Ion-binding properties of a K+ channel selectivity filter in different conformations

Area of Science:

• Biophysics
• Molecular Biology
• Ion Channel Function

Background:

• Potassium (K+) channels are crucial membrane proteins regulating ion transport.
• Voltage-gated K+ (KV) channels possess two gates: one for opening and one for C-type inactivation.
• The KcsA channel from Streptomyces lividians serves as a model for studying K+ channel inactivation.

Purpose of the Study:

• To investigate the ion-binding properties of K+ channels in different conformational states.
• To determine the structural differences between conductive, inactivated, and constricted K+ channel filters.
• To explore the influence of lipid bilayers on the intracellular gate of K+ channels.

Main Methods:

• Isothermal titration calorimetry (ITC) to measure equilibrium ion-binding.
• Electron paramagnetic resonance (EPR) spectroscopy to assess the intracellular gate's state.
• Utilizing KcsA channel variants, including a semisynthetic channel incapable of filter constriction.

Main Results:

• K+ ion binding differs significantly between conductive/inactivated and constricted selectivity filters.
• The intracellular gate's conformation is influenced by the presence or absence of a lipid bilayer.
• Findings challenge the notion that a constricted filter is a prerequisite for K+ channel inactivation.

Conclusions:

• The structural states of K+ channel selectivity filters are distinct and correlate with different ion-binding characteristics.
• Lipid-protein interactions play a role in regulating K+ channel gating.
• This research provides new insights into the mechanisms of K+ channel function and inactivation.