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Figure 3.
Fig. 3. Conformational changes generate the heterodimer
interface. (A) The structure of the Ffh NG domain with GMPPNP
bound (1JPJ [PDB]
.pdb) (in lighter colors) is superimposed with its structure in
the complex. The N domain moves as a rigid body toward helix
 3 of the G
domain; this shift, in turn, is coupled to conformational
rearrangement in the DGQ motif at the N terminus of 3,
enabling formation of the extensive heterodimeric contact there.
Helix 4 moves with the
N domain, accommodated by an  2.9 Å
translation of the remainder of helix 3. Note the
concurrent reorientation of the C-terminal helix. (B) G-domain
conformational changes associated with complex formation are
limited to the loops of conserved sequence motifs. The magnitude
of the shifts are mapped so that the largest shifts ( 6.5
Å) are the darkest shaded regions. (C) Reorientation of
motifs II and III upon complex formation. The left panel shows
the Ffh NG GMPPNP structure, the right panel Ffh NG in the
complex. The side chain of motif III residue Leu192 moves to
insert into a pocket across the heterodimer interface, between
the guanine base and Gly259(249) that follows motif IV. Movement
of this leucine and the accompanying rearrangement of the motif
III backbone allows the P-loop to open sufficiently to
accommodate the nucleotide in an extended conformation (10).
Motif II residues Asp135 and Arg138 move into the catalytic
chamber. The same configuration is observed in FtsY.
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