Mechanism of Na+/H+ antiporting.

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Na+/H+ antiporters are critical for maintaining cellular salt and pH balance.
• The transport mechanism and pH regulation of Escherichia coli NhaA remain incompletely understood despite its structural determination.

Purpose of the Study:

• To elucidate the atomically detailed mechanism of NhaA antiporter function and pH regulation.
• To propose a functional model for NhaA based on molecular dynamics simulations and experimental data.

Main Methods:

• Atomically detailed molecular dynamics simulations of NhaA.
• Integration of simulation data with existing experimental findings.
• Site-directed mutagenesis experiments for validation.

Main Results:

• A model for NhaA function was proposed, highlighting the roles of three conserved aspartate residues.
• Asp164 (D164) identified as the Na+-binding site.
• Asp163 (D163) controls site accessibility, and Asp133 (D133) is crucial for pH regulation.
• The mechanism requires two protons per transported Na+ ion, involving sequential protonation of D163 and D164.

Conclusions:

• The proposed model provides an atomic-level understanding of NhaA transport and pH-dependent gating.
• Mutagenesis studies validated the key roles of the identified aspartate residues in the proposed mechanism.