Nonlinear elasticity of an alpha -helical polypeptide

Area of Science:

• Biophysics
• Polymer Physics
• Structural Biology

Background:

• Polypeptides with alpha-helical secondary structures are fundamental biological molecules.
• Understanding their mechanical properties under stress is crucial for elucidating protein function.
• Existing models often simplify the complex interplay between secondary structure and chain dynamics.

Purpose of the Study:

• To develop a minimal model extending the wormlike chain concept for polypeptides with alpha-helical secondary structure.
• To investigate the extensional and bending compliance of alpha-helices under various mechanical loads.
• To analyze the nonlinear interactions between forces and torques on these molecules.

Main Methods:

• A modified wormlike chain model incorporating a scalar variable for secondary structure.
• Calculation of extensional compliance under tensile stress.
• Computation of bending compliance under imposed torques.
• Analysis of nonlinear force-torque interactions.

Main Results:

• The model predicts highly nonlinear responses due to the coupling of secondary structure variables with conformational degrees of freedom.
• A distinct lengthening transition was observed under applied force.
• A buckling transition was identified under applied torque.

Conclusions:

• The developed model accurately captures the complex mechanical behavior of alpha-helical polypeptides.
• The inherent bistability of these structures may play a significant role in protein conformational changes in vivo.
• This work provides a framework for understanding the mechanical basis of protein dynamics.