Structure and Inhibition of the Human Na⁺/H⁺ Exchanger SLC9B2

Area of Science:

• Biochemistry
• Structural Biology
• Membrane Transport

Background:

• The sodium/proton exchanger NHA2 (SLC9B2) plays a crucial role in physiological processes including insulin secretion and blood pressure regulation.
• NHA2 exhibits a distinct 14-transmembrane helix structure, differing from other SLC9A/NHE members.
• Its homodimeric assembly is influenced by an additional N-terminal helix.

Purpose of the Study:

• To determine the high-resolution cryo-electron microscopy structures of human NHA2.
• To investigate the binding of the inhibitor phloretin and phosphatidic acid (PA) lipids.
• To elucidate the structural basis for NHA2 function and inhibition.

Main Methods:

• Cryo-electron microscopy (cryo-EM) at 2.8-2.9 Å resolution.
• Structural analysis of apo human NHA2, NHA2-Fab complex, and NHA2-phloretin complex.
• Biochemical assays to study lipid and inhibitor interactions.

Main Results:

• Detailed structures of human NHA2 in apo and inhibitor-bound states were obtained.
• Phosphatidic acid (PA) lipids were observed to bind at the homodimer interface, suggesting a regulatory role in cell volume.
• A key salt bridge interaction (D278-R432) at the ion binding site was identified, differing from previous bison NHA2 structures.

Conclusions:

• The human NHA2 structure provides a detailed molecular understanding of its unique architecture and homodimerization.
• PA lipid binding suggests a novel regulatory mechanism linked to cell volume.
• The structure in complex with phloretin serves as a valuable template for developing targeted NHA2 inhibitors for therapeutic applications.