CHIP folds into a symmetric dimer in the absence of TPR. (A) Truncated HH-chimeric-dimer (CHIP146–303) folds into a symmetric conformation similar to fCHIP in the absence of TPR domains (overlap backbone RMSD of 3.9 Å relative to PDB 2F42 shown in black). RMSD of interacting helices in the U-box dimer as a function of time for CHIP (magenta) and truncated CHIP (green) averaged over three independent runs. (B) Sketch of the free energy landscape of U-box dimerization in the presence (magenta) and absence (green) of TPR. CHIP dimerization triggers a repulsive barrier that prevents the U-boxes to properly align until after H7 breaks, and the TPR and U-box detach (dashed line). The snapping of H7 generates an out-of-equilibrium pathway that overcomes the thermodynamic barrier imposed by the TPR-U-box interaction. Approximate loci of specific structural transitions observed in the MDS dimerization trajectories in Fig. 4B,C and D are indicated: (I) dimer recognition, (II) breaking of helix 7, and (III) C-terminal insertion.