The frequency-domain method reveals the dimeric structure of Na,K-ATPase

Area of Science:

• Biochemistry
• Molecular Biology
• Membrane Protein Structure

Background:

• The Na,K-ATPase enzyme is crucial for maintaining cellular ion gradients.
• Understanding the structural organization of the Na,K-ATPase, particularly the role of its β subunits, is vital for elucidating its function.
• Previous studies have proposed various models for the Na,K-ATPase complex.

Purpose of the Study:

• To determine the precise location and spatial arrangement of the β subunits within the native Na,K-ATPase complex.
• To investigate the functional quaternary structure of the Na,K-ATPase.
• To provide insights into the molecular mechanisms of ion transport.

Main Methods:

• Förster resonance energy transfer (FRET) measurements were employed.
• Lucifer yellow (donor) and lissamine rhodamine sulfonyl hydrazine (receptor) were used as fluorescent probes.
• The probes were covalently attached to the β subunits of the Na,K-ATPase from pig kidney.

Main Results:

• The β subunits are part of a single functional complex, suggesting the dimer (αβ)2 is the functional unit of Na,K-ATPase.
• The β subunits within the membrane-bound enzyme complex are spatially separated, not adjacent.
• The distance between fluorophores attached to the β subunits was measured to be 5.3 nm.

Conclusions:

• The functional unit of Na,K-ATPase is likely the (αβ)2 dimer.
• The β subunits are well-separated within the functional complex, indicating a specific structural arrangement.
• These findings contribute to a deeper understanding of Na,K-ATPase structure-function relationships.