Ion permeation through the Na+,K+-ATPase

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• P-type ATPase pumps are crucial for maintaining cellular ion gradients.
• These pumps utilize a polar transmembrane pathway with regulated gates for ion transport.
• The Na+,K+-ATPase is a vital ion pump found in nearly all cells.

Purpose of the Study:

• To elucidate the ion pathway through the Na+,K+-ATPase.
• To investigate the structural and charge-selectivity properties of the pump's pathway.
• To understand the role of specific residues in ion coordination and selectivity.

Main Methods:

• Utilized the marine toxin palytoxin to uncouple the Na+,K+-ATPase gates.
• Employed small, hydrophilic, thiol-specific reagents as extracellular probes.
• Introduced cysteine residues along the anticipated cation pathway to monitor reagent reactions.

Main Results:

• Identified a wide outer vestibule leading to a narrowed pathway with a charge-selectivity filter.
• Demonstrated that conserved acidic residues coordinate ions and are critical for cation selectivity.
• Showed that reversing the charge of a single acidic residue converts the pathway to anion selectivity.

Conclusions:

• The Na+,K+-ATPase pathway features an accessible vestibule and a charge-selective filter.
• Specific acidic residues are essential for cation binding and transport, dictating pathway selectivity.
• Structural similarities suggest analogous cation exchange pathways in other P-type ATPases (Ca2+, H+,K+-ATPases).