Figure 3.

Assembly of CHIP monomers suggests that HH domains dimerize first. (A) CHIP assembly models. Upper/Lower rows show models where the corresponding HH/U-box dimers have been aligned as in the CHIP crystal for the bent, straight and chimeric monomers. Highlights in the lower row show structural clashes for bent and straight monomers and a mismatch for the chimeric dimer where the hydrophobic regions of the HH domains are on the outside. All the models are constructed using PyMOL 1.7. Mesh colors are as in Fig. 1. Representative MDS of HH-dimer-first models: (B) backbone RMSD of the U-box dimer relative to the crystal structure shows that the U-boxes from straight-dimer model does not dimerize; (C) Backbone RMSD of residues 146–166 in H7 for each protomer relative to their helical structure in the straight monomer (Fig. 2B) shows that the bent-dimer model does not form an extended H7; (D) TPR/U-box separation between Cα of residues TPR_R141 and U-box_E239, which interact in the bent monomer complex (Fig. 2A), shows that the straight-dimer never forms this complex and the bent-dimer never breaks them, whereas the chimeric-dimer breaks one complex and keeps the second intact, resembling the asymmetric structure of CHIP.