'Chair-boat' transitions and side groups affect the stiffness of polysaccharides

Atomic force microscopy experiments with individual beta-(1,4)-glucose poly mers (cellulose) and alpha-(1,4)-glucose polymers (amylose) have been simul ated by molecular dynamics stretching simulations, and force/extension curv es were calculated. For forces above 1200 pN, we predict a stiffness of 510 0 pN/Angstrom for both polymers. In contrast to beta-glucose, alpha-glucose exhibits increased flexibility in the 300-1200 pN range, which our simulat ions attribute to conformational 'chair-boat' transitions of the alpha-gluc ose monomers. For beta-glucose no such transitions were seen. We suggest a mechanism of neighbor inhibition, which should allow the tailoring of elast ic properties through modification of inter-monomeric rotational flexibilit y, e.g., by introducing or removing bulky or charged side groups. (C) 1999 Elsevier Science B.V. All rights reserved.