1. Department of Physiology and Biophysics, Rochester, Minnesota 55905, USA
2. Mayo Clinic Cancer Center and Department of Pharmacology, Mayo Foundation, Rochester, Minnesota 55905, USA

Correspondence to: Julio M. Fernandez¹ Correspondence and requests for materials should be addressed to J.M.F. (e-mail: Email: fernandez.julio@mayo.edu).

Abstract

Many common, biologically important polysaccharides contain pyranose rings made of five carbon atoms and one oxygen atom. They occur in a variety of cellular structures, where they are often subjected to considerable tensile stress^{1, 2, 3, 4, 5, 6}. The polysaccharides are thought to respond to this stress by elastic deformation, but the underlying molecular rearrangements allowing such a response remain poorly understood. It is typically assumed, however, that the pyranose ring structure is inelastic and locked into a chair-like conformation. Here we describe single-molecule force measurements^{7, 8, 9, 10, 11, 12} on individual polysaccharides that identify the pyranose rings as the structural unit controlling the molecule's elasticity. In particular, we find that the enthalpic component of the polymer elasticity^{10, 11, 12, 13, 14} of amylose, dextran and pullulan is eliminated once their pyranose rings are cleaved. We interpret these observations as indicating that the elasticity of the three polysaccharides results from a force-induced elongation of the ring structure and a final transition from a chair-like to a boat-like conformation. We expect that the force-induced deformation of pyranose rings reported here plays an important role in accommodating mechanical stresses and modulating ligand binding in biological systems.