Entropy and Barrier-Hopping Determine Conformational Viscoelasticity in Single Biomolecules

TL;DR

This study investigates how entropy and barrier-hopping influence the viscoelastic behavior of single biomolecules, revealing how conformational changes affect elasticity and internal friction through a microscopic energy landscape model.

Contribution

It introduces a generic biopolymer viscoelasticity model that incorporates internal conformational dissipation and links microscopic energy landscape features to macroscopic viscoelastic properties.

Findings

Identifies minima in elasticity and internal friction at specific forces related to conformational transitions.

Demonstrates that barrier-controlled hopping explains internal friction dynamics.

Reveals slow dynamics indicative of a rough energy landscape.

Abstract

Biological macromolecules have complex and non-trivial energy landscapes, endowing them a unique conformational adaptability and diversity in function. Hence, understanding the processes of elasticity and dissipation at the nanoscale is important to molecular biology and also emerging fields such as nanotechnology. Here we analyse single molecule fluctuations in an atomic force microscope (AFM) experiment using a generic model of biopolymer viscoelasticity that importantly includes sources of local `internal' conformational dissipation. Comparing two biopolymers, dextran and cellulose, polysaccharides with and without the well-known `chair-to-boat' transition, reveals a signature of this simple conformational change as minima in both the elasticity and internal friction around a characteristic force. A calculation of two-state populations dynamics offers a simple explanation in terms of an elasticity driven by the entropy, and friction by barrier-controlled hopping, of populations on a landscape. The microscopic model, allows quantitative mapping of features of the energy landscape, revealing unexpectedly slow dynamics, suggestive of an underlying roughness to the free energy.