Conformational Collapse of Surface-Bound Helical Filaments

TL;DR

This paper demonstrates a phase transition in surface-bound chiral polymers with intrinsic twist, where increased binding affinity causes a shift from a stiff, untwisted state to a flexible, twisted state with many twist walls, affecting their biological and experimental behavior.

Contribution

It reveals a sharp phase transition driven by binding strength in surface-bound helical filaments with anisotropic stiffness, highlighting the role of twist walls in conformational flexibility.

Findings

Above critical binding strength, filaments are stiff and untwisted.

Below critical binding strength, twist walls proliferate, reducing persistence length.

The transition depends solely on torsional modulus and intrinsic twist rate.

Abstract

Chiral polymers are ubiquitous in nature and in the cellular context they are often found in association with membranes. Here we show that surface bound polymers with an intrinsic twist and anisotropic bending stiffness can exhibit a sharp continuous phase transition between states with very different effective persistence lengths as the binding affinity is increased. Above a critical value for the binding strength, determined solely by the torsional modulus and intrinsic twist rate, the filament can exist in a zero twist, surface bound state with a homogeneous stiffness. Below the critical binding strength, twist walls proliferate and function as weak or floppy joints that sharply reduce the effective persistence length that is measurable on long lengthscales. The existence of such dramatically different conformational states has implications for both biopolymer function {\it in vivo} and for experimental observations of such filaments {\it in vitro}.