1. Catalytic Center Assembly of HPPK as Revealed by the Crystal Structure of a Ternary Complex at 1.25 Å Resolution 
Jaroslaw Blaszczyk, Genbin Shi, Honggao Yan, Xinhua Ji 
Structure 
Volume 8, Issue 10, Pages (October 2000)
DOI: /S (00)

2. Figure 1 HP and HP Analogs
Reaction of pyrophosphoryl transfer from ATP to HP catalyzed by HPPK, the first reaction in the folate biosynthetic pathway. HP analogs HP-1, HP-2 [7] and HP-3 [8] are also shown
Structure 2000 8, DOI: ( /S (00) )

3. Figure 2
The Overall Fold of HPPK and the Structure of the Bound HP and MgAMPCPP
(a) Apo-HPPK (orange, [2]) superimposed with the ternary complex HPPK–HP–MgAMPCPP (green, this work) showing the secondary-structure elements (α helices as spirals, β strands as arrows, and loops as tubes), substrate molecules, and Mg2+ ions (ball-and-stick models with atomic color scheme: carbon in black, nitrogen in blue, oxygen in red, phosphorus in pink, and magnesium in gray).
(b) Ball-and-stick model of HP–MgAMPCPP superimposed with the final 2Fo–Fc electron-density map contoured at 2.0σ. (The illustration was prepared with MOLSCRIPT [21] and Raster3D [22].)
Structure 2000 8, DOI: ( /S (00) )

4. Figure 3 Van der Waals Surface Representations of HPPK
(a) Apo-HPPK [2].
(b) HPPK–HP–MgAMPCPP (this work) illustrating the conformational differences between the two structures. The surface is colored according to electrostatic potential: blue for positive and red for negative. The substrate molecules and cofactors are represented as ball-and-stick models with the atomic color scheme (carbon in white, nitrogen in blue, oxygen in red, phosphorus in yellow, and magnesium in green). (This figure was prepared using the program GRASP [23].)
Structure 2000 8, DOI: ( /S (00) )

5. Figure 4 The Open and Closed Catalytic Center of HPPK
(a) The three uncoupled flexible loops of HPPK in the apo-enzyme [2].
(b) The coupling of these loops in the ternary complex. In the ternary complex, a hydrogen-bond network involves N10 from Loop-1; P47 and Q50 from Loop-2; and W89, P91, and R92 from Loop-3. This network is not observed in apo-HPPK. The orientation of the drawing is indicated by the position of the substrate molecules HP and MgAMPCPP. (This figure was prepared with the program MOLSCRIPT [21].)
Structure 2000 8, DOI: ( /S (00) )

6. Figure 5
Stereoviews Illustrating Detailed Protein–HP Interactions in HPPK–HP–MgAMPCPP
(a) Ball-and-stick models. Open bonds represent protein residues and filled bonds represent substrate molecules. The atomic color scheme is used (carbon in black, nitrogen in blue, oxygen in red and magnesium in yellow). Dotted lines represent electrostatic interactions.
(b) Cα trace alignment of HPPK in its complex form (blue) and its apo-form (red [2]). HP-interacting residues are shown as stick models. Residues without significant positional shift or conformational change, or both, are indicated with black labels, and residues with dramatic changes have colored labels (blue for the complex and red for the apo-enzyme).
(c) HP binding site alignment of E. coli HPPK (blue) and H. influenzae HPPK (purple [7]) with original residue numbers used. (The figure was prepared by using MOLSCRIPT [21].)
Structure 2000 8, DOI: ( /S (00) )

7. Figure 6
Stereoviews Illustrating Detailed Protein-MgAMPCPP Interactions in HPPK–HP–MgAMPCPP
(a) Ball-and-stick models. Open bonds represent protein residues and filled bonds representing substrate molecules. The atomic color scheme is used (carbon in black, nitrogen in blue, oxygen in red, phosphorus in pink and magnesium in yellow). Dotted lines represent electrostatic interactions.
(b) Cα trace alignment of HPPK in its complex form (blue) and apo-form (red, [2]). MgAMPCPP-interacting residues are shown as stick models. Residues without significant positional shift or conformational change, or both, are indicated with black labels. Residues with dramatic changes have blue and red labels for the complex and apo-enzyme, respectively.
(c) MgAMPCPP binding site alignment of the E. coli HPPK (blue) and H. influenzae enzyme (purple [7]) with original residue numbers and the same labeling style as in (b). (This figure was prepared by using MOLSCRIPT [21].)
Structure 2000 8, DOI: ( /S (00) )

8. Figure 7
Raster3D [22] Representation of the Adenine Specificity of HPPK
Protein residues and the ATP analog in HPPK–HP–MgAMPCPP are illustrated as ball-and-stick models using the atomic color scheme (carbon in black, nitrogen in blue, oxygen in red and phosphorous in purple). Protein residues and water molecules in apo-HPPK [2] are illustrated as transparent ball-and-stick models. Hydrogen bonds are represented as thin lines in both structures
Structure 2000 8, DOI: ( /S (00) )

9. Figure 8 ATP and ATP Analog
Schematic illustration of the protein–nucleotide interactions in (a) HPPK–HP–MgAMPCPP and (b) HPPK–HP-3–MgATP [8]. Hydrogen bonds are represented as dashed lines and the Mg2+ ion coordination as solid lines
Structure 2000 8, DOI: ( /S (00) )

10. Figure 9
The Associative Character of the Transition State of HPPK-Catalyzed Pyrophosphoryl Transfer
(a) The coordination of the two Mg2+ ions assists in creating the proper geometry for the one-step pyrophosphoryl transfer catalyzed by HPPK. A ball-and-stick model is used, with atomic color scheme (carbon in black, nitrogen in blue, oxygen in red, phosphorus in purple, and magnesium in gray). Thin, solid black lines depict the coordination of the two Mg2+ ions, and a dashed line is drawn between the hydroxyl of HP and the β-phosphorus of AMPCPP. (This illustration was prepared with MOLSCRIPT [21] and Raster3D [22].)
(b) Schematic illustration of the associative transition state of pyrophosphoryl transfer as suggested by the assembly of the active center observed in the ternary complex HPPK–HP–MgAMPCPP shown in (a)
Structure 2000 8, DOI: ( /S (00) )