β‐Sheet coil transitions in a simple polypeptide model

A simplified model of a polypeptide chain is used to study the dynamics of the β‐sheet–coil transition. Each amino acid residue is treated as a single quasiparticle in an effective potential that approximates the potential of mean force in solution. The model is used to study the equilibrium and dynamic aspects of the sheet–coil transition. Systems studied include ones with both strands free to move (two‐strand sheet), and ones with either strand fixed in position (multistrand sheet). The equilibrium properties examined include sheet–coil equilibrium constants and their dependence on chain position. Dynamic properties are investigated by a stochastic simulation of the Brownian motion of the chain in its solvent surroundings. Time histories of the dihedral angles and residue–residue cross‐strand distances are used to study the behavior of the sheet structure. Auto‐and cross‐correlation functions are calculated from the time histories with relaxation times of tens to hundreds of picoseconds. Sheet–coil rate constants of tens of ns−1 were found for the fixed strand cases.

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