The positively charged C-terminal region of the inactivating Shaker B peptide binds to the potassium channel KcsA

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K+ channels are universally involved in electrical activity in muscles and nerves, and also in regulating salt and water transport in tissues implicated in metabolism. The prokaryotic KcsA K+ channel has become a structural archetype for the pore domain of voltage-dependent channels. The binding of the inactivating peptide from the eukaryotic Shaker B K+ channel (ShB peptide) to either asolectin-reconstituted or DDM-solubilised KcsA has been shown to occur mainly through the hydrophobic region of the peptide (namely, residues Val4, Tyr8, Leu7 and Leu10). In this work, we studied the binding of a deletion variant of the ShB peptide, where the first 11 residues, and then, the hydrophobic region, have been removed (Δ(1–11)ShB). The aim of this work is to elucidate whether binding to KcsA can also occur through the highly charged C-terminal region of ShB peptide. The STD-NMR experiments indicate that there is binding of Δ(1–11)ShB to either asolectin-reconstituted or DDM-solubilised KcsA. The protons showing the largest effects are those of the side-chain of His16, and probably, the backbone amide protons of both Lys18 and Lys19. These results indicate that the hydrophobic residues in ShB peptide are not necessary to ensure binding to the channel, and then, binding to KcsA is also driven by electrostatic interactions.

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