Entropy and Barrier-Controlled Fluctuations Determine Conformational Viscoelasticity of Single Biomolecules

¹ University of Leeds

^* To whom correspondence should be addressed. E-mail: t.c.b.mcleish{at}leeds.ac.uk.

Submitted on September 18, 2006
Revised on October 31, 2006
Accepted on 9 November 2006

	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), using a generic model of biopolymer viscoelasticity that includes local `internal' conformational dissipation. Comparing two biopolymers, dextran and cellulose, polysaccharides with and without local bistable transitions, demonstrates that a signature of simple conformational change are minima in both the elasticity and internal friction around a characteristic force. A novel analysis of dynamics on a bistable energy landscape provides a simple explanation; an elasticity driven by the entropy, and friction by a barrier-controlled hopping time of populations between states, which is surprisingly distinct to the well-known relaxation time. This non-equilibrium microscopic analysis thus provides a means of quantifying new dynamical features of the energy landscape of the glucopyranose ring, revealing an unexpected underlying roughness and information on the shape of the barrier of the chair-boat transition in dextran. The results presented herein, provide a basis towards understanding the viscoelasticity of more complex macromolecular conformational transitions such as protein folding.

Key Words: Elasticity, Energy Landscape, Internal Friction, Non-Equilibrium Statistical Physics, Polymer Physics, Polysaccharides