Dominant forces in protein folding

T e purpose of this review is to assess the nature and mag-nitudes of the dominant forces in protein folding. Since proteins are only marginally stable at room temperature, ’ no type of molecular interaction is unimportant, and even small interactions can contribute significantly (positively or nega-tively) to stability (Alber, 1989a,b; Matthews, 1987a,b). However, the present review aims to identify only the largest forces that lead to the structural features of globular proteins: their extraordinary compactness, their core of nonpolar resi-dues, and their considerable amounts of internal architecture. This review explores contributions to the free energy of folding arising from electrostatics (classical charge repulsions and ion pairing), hydrogen-bonding and van der Waals in-teractions, intrinsic propensities, and hydrophobic interactions. An earlier review by Kauzmann (1959) introduced the im-