Gating of retinal rod cation channel by different nucleotides: Comparative study of unitary currents

Ildefonse, M; Crouzy, Serge; Bennett, Nelly

doi:10.1007/bf00233741

Cited by 45 publications

(36 citation statements)

References 23 publications

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“…2 A, Table 1), indicating that mutations apparently did not affect cyclic nucleotide-binding or channel opening. We also determined the fractional activation of these channels by a saturating concentration of cAMP, a partial agonist that opens the channels poorly compared with cGMP (33,34). CNGA1 homomers had a characteristic low fractional activation by cAMP compared with cGMP, whereas CNGA1͞CNGB1 heteromers had a 10-fold higher fractional activation (Fig.…”

Section: Resultsmentioning

confidence: 99%

Mechanism of calcium/calmodulin inhibition of rod cyclic nucleotide-gated channels

Trudeau

Zagotta

2002

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

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Rod cyclic nucleotide-gated (CNG) channels are heterotetramers comprised of both CNGA1 and CNGB1 subunits. Calcium͞calmod-ulin (Ca 2؉ ͞CaM) binds to a site in the N-terminal region of CNGB1 subunits and inhibits the opening conformational change in CNGA1͞CNGB1 channels. Here, we show that polypeptides derived from an N-terminal region of CNGB1 form a specific interaction with polypeptides derived from a C-terminal region of CNGA1 that is distal to the cyclic nucleotide-binding domain. Deletion of the Ca 2؉ ͞CaM-binding site from the N-terminal region of CNGB1 eliminated both Ca 2؉ ͞CaM modulation of the channel and the intersubunit interaction. Furthermore, the interaction was disrupted by the presence of Ca 2؉ ͞CaM. These results suggest that Ca 2؉ ͞CaM-dependent inhibition of rod channels is caused by the direct binding of Ca 2؉ ͞CaM to a site in the N-terminal region in CNGB1, which disrupts the interaction between this region and a distal C-terminal region of CNGA1. The mechanism underlying Ca 2؉ ͞CaM modulation of rod channels is distinct from that in olfactory (CNGA2) CNG channels. C yclic nucleotide-gated (CNG) channels were first characterized in retinal rods, where they conduct a cation current in response to changes in intracellular levels of cGMP and mediate the electrical response to light (1). CNG channels also are found in olfactory neurons, where they respond to changes in internal cAMP and underlie the electrical response to odorants (2). Evidence exists for a cyclic nucleotide-dependent conductance in taste receptors (3,4). CNG channels are present in a variety of other tissues, including heart, aorta, and kidney (for a review see ref. 5).CNG channels were first cloned from retina (6) and olfactory neurons (7). Four channel subunits are arranged to form a tetramer with a central pore (8,9). Subunits have six proposed membrane-spanning domains, a pore-loop domain, and intracellular N-and C-terminal regions, a topology similar to that of the voltage-activated potassium channels (10). However, CNG channels are only weakly sensitive to membrane voltage. Instead, they contain a large C-terminal cyclic nucleotide-binding domain (CNBD) that exhibits sequence similarity with other cyclic nucleotide-binding proteins (11,12). CNG channels are activated by the direct binding of cyclic nucleotides to the CNBD (13).At present, there are six types of mammalian CNG channel genes. The genes are grouped according to sequence similarity into two subtypes, CNGA and CNGB (14). CNGA1, CNGA2, and CNGA3 subunits form functional homomeric channels when expressed alone, whereas CNGB1, CNGB3, and CNGA4 subunits do not appear to form functional homomeric channels when expressed alone. Instead, CNGB1, CNGB3, and CNGA4 subunits form heteromeric channels when coexpressed with CNGA1, CNGA2, or CNGA3 subunits (15).Native retinal rod channels comprise CNGA1 (formerly CNG1; Rod ␣) and CNGB1 (formerly CNG4; Rod ␤) subunits. CNGA1͞CNGB1 heterotetramers contain two CNGA1 subunits and two CNGB1 subunits (16,17). Compared with CNGA1 ...

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Section: Resultsmentioning

confidence: 99%

Mechanism of calcium/calmodulin inhibition of rod cyclic nucleotide-gated channels

Trudeau

Zagotta

2002

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

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“…Activation of the rod, but not the olfactory, CNG channel can be potentiated by transition metal divalent cations (19)(20)(21). This potentiation is seen as an increase in the apparent affinity for cGMP by -10-fold.…”

Section: Introductionmentioning

confidence: 93%

“…When coexpressed with the a subunits, these 13 subunits (or subunit 2) appear to confer properties of the native channels previously absent from the expressed channels (16-18). However, even these expressed heteromultimeric channels do not match the native channels in all aspects of their behavior, suggesting that other subunits or modulating factors may influence channel function.Activation of the rod, but not the olfactory, CNG channel can be potentiated by transition metal divalent cations (19)(20)(21). This potentiation is seen as an increase in the apparent affinity for cGMP by -10-fold.…”

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confidence: 93%

Subunit interactions in coordination of Ni2+ in cyclic nucleotide-gated channels.

