FIGURE 2.

Transitions between structures P_II^NO-COF and P_II^ADP3. A, organization of the T-loop structure in the ligand-free P_II trimer leads to an entirely flexible T-loop conformation. The P_II^NO-COF structure is shown in red as a schematic with a close-up view of the β-sheet core (β2, β3, β2*, and β3*). The H-bond interactions between terminal residues are marked by dotted lines. The terminal residues of the secondary structures are labeled. B, side view focusing on the S2 site of the trimeric superimposed P_II^NO-COF (red) and P_II^ADP3 (blue) complex structures. Residues that change their side-chain conformations are depicted, and changes are traced by green arrows. Secondary structure elements that significantly change their conformations upon ADP binding are marked with yellow dots (C terminus (CT), T-loop, and B-loop).