Figure 1.
P−Pro coupled folding and binding scheme. P−Pro exhibits three-state folding with unfolded (U), partially folded intermediate (I), and folded (F) states. Folding is strongly coupled to the binding of two pyrophosphate ligands (L). Pyrophosphate may be bound at the α-site (Lα), β-site (Lβ), or both sites (L2) in any state. Unoccupied binding sites in U and I are reflected as undetectably weak affinities in the fits of the data. Species that remain unpopulated in 0 – 1 mM PPi —as revealed by fits of the data—and their associated transitions are indicated in gray. Conformational selection pathways are shown in blue, induced fit pathways in red, and mixed pathways in green.