Figure 1.

Diagrams depicting protein ensembles and transitions between ensemble configurations. The horizontal axis, 'conformation coordinate' is a single dimension in a hypothetical energy landscape; the vertical axis is free energy, and the shaded areas represent regions of the landscape energetically accessible to the protein within the ensemble. (a) depicts a transition from a relatively narrow ensemble of structures about a dominant conformation, A, to a broader ensemble about the same conformation - a transition that might be triggered, for instance, by a decrease in protein concentration. (b) depicts a transition from a state dominated by conformation 'A', to a state in which two conformations, A and B are nearly equal in abundance. The apparent breadth of the ensemble increases in this transition. (c) depicts a change in state from one dominated by conformation 'A' to one dominated by conformation 'B'. Although the structure/conformation of the protein has changed, the apparent 'breadth' of the ensemble remains essentially unchanged.