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Figure 8.
Figure 8. Conserved residues at the NG interface contribute
to a well-packed interface. Small probe contact dots[8] are
shown at a dot density of 50 dots/Å2. The color of the
dots indicates the types of interactions, with blue dots
indicating wide contacts, greater than 0.25 Å, green
indicating close contacts between 0 Å and 0.25 Å,
yellow indicating small overlaps of less than 0.2 Å, and
purple indicating hydrogen bonds. Hydrogen atoms are included in
the analysis, but are not shown in the Figure. (a) The packing
density around Gly253 and Gly254 (at the center) is especially
tight for glycine residues and thus explains conservation of
these two residues. (b) Leu257 appears to have relatively few
interactions; however, those are with highly conserved residues,
including Leu5, Val43, Leu38, and Leu82. Note the interaction
between Leu5 and Leu257, which involves methyl hydrogen atoms of
the two residues. (c) Interactions with Ser258, which is a
completely conserved residue in the SRP GTPases. Both the
Gly253/Gly254 and Ser258 interactions serve as the "glue" across
the N/G interaction surface.
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