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Regions of KCNQ K(+) channels controlling functional expression.

Choveau FS, Shapiro MS - Front Physiol (2012)

Bottom Line: Despite similar structures, KCNQ2 and KCNQ3 homomers yield small current amplitudes compared to other KCNQ homomers and KCNQ2/3 heteromers.The second mechanism suggests networks of interactions between the pore helix and the selectivity filter (SF), and between the pore helix and the S6 domain that govern KCNQ current amplitudes.Here, we summarize the role of these different regions in expression of functional KCNQ channels.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Health Science Center at San Antonio San Antonio, TX, USA.

ABSTRACT
KCNQ1-5 α-subunits assemble to form K(+) channels that play critical roles in the function of numerous tissues. The channels are tetramers of subunits containing six transmembrane domains. Each subunit consists of a pore region (S5-pore-S6) and a voltage-sensor domain (S1-S4). Despite similar structures, KCNQ2 and KCNQ3 homomers yield small current amplitudes compared to other KCNQ homomers and KCNQ2/3 heteromers. Two major mechanisms have been suggested as governing functional expression. The first involves control of channel trafficking to the plasma membrane by the distal part of the C-terminus, containing two coiled-coiled domains, required for channel trafficking and assembly. The proximal half of the C-terminus is the crucial region for channel modulation by signaling molecules such as calmodulin (CaM), which may mediate C- and N-terminal interactions. The N-terminus of KCNQ channels has also been postulated as critical for channel surface expression. The second mechanism suggests networks of interactions between the pore helix and the selectivity filter (SF), and between the pore helix and the S6 domain that govern KCNQ current amplitudes. Here, we summarize the role of these different regions in expression of functional KCNQ channels.

No MeSH data available.


Networks of interactions in the pore region controlling KCNQ3 gating. Shown is a schematic representation of the pore region of wild-type KCNQ3 (A). Shown are structural rearrangements resulting from creation of hydrogen bonds between the pore helix and the SF (B) or the disruption of the van der Waals interaction between the S6 domain and the pore helix (C) (adapted from Choveau et al., 2012b).
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Figure 1: Networks of interactions in the pore region controlling KCNQ3 gating. Shown is a schematic representation of the pore region of wild-type KCNQ3 (A). Shown are structural rearrangements resulting from creation of hydrogen bonds between the pore helix and the SF (B) or the disruption of the van der Waals interaction between the S6 domain and the pore helix (C) (adapted from Choveau et al., 2012b).

Mentions: Our lab suggests that pore instability is responsible for small KCNQ3 currents, compared to other KCNQ channels. Based on patch-clamp experiments and homology modeling, we identified two networks of interactions between the pore helix and the SF, and between the pore helix and the S6 domain, controlling KCNQ3 gating (Figure 1A). Formation of hydrogen bonds between a hydrophilic residue at position 315 (A315T, S) and the I312 in the pore helix led to ~15-fold increase of current amplitude, compared to wild-type KCNQ3, modeled as stabilizing the SF in a conductive conformation (Zaika et al., 2008) (Figure 1B). In contrast, a hydrophilic residue at position 312 (I312E, I312K, and I312R) was suggested to form destabilizing hydrogen bonds with the top of the SF, affecting the conductive pathway of KCNQ3 and that of KCNQ3 (A315T) (Figure 1B) (Choveau et al., 2012a). Because the residues involved in this network of interactions are highly conserved in KCNQ channels, such interactions could affect the stability of the SF in other KCNQ channels. Indeed, a hydrophilic residue at position 273 (I312 in KCNQ3) in KCNQ2 resulted in a decrease of current amplitude, comparable to that observed in KCNQ3 suggesting similar mechanisms may apply to other KCNQ channels. Interactions between the pore helix and the top of the SF may also promote the channel conductive pathway (Uehara et al., 2008). Indeed, the W309R mutation in the pore helix of KCNQ3 led to a decrease of current compared to wild-type channels that would arise from the destabilization of pore helix-SF interactions. A homology model, based on the crystal structure of Kv1.2, proposed that an arginine (R309), in contrast to a tryptophan residue in wild-type channels, is not close enough to Y319 to make a hydrogen bond. Finally, a second network of interactions between the pore helix and the S6 domain has been postulated as governing KCNQ current amplitudes (Seebohm et al., 2005; Panaghie et al., 2008; Choveau et al., 2012b). In KCNQ3, a phenylalanine (F344) in the S6 domain has been suggested to be close enough to form a van der Waals interaction with the pore helix at A315, stabilizing the conductive pathway (Figure 1C). Disruption of this interaction, by mutating F344 to A, C, or W, resulted in a ~5-fold-decrease of current amplitude compared to wild-type KCNQ3 (Choveau et al., 2012b). As mentioned above, the T315-I312 bond is thought to promote the channel conductive pathway. This stabilizing effect is modeled as abolished by the disruption of the F344-A315 interaction, arguing for a dominant role of this interaction over the T315-I312 bond in KCNQ3 gating (Figure 1C). Interestingly, mutations of the equivalent phenylalanine (F340) in KCNQ1 affect its function as well (Seebohm et al., 2005; Panaghie et al., 2008). The predicted structure of the pore region of KCNQ1, based on the crystal structure of KcsA, suggests this phenylalanine may interact with the pore helix (V310), but with the homologous residue next to A315 in KCNQ3 (Seebohm et al., 2005). This indicates pore helix-S6 interactions might play a role in gating for all KCNQ channels.


