Functional role of transient conformations: Rediscovering "chronosteric effects" thirty years later.

Proteins are dynamic entities that exert, in some cases, their functions via complex pathways, involving active transient species. This phenomenon was highlighted for the first time in 1983 by Antonini et al. (J. Biol. Chem. 258, 4676-4678), who demonstrated that at least one intermediate occurring in the formation of the bovine β-trypsin-Kunitz inhibitor complex displayed catalytic properties different from those of the active enzyme and of the inactive enzyme-inhibitor adduct. Since it was impossible to explain this phenomenon in terms of static three-dimensional structures, the term "chronosteric effects" was coined to capture the observation that transient species are relevant to protein function(s). Here, some recent results on the folding and function of proteins are reported on the light of chronosteric effects.