Gordon

Zagotta

1995

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

105

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Cyclic nucleotide-gated (CNG) channels present a unique model for studying the molecular mechanisms of channel gating. We have studied the mechanism of potentiation of expressed rod CNG channels by Ni2+ as a first step toward understanding the channel gating process. Here we report that coordination of Ni2+ between histidine residues (H420) on adjacent channel subunits occurs when the channels are open. Mutation of H420 to lysine comptetely eliminated the potentiation by Ni2+ but did not markedly alter the apparent cGMP affinity of the channel, indicating that the introduction of positive charge at the Ni2+-binding site was not sufficient to produce potentiation. Deletion or mutation of most of the other histidines present in the channel did not diminish potentiation by Ni2+. We studied the role of subunit interactions in Ni2+ potentiation by generating heteromultimeric channels using tandem dimers of the rod CNG channel sequence. Injection of single heterodimers in which one subunit contained H420 and the other did not (wt/H420Q or H420Q/wt) resulted in channels that were not potentiated by Ni2+. However, coinjection of both heterodimers into Xenopus oocytes resulted in channels that exhibited potentiation. The H420 residues probably occurred predominantly in nonadjacent subunits when each heterodimer was injected individually, but, when the two heterodimers were coinjected, the H420 residues could occur in adjacent subunits as well. These results suggest that the mechanism of Ni2+ potentiation involves intersubunit coordination of Ni2+ by H420. Based on the preferential binding of Ni2+ to open channels, we suggest that alignment of H420 residues of neighboring subunits into the Ni2+-coordinating position may be associated with channel opening.Cyclic nucleotide-gated (CNG) channels transduce sensory information into electrical signals in rod and cone photoreceptors, avian pinealocyte photoreceptors, and olfactory receptors (1-3). These channels are also expressed in other tissues, such as kidney (4), aorta (5), and sperm (6), where their function is unknown. Although CNG channels are opened by the direct binding of cyclic nucleotides, they bear little functional or sequence similarity to other ligand-gated channels. Sequence similarity, especially in the pore region and transmembrane segments, places the CNG channels in the family of voltage-gated ion channels, along with voltage-gated K+, Na+, and Ca2+ channels (7). In addition, each CNG channel subunit has a region in its C-terminal domain that is similar in sequence to cAMP-and cGMP-dependent protein kinases (8, 9) and has been shown to bind a single cyclic nucleotide (10).CNG channels can be expressed as homomultimers of their primary subunit (a or subunit 1) (8,11 (16)(17)(18). When coexpressed with the a subunits, these 13 subunits (or subunit 2) appear to confer properties of the native channels previously absent from the expressed channels (16-18). However, even these expressed heteromultimeric channels do not match the native channels in all as...

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“…Maximal channel open probability (P max ) was determined from the ratio of currents at saturating cGMP (1 mM) in the absence and the presence of 1 M Ni 2ϩ . Ni 2ϩ was shown to potentiate currents induced by cGMP (Ildefonse et al, 1992;Gordon and Zagotta, 1995;Pagès et al, 2000), and the ratio described above was shown to be almost indistinguishable from the P max values obtained from singlechannel measurements (Sunderman and Zagotta, 1999). KCl or NaCl with Ͻ0.01 ppm Ni 2ϩ was used and HEPES concentration was 5 mM.…”

Section: Methodsmentioning

confidence: 82%

The Glutamic Acid-Rich Protein Is a Gating Inhibitor of Cyclic Nucleotide-Gated Channels

Michalakis¹,

Zong²,

Becirovic³

et al. 2011

J. Neurosci.

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The cyclic nucleotide-gated (CNG) cation channel of rod photoreceptors is a heterotetramer consisting of homologous CNGA1 and CNGB1a subunits. While CNGA1 is indispensable for channel activation, the specific role of CNGB1a in this process has remained elusive. Here, we show that the N-terminal glutamic acid-rich protein (GARP) domain of CNGB1a and soluble GARP2, which corresponds to the proximal portion of the GARP domain, act as autoinhibitory domains that decrease the opening probability of the CNG channel. In the presence of mutations that structurally impair the cyclic nucleotide-binding domain (CNBD) of CNGB1a, the GARP domain completely abolishes channel activity. In agreement with an inhibitory function of GARP, the activity of mutant CNG channels could be fully restored by deletion of the GARP domain. We identified two sequences within the GARP domain that confer most of the inhibitory effect and demonstrate that the profound inhibition imposed by the GARP domain is caused by direct and autonomous protein-protein interaction with the CNG channel complex. In wild-type rod CNG channels, this inhibitory effect can be relieved by binding of cGMP to the CNBD of CNGB1a. In conclusion, we propose that the N terminus of CNGB1a and soluble GARPs act as molecular gate keepers that control the activation of heteromeric rod CNG channels. Our results suggest that the GARP domain has evolved in rod photoreceptors to reduce current noise resulting from openings of CNG channels in the absence of cGMP.

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Gating of retinal rod cation channel by different nucleotides: Comparative study of unitary currents

Cited by 45 publications

References 23 publications

Mechanism of calcium/calmodulin inhibition of rod cyclic nucleotide-gated channels

Mechanism of calcium/calmodulin inhibition of rod cyclic nucleotide-gated channels

Subunit interactions in coordination of Ni2+ in cyclic nucleotide-gated channels.

The Glutamic Acid-Rich Protein Is a Gating Inhibitor of Cyclic Nucleotide-Gated Channels

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