Helix-coil and beta sheet-coil transitions in a simplified, yet realistic protein model

A reduced model of polypeptide chains and protein stochastic dynamics is employed in Monte Carlo studies of the coil-globule transition. The model assumes a high-resolution lattice representation of protein conformational space. The interaction scheme is derived from a statistical analysis of structural regularities seen in known three-dimensional protein structures. It is shown that model polypeptides containing residues that have strong propensities towards locally expanded conformations collapse to β-like globular conformations, while polypeptides containing residues with helical propensities form globules of closely packed helices. A more cooperative transition is observed for β-type systems. It is also demonstrated that hydrogen bonding is an important factor for protein cooperativity, although, for systems with suppressed hydrogen bond interactions, a higher cooperativity of β-type proteins is also observed.