Einblick - Structural Biology - # Conformational Changes in Kv1.2 Potassium Channels

Cryo-EM Structures of Kv1.2 Potassium Channels in Conducting and Non-Conducting States

Q: How do the structural differences between Kv1.2 and Shaker channels contribute to their distinct functional properties, such as gating charge movement and inactivation kinetics?

The structural differences between Kv1.2 and Shaker channels primarily lie in the voltage-sensing domains (VSDs) and the selectivity filter regions. While Kv1.2 and Shaker channels share a high degree of structural similarity, subtle variations in key residues within the VSDs can impact their functional properties. For example, the gating charge movement in Shaker channels is larger compared to Kv1.2, indicating differences in the physical displacement of the S4 helix. This difference in charge movement can be attributed to variations in the interactions between the voltage-sensing Arg and coordinating Glu and Asp residues in the VSDs. Additionally, mutations in the pore domain, such as W366F in Kv1.2, can lead to distinct inactivation kinetics. The W366F mutation destabilizes the selectivity filter, resulting in a dilation of the outer pore and disruption of ion-binding sites, leading to accelerated inactivation. In contrast, the corresponding mutation in Shaker channels (W434F) almost completely abolishes ion current, highlighting the impact of structural differences on functional properties.

Q: What are the potential implications of the Kv1.2 selectivity filter maintaining an intact structure in sodium-only solution, in contrast to the collapse observed in other channels?

The observation of the Kv1.2 selectivity filter maintaining an intact structure in a sodium-only solution, without collapsing like in other channels, has significant implications for ion selectivity and channel function. The intact structure of the selectivity filter in Kv1.2 suggests that the channel can conduct sodium ions efficiently, indicating a degree of flexibility in ion selectivity. This flexibility may allow Kv1.2 to function as a sodium channel under specific conditions, expanding its functional repertoire beyond potassium selectivity. The ability of Kv1.2 to maintain an intact selectivity filter in the absence of potassium ions highlights its adaptability to different ionic environments, potentially playing a role in diverse physiological processes where sodium conductance is required.

Q: Could the variable conformations of the C-type inactivated Kv1.2 W366F mutant in sodium solution suggest the existence of multiple inactivated states, and how might this relate to the channel's functional dynamics?

The variable conformations observed in the C-type inactivated Kv1.2 W366F mutant in sodium solution could indeed suggest the existence of multiple inactivated states with distinct structural configurations. These multiple inactivated states may represent different energy minima that the channel can adopt, each corresponding to a specific conformation of the selectivity filter and pore region. The presence of multiple inactivated states could reflect the channel's dynamic behavior during the inactivation process, where it transitions between different conformations based on environmental factors like ion concentrations. This structural heterogeneity in inactivated states may contribute to the channel's functional dynamics by influencing the kinetics of inactivation, the stability of the inactivated state, and the channel's ability to transition between conducting and non-conducting states in response to physiological cues.

Kernkonzepte

The cryo-EM structures of the mammalian voltage-gated potassium channel Kv1.2 reveal distinct ion-occupancy patterns in the selectivity filter under different functional states, including open, C-type inactivated, toxin-blocked, and sodium-bound conditions.

Zusammenfassung

The study presents near-atomic-resolution cryo-EM structures of the Kv1.2 potassium channel in various functional states. The key findings are:

The open, conducting state of Kv1.2 is very similar to the previously reported structures of the related Shaker channel and the Kv1.2-2.1 chimeric channel.
The C-type inactivated state of Kv1.2, obtained using the W366F mutation, shows a dramatic dilation of the selectivity filter, disrupting two of the four ion-binding sites. This is consistent with the inactivated structures of Shaker and Kv1.2-2.1 channels.
The toxin α-Dendrotoxin is observed to bind to the negatively-charged outer mouth of the Kv1.2 channel, with its lysine residue penetrating into the selectivity filter and partially disrupting the outermost ion-binding site.
Surprisingly, the structure of Kv1.2 in sodium-only solution does not show collapse or destabilization of the selectivity filter, but instead maintains an intact selectivity filter with ion density in each binding site.
Attempts to image the C-type inactivated Kv1.2 W366F channel in sodium solution resulted in a highly variable protein conformation, with only a low-resolution structure obtained.

