Structural insights into the potency of SK channel positive modulators

Figures

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  Figure 1. SK channel positive modulators. (a) The chemical structures of NS309, 1-EBIO, SKS-11 and SKS-14. (b) Raw current traces of dose-dependent channel potentiation by SKS-11 in the presence of 0.1 μM Ca2+. (c) Raw current traces of dose-dependent channel potentiation by SKS-14 in the presence of 0.1 μM Ca2+. (d) Dose-dependent potentiation of the SK2 current by NS309, SKS-11, SKS-14 and 1-EBIO, respectively. All data are presented in mean ± s.e.m.

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  Figure 2. Shared binding site of the SK channel positive modulators. (a) Electron density map (grey, |F o|-|F c|) showing the presence of additional electron density at the interface between CaM (cyan) and the CaMBD (salmon). The map is contoured at 3.7 σ and is overlaid with the current refined coordinates for SKS-11. (b) Electron density map (grey) showing the presence of additional electron density. The map is contoured at 3.7 σ and is overlaid with the current refined coordinates for SKS-14. (c) NS309, SKS-11, SKS-14 and 1-EBIO all bind to the interface between the CaM (cyan) N-lobe and the CaMBD (salmon). (d) Overlaid conformations of compounds obtained from their respective protein complex crystal structures. The carbon atoms of the compounds are shown in pale green (NS309), grey (SKS-11), magenta (SKS-14) and yellow (1-EBIO).

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  Figure 3. Eint between the compounds and their binding pocket. (a) Stacked column plot showing the total Eint that is composed of VDW Eint (grey) and electrostatic Eint (white). (b) The correlation between the total Eint and the potency of NS309, SKS-11, SKS-14 and 1-EBIO (r = 0.99). (c) The correlation between the electrostatic Eint and the potency of NS309, SKS-11, SKS-14 and 1-EBIO (r = 0.91). (d) The lack of correlation between the VDW Eint and the potency of NS309, SKS-11, SKS-14 and 1-EBIO (r = 0.74). In (b,c and d), the y-axis is set in log-10 scale.

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  Figure 4. Electrostatic interactions between the compounds and their binding pocket. The amino acid residues M51, K75 and A477 within the binding pocket are shown in the crystal structures in complex with (a), NS309 (PDB code, 4J9Z) (b), SKS-11 (PDB code, 5WBX) (c), SKS-14 (PDB code, 5WC5) (d), 1-EBIO (PDB code, 4G28), respectively. (e) The distances between the main chain oxygen of M51, the main chain oxygen of A477, the side chain nitrogen of K75 and the compounds.

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  Figure 5. Electrostatic Eint between the compounds and amino acid residues in their binding pocket. (a) The electrostatic Eint between the compounds and M51. (b) The electrostatic Eint between the compounds and K75. (c) The electrostatic Eint between the compounds and A477. (d) NS309 forms strong electrostatic interactions with three residues M51, K75 and A477.