Figure 3

The mADK lid domain dynamics. (a) Superposed crystal structures of mADK binary (blue) and ternary complex (orange). The lid domain moves 39.4° over the large domain, causing the transition between a fully open and a closed conformation. The Mg²⁺ (green spheres) and K⁺ (purple sphere) ions were observed only in the ternary closed complex. The substrates are shown as sticks with carbon, oxygen, nitrogen and phosphorus atoms colored as yellow, red, blue and orange, respectively. (b) Superposed mADK binary complex (blue) and apo T. brucei apo form structure (PDB code: 4N08) (yellow). The lid domains of both structures are in the fully open conformation. (c) Superposed lid domain of the binary (blue) and ternary mADK (orange) complexes. The rotation of the lid domain results in the translocation of Arg148 residue about the active site, being able to interact with the β-phosphate of the ADP (ADP not shown). The anion hole residues (DTNGAG) are shown in sticks in both complexes. The asterisk highlights the Asn314 that exhibit a different conformation at an open lid form (binary complex) in relation to closed lid domain (ternary complex). (d) Influence of the potassium ion on the ATP P-loop residues conformation (Glu303-Ile309), continuous segment to anion hole. The Glu305 residue shows a distinct conformation in the ternary complex leading to a different position of the ADP adenine ring.