Temperature- and Force-Induced beta-Sheet Unfolding in an Exactly Solvable Model

Abstract

The stability of a $β$-sheeted conformation and its transition into a random coil are studied with a 2D lattice biopolymer model. At low temperature and low external force, the polymer folds back and forth on itself and forms a $β$-sheet. Our analytical calculation and Monte Carlo simulation reveal that a co-operative $β$-sheet--random coil transition takes places when the temperature or force is increased, with a dramatic decrease in the contact number. These predictions are in good agreement with experiments on titin protein. This transition is not a real phase-transition, indicating that backbone hydrogen-bonding alone is unable to stabilize a distinct $β$-sheet phase.

13 pages with 4 ps figures. Revised version. A serious mistake in the original version was corrected and new simulation data were included