αI-spectrin represents evolutionary optimization of spectrin for red blood cell deformability

Area of Science:

• Erythrocyte biology
• Molecular evolution
• Biophysics

Background:

• Spectrin tetramers in erythrocyte membranes are crucial for red blood cell survival.
• Mammalian αI-spectrin evolved from an ancestral gene, exhibiting moderate affinity for βI-spectrin.
• αII-spectrin in nonerythroid cells has higher affinity for βI-spectrin, hypothesized to aid membrane deformation.

Purpose of the Study:

• To investigate the role of spectrin tetramer affinity in erythrocyte membrane deformability.
• To test the hypothesis that adaptation of spectrin tetramer formation allows for rapid make and break for membrane accommodation.
• To generate mice with high-affinity spectrin tetramers by modifying αI-spectrin.

Main Methods:

• Generation of mice with high-affinity spectrin tetramers by exchanging tetramer formation sites.
• Analysis of erythrocyte hematologic parameters, thermostability, and membrane deformability.
• Assessment of membrane skeleton stability and remodeling under deformation using low shear forces.

Main Results:

• Erythrocytes with high-affinity αIIβI spectrin showed normal hematologic parameters but increased thermostability.
• These erythrocytes exhibited significantly reduced membrane deformability, displaying tumbling instead of tank treading under shear stress.
• The αIIβI membrane skeleton was more stable and showed less remodeling compared to wild-type mice.

Conclusions:

• Spectrin tetramer remodeling occurs in intact erythrocytes and is essential for normal membrane deformability.
• αI-spectrin represents an evolutionary optimization for tetramer formation in red blood cells.
• Neither excessively high nor low spectrin affinity supports the membrane properties needed for efficient oxygen transport.