors. Preembedding immunoelectron microscopy demonstrated its membrane localization in the outer segments, consistent with its role in phototransduction. Double-labeling experiments with cone-specific markers indicated that all cone photoreceptors in the murid retina use the same or a highly conserved cyclic nucleotide-gated channel. Therefore, defects in this channel would be predicted to severely impair photopic vision. Indexing termsrat; calcium/calmodulin; phototransduction Cyclic nucleotide-gated channels (CNGC) are nonselective cation channels, constructed out of αand β-subunits in a likely tetrameric configuration, with intracellular ligand-binding domain(s). When expressed in heterologous systems, the α-subunits can form functional ion channels. With the coexpression of the αand β-subunits, the channels acquire additional characteristics that reflect those seen in situ (Kaupp, 1995;Molday, 1996;Wei et al., 1998), for example, the ability to be modulated by calcium (Chen et al., 1993;Körschen et al., 1995). These channels are highly regulated (Zimmerman, 1995) and may be the downstream effectors of nitric oxide-signaling mechanisms (Ahmad et al., 1994;Savchenko et al., 1997).

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Calcium-Calmodulin Modulation of the Olfactory Cyclic Nucleotide-Gated Cation Channel

Cited by 290 publications

References 48 publications

Calmodulin permanently associates with rat olfactory CNG channels under native conditions

Calmodulin permanently associates with rat olfactory CNG channels under native conditions

Scratch and Sniff

Cloning and immunocytochemical localization of a cyclic nucleotide-gated channel ?-subunit to all cone photoreceptors in the mouse retina

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