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 em ployed in Monte Carlo studies of the coil-globule transition. The model ass umes a high-resolution lattice representation of protein conformational spa ce. The interaction scheme is derived from a statistical analysis of struct ural regularities seen in known three-dimensional protein structures. It is shown that model polypeptides containing residues that have strong propens ities towards locally expanded conformations collapse to beta -like globula r conformations, while polypeptides containing residues with helical propen sities form globules of closely packed helices. A more cooperative transiti on is observed for beta -type systems. It is also demonstrated that hydroge n bonding is an important factor for protein cooperativity, although, for s ystems with suppressed hydrogen bond interactions, a higher cooperativity o f beta -type proteins is also observed.