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Figure 4.
Fig. 4. Demonstration of the propagation of small
conformational differences of  -hairpin pairs (i.e.,
four-stranded building blocks) leading to substantial -ribbon
polymorphism. Larger peptide self-assemblies were modeled using
six representative -hairpin pairs.
Different building blocks are shown in different colors (cyan,
5bh molecule C, -hairpin units 4 and 3;
blue, 5bh molecule A, units 3 and2; yellow, 5bh molecule A,
units 5 and 4; green, 5bh molecule C, units 3 and 2; red, 2bh
units 2 and 1), and only the backbone traces of the -strand
regions are shown for clarity. These -hairpin pairs were
superimposed using the first two -strands (labeled with
"1" and "2," respectively). Different relative orientations of
the third and fourth -strands, with respect
to the first and second, are evident. -Ribbon superstructures
shown at Right were constructed in a step-wise manner. Starting
from a four-stranded building block, a copy of the building
block was generated. The third and fourth -strands of the original
block and the first and second -strands of the copy
(which have the identical sequence and nearly identical
conformation; Fig. 2C) were then superimposed. In this way, the
third and fourth -strands of the copy are
now placed as the fifth and sixth -strands of the original
building block, and the relative orientation between adjacent
two-stranded units (i.e., -strands 1–2 and
3–4, and -strands 3–4 and -strand
5–6) is kept identical. These steps were iterated until a
superstructure of sufficient length was generated.
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