These findings provide new insights into the stability of the Kv1.2 selectivity filter and the mechanisms of toxin block and C-type inactivation in this intensively studied voltage-gated potassium channel.

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Statistiken

The selectivity filter of the open Kv1.2 channel has four ion-binding sites, with potassium ion densities observed in each site.
The selectivity filter of the C-type inactivated Kv1.2 W366F mutant shows a dilation that disrupts two of the four ion-binding sites.
In the Kv1.2-Dendrotoxin complex, the selectivity filter has ion densities in only the lower two binding sites, with the lysine residue of the toxin penetrating into the upper site.
The Kv1.2 channel in sodium-only solution maintains an intact selectivity filter with ion densities in each of the four binding sites.

Zitate

"The cryo-EM structure of our rat Kv1.2 construct (Kv1.2s) in DDM detergent micelles agrees with the crystal structure of Long et al. (2005) and is very similar to the structure of Drosophila Shaker in lipid nanodiscs (Tan et al., 2022)."
"The expanded outer pore is very similar to the large extracellular vestibules observed in NaK and HCN1 channels."
"A striking feature of the inactivated state structure reported by Tan et al. (Reddi et al., 2022; Tan et al., 2022) is the high occupancy by potassium ions of the two remaining binding sites IS3 and IS4."

Wichtige Erkenntnisse aus

Cryo-EM structures of Kv1.2 potassium channels, conducting and non-conducting

by Wu,Y., Yan,Y... um www.biorxiv.org 06-03-2023

https://www.biorxiv.org/content/10.1101/2023.06.02.543446v2

Tiefere Fragen

How do the structural differences between Kv1.2 and Shaker channels contribute to their distinct functional properties, such as gating charge movement and inactivation kinetics?

The structural differences between Kv1.2 and Shaker channels primarily lie in the voltage-sensing domains (VSDs) and the selectivity filter regions. While Kv1.2 and Shaker channels share a high degree of structural similarity, subtle variations in key residues within the VSDs can impact their functional properties. For example, the gating charge movement in Shaker channels is larger compared to Kv1.2, indicating differences in the physical displacement of the S4 helix. This difference in charge movement can be attributed to variations in the interactions between the voltage-sensing Arg and coordinating Glu and Asp residues in the VSDs. Additionally, mutations in the pore domain, such as W366F in Kv1.2, can lead to distinct inactivation kinetics. The W366F mutation destabilizes the selectivity filter, resulting in a dilation of the outer pore and disruption of ion-binding sites, leading to accelerated inactivation. In contrast, the corresponding mutation in Shaker channels (W434F) almost completely abolishes ion current, highlighting the impact of structural differences on functional properties.

What are the potential implications of the Kv1.2 selectivity filter maintaining an intact structure in sodium-only solution, in contrast to the collapse observed in other channels?

The observation of the Kv1.2 selectivity filter maintaining an intact structure in a sodium-only solution, without collapsing like in other channels, has significant implications for ion selectivity and channel function. The intact structure of the selectivity filter in Kv1.2 suggests that the channel can conduct sodium ions efficiently, indicating a degree of flexibility in ion selectivity. This flexibility may allow Kv1.2 to function as a sodium channel under specific conditions, expanding its functional repertoire beyond potassium selectivity. The ability of Kv1.2 to maintain an intact selectivity filter in the absence of potassium ions highlights its adaptability to different ionic environments, potentially playing a role in diverse physiological processes where sodium conductance is required.

Could the variable conformations of the C-type inactivated Kv1.2 W366F mutant in sodium solution suggest the existence of multiple inactivated states, and how might this relate to the channel's functional dynamics?

The variable conformations observed in the C-type inactivated Kv1.2 W366F mutant in sodium solution could indeed suggest the existence of multiple inactivated states with distinct structural configurations. These multiple inactivated states may represent different energy minima that the channel can adopt, each corresponding to a specific conformation of the selectivity filter and pore region. The presence of multiple inactivated states could reflect the channel's dynamic behavior during the inactivation process, where it transitions between different conformations based on environmental factors like ion concentrations. This structural heterogeneity in inactivated states may contribute to the channel's functional dynamics by influencing the kinetics of inactivation, the stability of the inactivated state, and the channel's ability to transition between conducting and non-conducting states in response to physiological cues.