Regions of KCNQ K(+) channels controlling functional expression.

Choveau FS, Shapiro MS - Front Physiol (2012)

Networks of interactions in the pore region controlling KCNQ3 gating. Shown is a schematic representation of the pore region of wild-type KCNQ3 (A). Shown are structural rearrangements resulting from creation of hydrogen bonds between the pore helix and the SF (B) or the disruption of the van der Waals interaction between the S6 domain and the pore helix (C) (adapted from Choveau et al., 2012b).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 1: Networks of interactions in the pore region controlling KCNQ3 gating. Shown is a schematic representation of the pore region of wild-type KCNQ3 (A). Shown are structural rearrangements resulting from creation of hydrogen bonds between the pore helix and the SF (B) or the disruption of the van der Waals interaction between the S6 domain and the pore helix (C) (adapted from Choveau et al., 2012b).
Mentions: Our lab suggests that pore instability is responsible for small KCNQ3 currents, compared to other KCNQ channels. Based on patch-clamp experiments and homology modeling, we identified two networks of interactions between the pore helix and the SF, and between the pore helix and the S6 domain, controlling KCNQ3 gating (Figure 1A). Formation of hydrogen bonds between a hydrophilic residue at position 315 (A315T, S) and the I312 in the pore helix led to ~15-fold increase of current amplitude, compared to wild-type KCNQ3, modeled as stabilizing the SF in a conductive conformation (Zaika et al., 2008) (Figure 1B). In contrast, a hydrophilic residue at position 312 (I312E, I312K, and I312R) was suggested to form destabilizing hydrogen bonds with the top of the SF, affecting the conductive pathway of KCNQ3 and that of KCNQ3 (A315T) (Figure 1B) (Choveau et al., 2012a). Because the residues involved in this network of interactions are highly conserved in KCNQ channels, such interactions could affect the stability of the SF in other KCNQ channels. Indeed, a hydrophilic residue at position 273 (I312 in KCNQ3) in KCNQ2 resulted in a decrease of current amplitude, comparable to that observed in KCNQ3 suggesting similar mechanisms may apply to other KCNQ channels. Interactions between the pore helix and the top of the SF may also promote the channel conductive pathway (Uehara et al., 2008). Indeed, the W309R mutation in the pore helix of KCNQ3 led to a decrease of current compared to wild-type channels that would arise from the destabilization of pore helix-SF interactions. A homology model, based on the crystal structure of Kv1.2, proposed that an arginine (R309), in contrast to a tryptophan residue in wild-type channels, is not close enough to Y319 to make a hydrogen bond. Finally, a second network of interactions between the pore helix and the S6 domain has been postulated as governing KCNQ current amplitudes (Seebohm et al., 2005; Panaghie et al., 2008; Choveau et al., 2012b). In KCNQ3, a phenylalanine (F344) in the S6 domain has been suggested to be close enough to form a van der Waals interaction with the pore helix at A315, stabilizing the conductive pathway (Figure 1C). Disruption of this interaction, by mutating F344 to A, C, or W, resulted in a ~5-fold-decrease of current amplitude compared to wild-type KCNQ3 (Choveau et al., 2012b). As mentioned above, the T315-I312 bond is thought to promote the channel conductive pathway. This stabilizing effect is modeled as abolished by the disruption of the F344-A315 interaction, arguing for a dominant role of this interaction over the T315-I312 bond in KCNQ3 gating (Figure 1C). Interestingly, mutations of the equivalent phenylalanine (F340) in KCNQ1 affect its function as well (Seebohm et al., 2005; Panaghie et al., 2008). The predicted structure of the pore region of KCNQ1, based on the crystal structure of KcsA, suggests this phenylalanine may interact with the pore helix (V310), but with the homologous residue next to A315 in KCNQ3 (Seebohm et al., 2005). This indicates pore helix-S6 interactions might play a role in gating for all KCNQ channels.

Bottom Line: Despite similar structures, KCNQ2 and KCNQ3 homomers yield small current amplitudes compared to other KCNQ homomers and KCNQ2/3 heteromers.The second mechanism suggests networks of interactions between the pore helix and the selectivity filter (SF), and between the pore helix and the S6 domain that govern KCNQ current amplitudes.Here, we summarize the role of these different regions in expression of functional KCNQ channels.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Health Science Center at San Antonio San Antonio, TX, USA.

ABSTRACT
KCNQ1-5 α-subunits assemble to form K(+) channels that play critical roles in the function of numerous tissues. The channels are tetramers of subunits containing six transmembrane domains. Each subunit consists of a pore region (S5-pore-S6) and a voltage-sensor domain (S1-S4). Despite similar structures, KCNQ2 and KCNQ3 homomers yield small current amplitudes compared to other KCNQ homomers and KCNQ2/3 heteromers. Two major mechanisms have been suggested as governing functional expression. The first involves control of channel trafficking to the plasma membrane by the distal part of the C-terminus, containing two coiled-coiled domains, required for channel trafficking and assembly. The proximal half of the C-terminus is the crucial region for channel modulation by signaling molecules such as calmodulin (CaM), which may mediate C- and N-terminal interactions. The N-terminus of KCNQ channels has also been postulated as critical for channel surface expression. The second mechanism suggests networks of interactions between the pore helix and the selectivity filter (SF), and between the pore helix and the S6 domain that govern KCNQ current amplitudes. Here, we summarize the role of these different regions in expression of functional KCNQ channels.

No MeSH data available.