Clamp loader interactions to open the sliding clamp. (a) The clamp is held in a distorted conformation. In the top panel, displacement vectors compared from the closed planar structure (PDB code 1CZD)  to that of the open form (PDB code 3U60)  are mapped out onto the structure and are scaled up by a factor of 4 and color coded blue to red. In the bottom panel, the relative domain rotations from the closed planar structure to the open conformation are mapped onto the schematic, with the vector length and width scaled by the magnitude of rotation. Figures adapted from . (b) Clamp loader contacts to the open sliding clamp. All five clamp loader subunits contact the open clamp. In the top panel, the clamp-interacting motifs of the clamp loader are shown with the rest of the structure displayed as a wireframe for clarity. In the bottom schematic diagram, the clamp loader AAA+ modules and the sliding clamp are shown from the side and flattened out onto the page so that all subunits can be viewed simultaneously. The contacts between the ATPs and arginine fingers direct the clamp loader to form a spiral assembly in which the AAA+ modules are arranged to perfectly match the symmetrically positioned binding clefts on the sliding clamp. Figure adapted from .
Kelch et al. BMC Biology 2012 10:34 doi:10.1186/1741-7007-10-34