Structure of (Na+,K+)-ATPase as revealed by electron microscopy and image processing

Area of Science:

• Biochemistry
• Structural Biology
• Membrane Proteins

Background:

• The (Na+,K+)-ATPase (sodium-potassium pump) is crucial for maintaining cellular ion gradients.
• Understanding its structure is key to elucidating its function and related diseases.
• Previous structural studies were limited by crystallization challenges.

Purpose of the Study:

• To determine the high-resolution structure of (Na+,K+)-ATPase.
• To identify optimal conditions for enzyme crystallization.
• To investigate the enzyme's monomeric and dimeric forms and the location of its alpha subunit.

Main Methods:

• Electron microscopy of negatively stained and freeze-dried/shadowed crystalline sheets.
• Induction of crystal formation using inorganic salts.
• Partial proteolysis of the alpha subunit with trypsin.
• Image processing and mass distribution analysis.

Main Results:

• Identified new conditions for optimal crystal formation of (Na+,K+)-ATPase.
• Observed two crystal forms: monomer and dimer in the unit cell, both sharing the same monomer structure.
• Tentatively identified the alpha subunit's location within the monomer through proteolysis studies.
• Demonstrated crystallization of partially proteolyzed enzyme under similar conditions.

Conclusions:

• Established novel methods for crystallizing (Na+,K+)-ATPase, enabling detailed structural analysis.
• Provided insights into the quaternary structure and subunit organization of the sodium-potassium pump.
• Highlighted structural similarities between (Na+,K+)-ATPase and calcium-ATPase, suggesting conserved structural motifs.