Fig. 1.

(A) Structure of the 12 helices that form the TR 482 to 889 [Protein Data Bank (PDB) 1xwx]. Color coding: blue, N terminus; green, middle; and red, C terminus. VBS helices are numbered and represented with cartoon models, and the rest of the protein is shown with tube models. (B) Under the application of a force in the direction indicated by the black arrows in (A), TR starts to unfold. Once helix 12 exposed its VBS, Vh (PDB 1u6h), represented in yellow, reorganizes to bind to it. (C) X-ray structure of the complex Vh-VBS-helix 12, PDB 1u6h. Images were generated by using the VMD (Visual Molecular Dynamics) program (www.ks.uiuc.edu/research/vmd/).