Treatment of disulfide bonds in coarse-grained UNRES force field

Disulfide bonds, despite the advances of the computational methods, are underrepresented in theoretical chemistry and the role of disulfide bonds is of ten diminished in bioinformatical studies. Most of the molecular modeling tools do not allow studying the process of disulfide bond formation and breaking, which is equally important as the sole presence of disulfide bonds in proteins and peptides. The UNRES (UNited RESidue) coarse-grained force field allows treating disulfide bonds in two ways: as static (formed or broken in the simulation) or dynamic (all specified cysteine residues can form and break disulfide bonds during simulation). The comparison between those two approaches of disulfide-bond treatment is presented for protein folding on the example of four small β - and α + β proteins with one, two, three and four disulfide bonds. The results clearly show that proper disulfide bond treatment is important in simulations and significantly enhances the quality of folded structures.