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Crystallographic insights into sodium-channel modulation by the ?4 subunit.

ABSTRACT: Voltage-gated sodium (Nav) channels are embedded in a multicomponent membrane signaling complex that plays a crucial role in cellular excitability. Although the mechanism remains unclear, ?-subunits modify Nav channel function and cause debilitating disorders when mutated. While investigating whether ?-subunits also influence ligand interactions, we found that ?4 dramatically alters toxin binding to Nav1.2. To explore these observations further, we solved the crystal structure of the extracellular ?4 domain and identified (58)Cys as an exposed residue that, when mutated, eliminates the influence of ?4 on toxin pharmacology. Moreover, our results suggest the presence of a docking site that is maintained by a cysteine bridge buried within the hydrophobic core of ?4. Disrupting this bridge by introducing a ?1 mutation implicated in epilepsy repositions the (58)Cys-containing loop and disrupts ?4 modulation of Nav1.2. Overall, the principles emerging from this work (i) help explain tissue-dependent variations in Nav channel pharmacology; (ii) enable the mechanistic interpretation of ?-subunit-related disorders; and (iii) provide insights in designing molecules capable of correcting aberrant ?-subunit behavior.

SUBMITTER: Gilchrist J

PROVIDER: S-EPMC3870679 | biostudies-literature | 2013 Dec

REPOSITORIES: biostudies-literature

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Crystallographic insights into sodium-channel modulation by the β4 subunit.

Gilchrist John J Das Samir S Van Petegem Filip F Bosmans Frank F Bosmans Frank F

Proceedings of the National Academy of Sciences of the United States of America 20131202 51

Voltage-gated sodium (Nav) channels are embedded in a multicomponent membrane signaling complex that plays a crucial role in cellular excitability. Although the mechanism remains unclear, β-subunits modify Nav channel function and cause debilitating disorders when mutated. While investigating whether β-subunits also influence ligand interactions, we found that β4 dramatically alters toxin binding to Nav1.2. To explore these observations further, we solved the crystal structure of the extracellul ...[more]

PMID: 24297919

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Project description:Sodium channels are chief proteins involved in electrical signaling in the nervous system, enabling critical functions like heartbeat and brain activity. New high-resolution X-ray structures for bacterial sodium channels have created an opportunity to see how these proteins operate at the molecular level. An important challenge to overcome is establishing relationships between the structures and functions of mammalian and bacterial channels. Bacterial sodium channels are known to exhibit the main structural features of their mammalian counterparts, as well as several key functional characteristics, including selective ion conduction, voltage-dependent gating, pore-based inactivation and modulation by local anesthetic, antiarrhythmic and antiepileptic drugs. Simulations have begun to shed light on each of these features in the past few years. Despite deviations in selectivity signatures for bacterial and mammalian channels, simulations have uncovered the nature of the multiion conduction mechanism associated with Na(+) binding to a high-field strength site established by charged glutamate side chains. Simulations demonstrated a surprising level of flexibility of the protein, showing that these side chains are active participants in the permeation process. They have also uncovered changes in protein structure, leading to asymmetrical collapses of the activation gate that have been proposed to correspond to inactivated structures. These observations offer the potential to examine the mechanisms of state-dependent drug activity, focusing on pore-blocking and pore-based slow inactivation in bacterial channels, without the complexities of inactivation on multiple timescales seen in eukaryotic channels. Simulations have provided molecular views of the interactions of drugs, consistent with sites predicted in mammalian channels, as well as a wealth of other sites as potential new drug targets. In this chapter, we survey the new insights into sodium channel function that have emerged from studies of simpler bacterial channels, which provide an excellent learning platform, and promising avenues for mechanistic discovery and pharmacological development.

Dataset Information

Crystallographic insights into sodium-channel modulation by the ?4 subunit.

Publications

Crystallographic insights into sodium-channel modulation by the β4 subunit.

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