# Dynamic transition from $\alpha$-helices to $\beta$-sheets in polypeptide superhelices

## TL;DR

This study investigates the mechanical behavior of protein superhelices under force, revealing a transition from alpha-helices to beta-sheets that influences their deformation and can inform the design of new biomaterials.

## Contribution

The paper introduces a theoretical model based on phase transition principles to describe the mechanical and kinetic properties of protein superhelices under non-equilibrium conditions.

## Key findings

- All superhelices exhibit elastic, plastic, and inelastic regimes under stretch.
- A dynamic alpha-to-beta transition marks the onset of plastic deformation.
- Scaling laws enable rational design of materials with specific mechanical properties.

## Abstract

We carried out dynamic force manipulations $in$ $silico$ on a variety of superhelical protein fragments from myosin, chemotaxis receptor, vimentin, fibrin, and phenylalanine zippers that vary in size and topology of their $\alpha$-helical packing. When stretched along the superhelical axis, all superhelices show elastic, plastic, and inelastic elongation regimes, and undergo a dynamic transition from the $\alpha$-helices to the $\beta$-sheets, which marks the onset of plastic deformation. Using Abeyaratne-Knowles formulation of phase transitions, we developed a theory to model mechanical and kinetic properties of protein superhelices under mechanical non-equilibrium conditions and to map their energy landscapes. The theory was validated by comparing the simulated and theoretical force-strain spectra. Scaling laws for the elastic force and the force for $\alpha$-to-$\beta$ transition to plastic deformation can be used to rationally design new materials of required mechanical strength with desired balance between stiffness and plasticity.