Stretching of proteins in the entropic limit.

Mechanical stretching of six proteins is studied through molecular dynamics simulations. The model is Go-like, with Lennard-Jones interactions at native contacts. Low-temperature unfolding scenarios are remarkably complex and sensitive to small structural changes. Thermal fluctuations reduce the peak forces and the number of metastable states during unfolding. The unfolding pathways also simplify as temperature rises. In the entropic limit, all proteins show a monotonic decrease of the extension where bonds rupture with their separation along the backbone (contact order).