Atomic force microscopy of the erythrocyte membrane skeleton

Area of Science:

• Cell biology
• Biophysics
• Materials science

Background:

• The erythrocyte membrane skeleton provides structural integrity to red blood cells.
• Understanding its organization is crucial for comprehending cell mechanics and disease.
• Previous imaging techniques had limitations in resolving the native structure.

Purpose of the Study:

• To visualize the human erythrocyte membrane skeleton using atomic force microscopy (AFM).
• To investigate the effects of fixation, drying, and substrate interactions on skeleton structure.
• To assess the role of spectrin and actin in the observed meshwork.

Main Methods:

• Human erythrocytes were prepared and opened to expose the cytoplasmic membrane face.
• Atomic force microscopy (AFM) was used to image unfixed and fixed membranes under aqueous and air-dried conditions.
• Erythrocyte ghosts were treated to extract membrane proteins (spectrin, actin) and the lipid bilayer.

Main Results:

• AFM revealed an irregular meshwork of the membrane skeleton with varied opening sizes (35-100 nm).
• Air-drying and attachment to polylysine-coated substrates promoted spectrin aggregation.
• Extraction of spectrin and actin largely removed the observed meshwork structures.
• Triton X-100 treatment revealed aggregated components in the remaining skeleton.

Conclusions:

• The erythrocyte membrane skeleton forms a complex meshwork primarily composed of spectrin and actin.
• Spectrin tetramers exist in a more compact state within the cell than their contour length suggests.
• AFM is a valuable tool for imaging the erythrocyte membrane skeleton under near-physiological conditions.