The capillarity picture and the kinetics of one-dimensional protein folding

Energy landscape theory unites the study of protein folding with the theory of phase transitions. Dimensionality, whose key role in phase transitions is well known, comes to the fore in folding repeat proteins. Repeat proteins are made of near repetitions of 20–40 residues encoding recurring structural motifs. Each repeating element interacts only with its immediate neighbors, forming extended, globally one-dimensional structures that can be interrupted by thermally excited defects (1). The equilibrium properties of repeat proteins may be mapped onto a one-dimensional Ising model (2–4). Going beyond equilibrium, in this issue of PNAS, Werbeck et al. (5) delight us by studying the folding kinetics of a very long repeat protein, D34, a 12-ankyrin repeat fragment of AnkyrinR.