Crystallographic insights into sodium-channel modulation by the beta4 subunit.
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Gilchrist J, Das S, Van Petegem F, Bosmans F
Crystallographic insights into sodium-channel modulation by the beta4 subunit.
Proc Natl Acad Sci U S A. 2013 Dec 17;110(51):E5016-24. doi: 10.1073/pnas.1314557110. Epub 2013 Dec 2.
- PubMed ID
- 24297919 [ View in PubMed]
- 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, beta-subunits modify Nav channel function and cause debilitating disorders when mutated. While investigating whether beta-subunits also influence ligand interactions, we found that beta4 dramatically alters toxin binding to Nav1.2. To explore these observations further, we solved the crystal structure of the extracellular beta4 domain and identified (58)Cys as an exposed residue that, when mutated, eliminates the influence of beta4 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 beta4. Disrupting this bridge by introducing a beta1 mutation implicated in epilepsy repositions the (58)Cys-containing loop and disrupts beta4 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 beta-subunit-related disorders; and (iii) provide insights in designing molecules capable of correcting aberrant beta-subunit behavior.