Fig. 1.

Nucleation–condensation mechanism of protein folding (Abkevich et al., 1994; Fersht, 1995, 1997, 1999; Nölting et al., 1997; Fersht & Sato, 2004; Jemth et al., 2005; Galzitskaya et al., 2005): folding is initiated by the formation of a folding nucleus which has some correct secondary and tertiary structure interactions so that further structure can rapidly condense onto this nucleus. This nucleus with marginal stability dramatically reduces the number of conformations which have to be sampled in the following folding steps.