Polyamine blockade and binding energetics in the MthK potassium channel

Area of Science:

• Molecular Biology
• Biophysics
• Ion Channel Physiology

Background:

• Polyamines (spermidine, spermine) are cellular cations regulating K+ efflux.
• They bind voltage-dependently to inwardly rectifying K+ (Kir) channels.
• The precise physical interactions and voltage dependence of polyamine blockade remain unclear.

Purpose of the Study:

• To elucidate the polyamine-blocking mechanism in the MthK channel.
• To investigate the physical interactions between polyamines and the MthK channel pore.
• To understand the basis of voltage-dependent polyamine blockade.

Main Methods:

• Electrophysiology to measure ion channel currents.
• Computational analysis of polyamine-channel interactions.
• Molecular simulations of the MthK pore with spermidine and spermine.

Main Results:

• Spermidine (SPD3+) and spermine (SPM4+) exhibit voltage-dependent blockade of MthK channels.
• Both polyamines access a blocking site with similar gating valences.
• SPM4+ binds with higher affinity than SPD3+ due to distinct electrostatic interactions.
• Molecular simulations show polyamine interaction with T59 at the selectivity filter, coupled to K+ ion movement.

Conclusions:

• The study clarifies the voltage-dependent blockade mechanism of polyamines in K+ channels.
• Coupled movement of polyamines and K+ ions contributes significantly to voltage dependence.
• Differences in polyamine binding affinity are attributed to specific electrostatic interactions within the MthK pore.