Figure 2. Overall structure of AA-LCKS.

Cartoon diagram of the dimeric CMP-Kdo synthetase from Aquifex aeolicus (AA-LCKS). The CTP substrate is shown in both stick and transparent surface representation, Mg²⁺ ions are shown as green spheres. (A) Perspective highlighting the U-shaped arrangement of each protein molecule. The N-terminal domain binds the CTP substrate, whereas the C-terminal domain is responsible for Kdo binding and homodimer formation. The spatial orientation of the two domains leads to a central groove between them. (B) Top view onto the central groove. Panels (A) and (B) are related by the indicated rotation.