Single Molecule Force Spectroscopy on Polysaccharides by Atomic Force Microscopy

TLDR

Recent advances in piconewton instrumentation enable manipulation of single molecules and measurement of both intermolecular and intramolecular forces. Dextran filaments covalently linked to gold were vertically stretched with an AFM tip, and the reversible conformational change observed was confirmed by molecular dynamics simulations. At low forces dextran deformation follows the Langevin function with a 6‑Å Kuhn length; at higher forces the strand elongation is driven by bond‑angle twists, a reversible conformational change that stiffens the polymer and makes its elasticity dominated by bond‑angle bending.

Abstract

Recent developments in piconewton instrumentation allow the manipulation of single molecules and measurements of intermolecular as well as intramolecular forces. Dextran filaments linked to a gold surface were probed with the atomic force microscope tip by vertical stretching. At low forces the deformation of dextran was found to be dominated by entropic forces and can be described by the Langevin function with a 6 angstrom Kuhn length. At elevated forces the strand elongation was governed by a twist of bond angles. At higher forces the dextran filaments underwent a distinct conformational change. The polymer stiffened and the segment elasticity was dominated by the bending of bond angles. The conformational change was found to be reversible and was corroborated by molecular dynamics calculations.