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Figure 4.
Fig. 4. Perturbations of backbone conformation introduced by
the Tyr ladders. (a) Each PSAM mutant was aligned using the most
C-terminal β-hairpin of the SLB, denoted as 0 (residues
187–209). Wild-type (EK)[4] is shown in gray and (YY)[4] in
blue. (YK)[4] overlays almost perfectly with wild type, and its
structure is not depicted. The N- and C-terminal domains along
with the turn regions are omitted for clarity. The backbones of
the β-strands are shown as sticks. (b) Values of the three
parameters, Twist, Bend, and Bend′, describing the
three-dimensional rotations of each β-hairpin in the SLB. Zero
values define a perfectly flat, rectangular β-sheet. Wild-type
(EK)[4] is shown in gray, (YY)[4] in blue, and (YK)[4] in red.
(c) Overpacking of Tyr ladders revealed by hybrid analysis. Each
strand from (YY)[4] was aligned separately with its homologous
strand in wild-type (EK)[4] using all backbone atoms. The
adjusted coordinates of the aromatic side chains were then
grafted onto the wild-type (EK)[4] backbone to form the (YY)[4]
hybrid. Severe steric conflicts (shown as red dots in the
insets) were judged using Probe.^21 Y182 has two side-chain
conformers, and the conflicts were observed for its gauche
conformer but not for its trans conformer.
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