Key result
Replacing K+ with Na+ caused shifts in the amide-I signal of the KcsA potassium channel, representing K+ binding to different sites in the selectivity filter with dissociation constants of 9 or 18 mM.
ATR-FTIR spectroscopy reveals distinct vibrational modes corresponding to K+ binding at different sites within the KcsA potassium channel selectivity filter.
No immediate clinical implications for ion channel disorders; leaves open extension to mammalian cardiac potassium channels.
The potassium channel is highly selective for K(+) over Na(+), and the selectivity filter binds multiple dehydrated K(+) ions upon permeation. Here, we applied attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy to extract ion-binding-induced signals of the KcsA potassium channel at neutral pH. Shifts in the peak of the amide-I signal towards lower vibrational frequencies were observed as K(+) was replaced with Na(+). These ion species-specific shifts deduced the selectivity filter as the source of the signal, which was supported by the spectra of a mutant for the selectivity filter (Y78F). The difference FTIR spectra between the solution containing various concentrations of K(+) and that containing pure Na(+) demonstrated two types of peak shifts of the amide-I vibration in response to the K(+) concentration. These signals represent the binding of K(+) ions to the different sites in the selectivity filter with different dissociation constants (KD = 9 or 18 mM).
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Furutani et al. (2012) studied this question. Potassium (K+) ions vs. Sodium (Na+) ions was evaluated on Peak shifts of the amide-I vibration. Replacing K+ with Na+ caused shifts in the amide-I signal of the KcsA potassium channel, representing K+ binding to different sites in the selectivity filter with dissociation constants of 9 or 18 mM.
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