Figure 3.
Cα trace of superposed homodimers of apo-CcpA (blue) and CcpA–(HPr-Ser46-P)–DNA (red, PDB code 1rzr). Superposition was performed with respect to the C-terminal subdomains (Csub) of CcpA. The twofold axis is in the vertical direction. (a) clearly shows the loss of contact between the N-terminal subdomains (Nsub), which exhibit a more open conformation in apo-CcpA (blue) compared with the ternary complex. In (b) CcpA is rotated around the dimer axis by about 90° to show the differences in the orientation of the DNA-binding domains (Dbd). Note also the cleft between the N- and C-subdomains, which is the small-molecule effector-binding site of the LacI-GalR family.