Expression of a poriferan potassium channel: insights into the evolution of ion channels in metazoans

AbstractOur comparative studies seek to understand the structure and function of ion channels in cartilaginous fish that can detect very low voltage gradients in seawater. The principal channels of the electroreceptor include a calcium activated K channel, whose α subunit is Kcnma1, a voltage-dependent calcium channel, Cacna1d, and a relatively uncharacterized K channel which interacts with the calcium channel to produce fast (20 Hz) oscillations. Large conductance calcium-activated K channels (BK) are comprised of four α subunits, encoded by Kcnma1 and modulatory β subunits of the Kcnmb class. We recently cloned and published the skate Kcnma1 gene and most of Kcnmb4 derived from using purified mRNA of homogenized isolated electroreceptors. Bellono et al. have recently performed RNA sequencing (RNA-seq) on purified mRNA from skate electroreceptors and found several ion channels including Kcnma1. We searched the the Bellono et al RNA-seq repository for additional channels and subunits. Our most significant findings are the presence of two Shaker type voltage dependent potassium channel sequences which are grouped together as isoforms in the data repository. The larger of these is a skate ortholog of the voltage dependent fast potassium channel Kv1.1, which is expressed at appreciable levels and seems likely to explain the 20 Hz oscillations believed to occur in vivo. The second was more similar to Kv1.5 than to Kv1.1 but was somewhat atypical. We also found a beta subunit sequence (Kcnab2) which appears not to cause fast inactivation due to specific structural features. The new channels and subunits were verified by RT-PCR and the Kv1.1 sequence was confirmed by cloning. We also searched the RNA-seq repository for accessory subunits of the calcium activated potassium channel, Kcnma1, and found a computer generated assembly that contained a complete sequence of its beta subunit, Kcnmb2. Skate Kcnmb2 has a total of 279 amino acids, with 51 novel amino acids at the N-terminus which may play a specific physiological role. This sequence was confirmed by PCR and cloning. However, skate Kcnmb2 is expressed at low levels in the electroreceptor compared to Kcnma1 and skate Kcnmb1 (beta1) is absent. The evolutionary origin of the newly described channels and subunits was studied by aligning skate sequences with human sequences and those found in related fish: the whale shark (R. typus) an elasmobranch, and ghost shark (C.milii). There is also homology with the lamprey, which has electroreceptors. An evolutionary tree is presented. Further research should include focusing on the subcellular locations of these channels in the receptor cells, their gating behavior, and the effects of accessory subunits on gating.

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Differential roles of trithorax protein MLL-1 in regulating neuronal Ion channels

Journal of Neuroscience and Neurological Disorders ◽

10.29328/journal.jnnd.1001057 ◽

2021 ◽

Vol 5 (2) ◽

Author(s):

Dave Sonya ◽

Zhou An

Keyword(s):

Ion Channels ◽

Potassium Channel ◽

Polycomb Group ◽

Channel Activity ◽

Sodium Currents ◽

Trithorax Group ◽

Channel Protein ◽

Trxg Protein ◽

First Time ◽

Potassium Channel Activity

Repressive regulation of potassium channel genes by Polycomb group (PcG) proteins contributes to PcG protein-mediated neuroprotection against neuronal ischemic injury, as seen in an ischemic stroke. Here we asked the question whether Trithorax group (TrxG) proteins, the antagonistic partners of PcG proteins (i.e, epigenetic activators targeting the same genes) may also regulate potassium channels. Results of patch-clamp studies on cultured neuronal cells showed that inhibition of TrxG protein MLL-1 led to an increase in potassium channel activity, an unexpected effect for a presumed gene activator. In contrast, decreased sodium currents were observed with MLL-1 inhibition. Increased or decreased levels of potassium channel protein Kv2.1 or sodium channel protein Nav1.2, respectively, were seen with MLL-1 inhibition, as determined by immunocytochemistry. These results, for the first time, demonstrate an involvement of TrxG protein MLL-1 in regulating neuronal ion channels, potentially repressing potassium channel genes.

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Carbon nanoparticles enhance potassium uptake via upregulating potassium channel expression and imitating biological ion channels in BY-2 cells

Journal of Nanobiotechnology ◽

10.1186/s12951-020-0581-0 ◽

2020 ◽

Vol 18 (1) ◽

Author(s):

Lijuan Chen ◽

Jinchu Yang ◽

Xiang Li ◽

Taibo Liang ◽

Cong Nie ◽

...

Keyword(s):

Ion Channels ◽

Potassium Channel ◽

Carbon Nanoparticles ◽

Potassium Uptake ◽

Channel Expression

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Voltage-dependent gating and gating charge measurements in the Kv1.2 potassium channel

The Journal of General Physiology ◽

10.1085/jgp.201411300 ◽

2015 ◽

Vol 145 (4) ◽

pp. 345-358 ◽

Cited By ~ 26

Author(s):

Itzel G. Ishida ◽

Gisela E. Rangel-Yescas ◽

Julia Carrasco-Zanini ◽

León D. Islas

Keyword(s):

Ion Channels ◽

Potassium Channel ◽

Structural Data ◽

Activation Mechanism ◽

Voltage Sensitivity ◽

Structural Interpretation ◽

Kv Channel ◽

Gating Charge ◽

Voltage Dependent ◽

Electrophysiological Findings

Much has been learned about the voltage sensors of ion channels since the x-ray structure of the mammalian voltage-gated potassium channel Kv1.2 was published in 2005. High resolution structural data of a Kv channel enabled the structural interpretation of numerous electrophysiological findings collected in various ion channels, most notably Shaker, and permitted the development of meticulous computational simulations of the activation mechanism. The fundamental premise for the structural interpretation of functional measurements from Shaker is that this channel and Kv1.2 have the same characteristics, such that correlation of data from both channels would be a trivial task. We tested these assumptions by measuring Kv1.2 voltage-dependent gating and charge per channel. We found that the Kv1.2 gating charge is near 10 elementary charges (eo), ∼25% less than the well-established 13–14 eo in Shaker. Next, we neutralized positive residues in the Kv1.2 S4 transmembrane segment to investigate the cause of the reduction of the gating charge and found that, whereas replacing R1 with glutamine decreased voltage sensitivity to ∼50% of the wild-type channel value, mutation of the subsequent arginines had a much smaller effect. These data are in marked contrast to the effects of charge neutralization in Shaker, where removal of the first four basic residues reduces the gating charge by roughly the same amount. In light of these differences, we propose that the voltage-sensing domains (VSDs) of Kv1.2 and Shaker might undergo the same physical movement, but the septum that separates the aqueous crevices in the VSD of Kv1.2 might be thicker than Shaker’s, accounting for the smaller Kv1.2 gating charge.

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