Dataset Information

GlialCAM, a CLC-2 Cl(-) channel subunit, activates the slow gate of CLC chloride channels.

ABSTRACT: GlialCAM, a glial cell adhesion molecule mutated in megalencephalic leukoencephalopathy with subcortical cysts, targets the CLC-2 Cl(-) channel to cell contacts in glia and activates CLC-2 currents in vitro and in vivo. We found that GlialCAM clusters all CLC channels at cell contacts in vitro and thus studied GlialCAM interaction with CLC channels to investigate the mechanism of functional activation. GlialCAM slowed deactivation kinetics of CLC-Ka/barttin channels and increased CLC-0 currents opening the common gate and slowing its deactivation. No functional effect was seen for common gate deficient CLC-0 mutants. Similarly, GlialCAM targets the common gate deficient CLC-2 mutant E211V/H816A to cell contacts, without altering its function. Thus, GlialCAM is able to interact with all CLC channels tested, targeting them to cell junctions and activating them by stabilizing the open configuration of the common gate. These results are important to better understand the physiological role of GlialCAM/CLC-2 interaction.

SUBMITTER: Jeworutzki E

PROVIDER: S-EPMC4156679 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

GlialCAM, a CLC-2 Cl(-) channel subunit, activates the slow gate of CLC chloride channels.

Jeworutzki Elena E Lagostena Laura L Elorza-Vidal Xabier X López-Hernández Tania T Estévez Raúl R Pusch Michael M

Biophysical journal 20140901 5

GlialCAM, a glial cell adhesion molecule mutated in megalencephalic leukoencephalopathy with subcortical cysts, targets the CLC-2 Cl(-) channel to cell contacts in glia and activates CLC-2 currents in vitro and in vivo. We found that GlialCAM clusters all CLC channels at cell contacts in vitro and thus studied GlialCAM interaction with CLC channels to investigate the mechanism of functional activation. GlialCAM slowed deactivation kinetics of CLC-Ka/barttin channels and increased CLC-0 currents ...[more]

PMID: 25185546

Similar Datasets

Project description:CLC-0, a prototype Cl- channel in the CLC family, employs two gating mechanisms that control its ion-permeation pore: fast gating and slow gating. The negatively-charged sidechain of a pore glutamate residue, E166, is known to be the fast gate, and the swinging of this sidechain opens or closes the pore of CLC-0 on the millisecond time scale. The other gating mechanism, slow gating, operates with much slower kinetics in the range of seconds to tens or even hundreds of seconds, and it is thought to involve still-unknown conformational rearrangements. Here, we find that low intracellular pH (pHi) facilitates the closure of the CLC-0's slow gate, thus generating current inhibition. The rate of low pHi-induced current inhibition increases with intracellular H+ concentration ([H+]i)-the time constants of current inhibition by low pHi = 4.5, 5.5 and 6 are roughly 0.1, 1 and 10 sec, respectively, at room temperature. In comparison, the time constant of the slow gate closure at pHi = 7.4 at room temperature is hundreds of seconds. The inhibition by low pHi is significantly less prominent in mutants favoring the slow-gate open state (such as C212S and Y512A), further supporting the fact that intracellular H+ enhances the slow-gate closure in CLC-0. A fast inhibition by low pHi causes an apparent inverted voltage-dependent activation in the wild-type CLC-0, a behavior similar to those in some channel mutants such as V490W in which only membrane hyperpolarization can open the channel. Interestingly, when V490W mutation is constructed in the background of C212S or Y512A mutation, the inverted voltage-dependent activation disappears. We propose that the slow kinetics of CLC-0's slow-gate closure may be due to low [H+]i rather than due to the proposed large conformational change of the channel protein. Our results also suggest that the inverted voltage-dependent opening observed in some mutant channels may result from fast closure of the slow gate by the mutations.

Project description:The two human CLC Cl(-) channels, ClC-Ka and ClC-Kb, are almost exclusively expressed in kidney and inner ear epithelia. Mutations in the genes coding for ClC-Kb and barttin, an essential CLC-K channel beta subunit, lead to Bartter syndrome. We performed a biophysical analysis of the modulatory effect of extracellular Ca(2+) and H(+) on ClC-Ka and ClC-Kb in Xenopus oocytes. Currents increased with increasing [Ca(2+)](ext) without full saturation up to 50 mM. However, in the absence of Ca(2+), ClC-Ka currents were still 20% of currents in 10 mM [Ca(2+)](ext), demonstrating that Ca(2+) is not strictly essential for opening. Vice versa, ClC-Ka and ClC-Kb were blocked by increasing [H(+)](ext) with a practically complete block at pH 6. Ca(2+) and H(+) act as gating modifiers without changing the single-channel conductance. Dose-response analysis suggested that two protons are necessary to induce block with an apparent pK of approximately 7.1. A simple four-state allosteric model described the modulation by Ca(2+) assuming a 13-fold higher Ca(2+) affinity of the open state compared with the closed state. The quantitative analysis suggested separate binding sites for Ca(2+) and H(+). A mutagenic screen of a large number of extracellularly accessible amino acids identified a pair of acidic residues (E261 and D278 on the loop connecting helices I and J), which are close to each other but positioned on different subunits of the channel, as a likely candidate for forming an intersubunit Ca(2+)-binding site. Single mutants E261Q and D278N greatly diminished and the double mutant E261Q/D278N completely abolished modulation by Ca(2+). Several mutations of a histidine residue (H497) that is homologous to a histidine that is responsible for H(+) block in ClC-2 did not yield functional channels. However, the triple mutant E261Q/D278N/H497M completely eliminated H(+) -induced current block. We have thus identified a protein region that is involved in binding these physiologically important ligands and that is likely undergoing conformational changes underlying the complex gating of CLC-K channels.

Dataset Information

GlialCAM, a CLC-2 Cl(-) channel subunit, activates the slow gate of CLC chloride channels.

Publications

GlialCAM, a CLC-2 Cl(-) channel subunit, activates the slow gate of CLC chloride channels.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets