α-Helix Unwinding as Force Buffer in Spectrins

Area of Science:

• Cell biology
• Biophysics
• Structural biology

Background:

• Spectrins are essential cytoskeletal proteins located at the plasma membrane.
• They connect membrane anchors to the actin cortex and actin filaments.
• Spectrins play a critical role in cell deformation due to their unique structure.

Purpose of the Study:

• To investigate the mechanical stability and force buffering capabilities of spectrin.
• To elucidate the molecular mechanisms underlying spectrin's response to mechanical stress.

Main Methods:

• High-speed force spectroscopy was employed to measure spectrin's mechanical properties.
• Steered molecular dynamics simulations were used to analyze spectrin's behavior at the molecular level.

Main Results:

• Spectrin functions as a soft spring at short extensions (70-100 Å).
• Under continuous stretching, spectrin's α-helices unwind, exhibiting a viscous mechanical response (100-300 Å).
• This force buffering arises from the dynamic disruption and reformation of α-helical hydrogen bonds.

Conclusions:

• Unlike β-sheet proteins that unfold catastrophically, α-helical spectrins dominantly unwind.
• Spectrin provides a viscous force buffer, extending up to five times its folded length.
• This unwinding mechanism is vital for cellular mechanical stability during deformation.