FIGURE 3.

Comparison of the functional dimer of wild type GlmS and of the inactive dimer of C1A-GlmS. A, functional dimer of the GlmS·Fru6P structure (PDB code 2BPL). The synthase and glutaminase domains are colored deep purple and pink, respectively, with the C-loop, forming the main part of the channel, highlighted in red. The Fru6P ligand and amino-terminal cysteine are shown as blue sticks. The distance between the C2 atom of Fru6P and the Sγ atom of Cys-1 is 16.6 Å. B, inactive dimer of the C1A-GlmS hexamer shown in the same orientation as in A. The synthase and glutaminase domains are colored blue and cyan, respectively, with the C-loop highlighted in red. The Glc6P and Glu ligands at the active sites are shown as cyan sticks, and Glc6P at the secondary sugar-binding site is shown as green sticks. The distance between the C2 atom of Glc6P bound at the synthase site and the Cδ atom of Glu bound at the glutaminase site is 33.2 Å. C, two orthogonal views of the superposition of the synthase domains of the GlmS·Fru6P and C1A-GlmS structures (same colors as in A and B) with a surface representation of the C1A-GlmS structure. After superposition of one synthase dimer of the C1A-GlmS and GlmS·Fru6P structures (root mean square deviation = 0.8 Å over 650 Cαs), the positions of the apex and inner glutaminase domains in the former structure (as shown in Fig. 1B) are related to those of the glutaminase domains in the latter structure by a 7.4 Å translation and 175.5° rotation and by a 1.1 Å translation and 91.9° rotation, respectively.