Coupling between an electrostatic network and the Zn²⁺ binding site modulates Hv1 activation

Area of Science:

• Biophysics
• Ion Channel Physiology
• Structural Biology

Background:

• The voltage sensor (VS) domain of Hv1 proton channels controls voltage-dependent proton flow (G_AQ).
• Extracellular Zn²⁺ potently modulates this conductance, requiring specific histidine residues, but the binding site and mechanism remain unclear.

Purpose of the Study:

• To determine the atomic structure of the Zn²⁺ coordination site on Hv1.
• To elucidate the mechanism by which extracellular Zn²⁺ stabilizes a closed-state conformation.

Main Methods:

• Histidine mutagenesis to identify Zn²⁺-interacting residues.
• Experimental Zn²⁺-mapping to build a resting-state Hv1 model (Hv1 F).
• Molecular dynamics (MD) simulations to analyze Zn²⁺ coordination and conformational changes.

Main Results:

• Identified residues involved in Zn²⁺ binding and coordination through mutagenesis and MD simulations.
• Observed conformational coupling between the extracellular Zn²⁺ site and the intracellular Coulombic network (ICN).
• Mutating an ICN Glu residue (E153) shifted G_AQ activation and reduced Zn²⁺ potency.

Conclusions:

• Extracellular Zn²⁺ binding site structure and function elucidated.
• Zn²⁺ binding is conformationally coupled to the ICN, influencing VS activation.
• A general mechanism for ligand-modulated VS activation in ion channels is proposed.