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Figure 2.
Fig. 2. An extensive interaction surface. (A) The molecular
surfaces of the Ffh monomer (left) and the FtsY monomer (right)
are shown, shaded by the change in accessible surface area at
each residue between the monomer and in the heterodimer. The
blue areas define the protein-protein contact. The GTP binding
motifs I to IV are indicated, and the Mg2+ nucleotide ligands
are shown in ball and stick representation. A symmetric
triangular contact region above the active site cavity is termed
the latch. The IBD regions of the two proteins contact one
another below the active site cleft. The packing orientation in
the complex can be visualized by rotating the monomers to
overlay the yellow asterisks. Arrows on the surface of the FtsY
monomer highlight the orientation of the Asp/Lys framework
(black) and the latch interface (pink) presented in the
following panels. (B) The framework formed by Asp229(219) of the
DGQ motif (see table S1) and Lys256(246) of motif IV from both
monomers is shown superimposed to emphasize the symmetry between
Ffh and FtsY in the complex. This symmetric interaction lies
approximately along the diagonal ridge located above the active
site clefts in (A). The lysine hydrogen bonds to both P-loops,
thus bridging the interface. In all figures, residues from FtsY
are labeled in gray italics font and from Ffh in black font. (C)
The symmetric latch interface between the N and G domains,
corresponding to the close loop contacts seen above the adjacent
P-loops in Fig. 1A. The conserved hydrophobic residues of the
ALLEADV motifs of the N domains (top) and the symmetric glycine
pair of the DGQ motifs of the G domains (bottom) are shown along
with the pair of bridging aspartate and glutamine residues.
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