FIGURE 2.

2.4 Å X-ray crystal structure of the Shigella T3SS ATPase Spa47. A, crystal structure of Spa47^Δ1–79 with coloration corresponding to the predicted domains highlighted in the bar diagram of the Spa47 sequence, where the truncated N-terminal oligomerization domain is represented by a thick dashed line and the black-shaded region corresponds to the N-terminal residues of the construct that are not included in the structure. The gray portion of the Spa47 structure corresponds to the catalytic ATPase domain, the cyan region represents the C-terminal domain, and the Walker A (P-loop) and B motifs are shown in red and blue, respectively. The secondary structure elements are identified, and the dashed lines within the Spa47 structure represent disordered regions with unassigned structure (four N-terminal residues and those connecting α6-β7 and α8-β10). β9 is located directly behind β10 and not visible in this orientation. B and C, alignment of Spa47 (gray) with the catalytic ATPase and C-terminal domains of FliI (green, B) and EscN (blue, C) illustrates the high degree of conservation within the catalytic core of the related ATPases, especially within the nucleotide-binding region (black boxes). D, a closer view of the nucleotide binding site within the aligned structures identifies the conserved active site Lys¹⁶⁵ and Glu¹⁸⁸ residues positioned near the FliI-bound ADP shown with a yellow carbon skeleton. The PDB codes for the Spa47, FliI, and EscN structures are 5SWJ, 2DPY, and 2OBM, respectively. The crystal structures were rendered using PyMOL.